Renal function and plasma arginine vasotocin during an acute salt load in feral chickens

Summary Renal clearance experiments were conducted on feral chickens descended from birds collected from a coral island off the coast of Queensland, Australia. Following a control period when 0.13 M NaCl was used as a vehicle for the renal function markers, a salt load was imposed by infusion of 1 M NaCl. The hypertonic NaCl infusion resulted in increases in glomerular filtration rate (GFR), effective renal blood flow (ERBF), and urine flow rate (V), whereas filtration fraction decreased. Haematocrit was reduced and plasma osmolality, sodium, chloride and potassium concentrations increased. Plasma arginine vasotocin (P_AVT) levels increased from 31.4±2.3 pg·ml^-1 during the control infusion to 56.0±1.7 pg·ml^-1 following a salt load of 12 mmol Nacl·kg^-1 The sensitivity of release of AVT was 0.69±0.11 pg·ml^-1 per mosmol·kg^-1. The concentrations of Na and Cl in urine increased, whereas urine osmolality and potassium concentration decreased. The expansion of the extracellular fluid volume induced by the salt loading would tend to suppress the release of AVT, whereas the osmotic stimulus would provide a stimulus for the release of AVT. In this study, GFR, ERBF and ERPF increased at the same time as P_AVT increased.Abbreviations AVP arginine vasopressin - AVT arginine vasotocin - ERBF effective renal blood flow - ERPF effective renal plasma flow - GFR glomerular filtration rate - P_avt plasma arginine vasotocin concentration - PAH paraaminohippuric acid - SEM standard error of mean - SNGER single nephron glomerular filtration rate - U/P urine to plasma ratio - V urine flow rate     

Effects of caecal ligation and saline acclimation on plasma concentration and organ mass in male and female Pekin ducks,Anas platyrhynchos

Summary The intestinal caeca reabsorb urinary sodium chloride (NaCl) and water (Rice and Skadhauge 1982). Free water may be generated if the reabsorbed NaCl is secreted via salt gland secretion (Schmidt-Nielsen et al. 1958). Therefore ceacal ligation should (a) reduce hingut NaCl and water reabsorption, (b) enhance the increase in plasma osmolality during saline acclimation, and (c) affect drakes more than ducks. Twelve Pekin drakes and 13 Pekin ducks, Anas platyrhynchos, were caecally ligated or sham operated before acclimation to 450 mmol · 1 NaCl. Body mass, hematocrit, plasma osmolality, and inonic concentrations of plasma, cloacal fluid, and salt gland secretion were measured after each increase in drinking water salinity. Osmoregulatory organ masses were determined. Caecal ligation did not effect plasma osmolality or ion concentrations of plasma, cloacal fluid, or salt gland secretion, but reduced salt gland size in ducks. Drakes and ducks drinking fresh water had the same hematocrit, plasma osmolality, and plasma concentrations of Na⁺ and Cl^–. In both sexes exposure to 75 mmol · 1^-1 NaCl significantly decreased plasma [Na⁺] and doubled cloacal fluid [Na⁺]. Exposure to 450 mmol · 1^-1 NaCl decreased body mass and increased hematocrit, plasma [Na⁺], [Cl^–], and plasma osmolality (more in drakes than in ducks); cloacal fluid osmolality nearly doubled compared to freshwater-adapted ducks, due mainly to osmolytes other than Na⁺ and Cl^–. The [Cl^–] in salt gland secretion only slightly exceeded drinking water [Cl^–].Abbreviations AVT antiduretic hormone - CF cloacal fluid - ECFV extraoellular fluid volume - FW freshwater acclimated - Hct hematocrit - MDWE mean daily water flux - [Na ⁺]_cf cloacal fluid sodium concentration - [Na ⁺]_pl plasma sodium concentration - Osm _cf cloacal fluid osmolality - Osm _pl plasma osmolality - SGS salt gland secretion - TBW total body water     

Effects of water restriction during growth and adulthood on renal function of bobwhite quail,Colinus virginianus

Renal function and osmoregulation were studied in bobwhite quail (Colinus virginianus) raised with unrestricted water (chronically unrestricted group) or restricted water (chronically restricted group). There was no difference in urine concentrating ability between adult and juvenile (3.5 or 7.5 week-old) quail. A filtration marker (polyethylene glycol) was infused into adult quail via osmotic minipumps and responses to the following regimens studied: ad libitum water intake, short-term (4-day) water restriction, and acute (1-day) dehydration (withdrawal of all drinking water). Chronically restricted quail had higher urine-to-plasma ratios of polyethylene glycol and lower urine flow rates during short-term restriction. A greater proportion of the reduction in urine flow rate during dehydration was attributable to enhanced tubular reabsorption, rather than reduced rates of filtration, in chronically restricted than in chronically unrestricted birds. Chronically restricted birds also had higher maximum urine-to-plasma ratios of polyethylene glycol (but not higher urine osmolality). These differences occurred in the face of arginine vasotocin concentrations that were not different in the two groups of birds (approximately 15 pg·ml^-1 during hydration, and 45 pg·ml^-1 during water restriction or dehydration). These observations suggest that chronically restricted quail have an enhanced responsiveness of tubular reabsorption to dehydration, a finding consistent with previous observations of tubule hypertrophy and hyperplasia in these birds (Goldstein and Ellis 1991). Despite this, no difference was found in medullary cAMP levels, either basal or arginine vastotocin-or forskolin-stimulated, in the two groups. When given water ad libitum, chronically restricted quail drank copiously (more than two times the drinking rate of chronically unrestricted birds rehydrating from acute dehydration or short-term water restriction), but glomerular filtration rate, hematocrit, and plasma osmolality did not differ in the two groups under this condition; chronically restricted quail excreted the excess water consumed during rehydration in a copious urine accomplished by reduced tubular water reabsorption.Abbreviations ADH antidiuretic hormone - AVT arginine vasotocin - m_b body mass - cAMP cyclic adenosine-monophosphate - DEH birds raised with restricted water intake - dpm decays per minute - ECF extracellular fluid - ECFV extracellular fluid volume - E _PEG total rate of polyethylene glycol excretion - GFR glomerular filtration rate - Hct hematocrit - HYD birds raised with unrestricted water intake - PEG polyethylene glycol - P _osm plasma osmolality - P _PEG plasma concentration of polyethylene glycol - U _PEG urine concentration of polyethylene glycol - (U/P)_PEG urine-to-plasma ratio concentration of polycthylene glycol - V urine flow rate     

Renal function and plasma arginine vasotocin during water deprivation in an Australian parrot,the galah (Cacatua roseicapilla)

Summary Renal function was measured in an Australian parrot, the galah (Cacatua roseicapilla), which is distributed across the most arid regions of the continent. Renal function was assessed by the constant infusion technique in hydrated galahs, and in both hydrated and dehydrated birds by means of osmotic minipumps. The glomerular filtration rate (GFR) of the galah is similar to calculated values for a bird of its size. However, effective renal plasma flow tended to be low and therefore filtration fraction was high. Water deprivation for a period of 5 days caused a decrease in body weight and an increase in plasma osmolality and haematocrit. The GFR declined steadily such that weight-specific GFR on the fifth day of water deprivation was 68% of control values. The water deprivation produced a 2.6-fold elevation of plasma arginine vasotocin (AVT) levels, with an overall sensitivity of release of AVT of 0.16±0.02 pg·ml^-1 per mOsm·kg^-1. The galah possesses renal mechanisms which enable it to conserve significant amounts of water during times of water stress.Abbreviations AVT arginine vasotocin - EDTA ethylene diamine tetra-acetate - GFR glomerular filtration rate - P _AVT plasma arginine vasotocin - PAH para-amino hippuric acid - SNGFR single nephron glomerular filtration rate     

Effects of changes in intravascular oncotic pressure on renal responses to volume loading in the saltwater-acclimated Pekin duck (Anas platyrhynchos)

Summary The relative contributions of the intra-and extravascular compartments of the extracellular fluid (ECF) to the control of osmoregulatory renal functions were examined in saltwater-acclimated Pekin ducks. Having established steady-state diuresis and salt gland secretion by continuous infusion of 1 ml·min^-1 isotonic Krebs-Ringer-Bicarbonate (KRB) solution, 5% dextran-70 was added to the infusate for 30 min thereby confining volume expansion to the intravascular compartment. General volume expansion by isotonic KRB caused a drop in plasma osmolality by 23 mOsm·kg^-1, due to NaCl elimination by the salt glands, and decreases in hematocrit (het) and radioimmunologically measured plasma levels of Arg⁸-vasotocin (AVT) and Val⁵-angiotensin II (ANG II), whereas immunoreactivity associated with atrial natriuretic factor (ir-ANF) was increased. Adding 5% dextran-70 to the infusate left plasma osmolality and electrolytes unchanged but was followed by a further decrease in hct and a 36% increase in the plasma colloidosmotic pressure (COP) facilitating fluid shifts from the extra-to the intravascular compartment of the ECF. Plasma levels of AVT and ANG II remained unchanged, but ir-ANF rose three-fold, its increase being three times as great relative to the decrease in hct, as during general volume expansion by isotonic KRB solution. Arterial and central venous pressure measurements did not indicate changes in cardiovascular function. Hyperoncotic infusion initially induced marked antidiuresis with decreased osmolal excretion, despite a slightly elevated urine osmolality. This effects, however, was trasient and not proportional to the rise in COP, but rather seemed to be related to fluid shifts resulting from hyperoncotic loading. With tracer dilution techniques, reductions in both renal plasma flow and glomerular filtration rate were found to contribute to antidiuresis which was associated with reduced fractional water excretion. Salt gland secretion rate did not increase during hyperoncotic intravascular volume expansion but rather tended to decrease. The results of this study are in line with the idea that contributions of the interstitial fluid compartment (IFC) to volume-dependent control of osmoregulatory functions have to be considered. In the present study on saltwater-acclimated ducks, AVT, ANG II, and ir-ANF could be excluded as mediators of the adjustments in renal water and salt handling following fluid shifts due to hyperoncotic intravascular volume expansion.Abbreviations ANF atrial natriuretic factor - ir-ANF ANF-like immunoreactivity - ANG II angiotensin II - AVT arginine vasotocin - BF breathing frequency - b. w. body weight - COP colloid osmotic pressure - CVP central venous pressure - ECF extracellular fluid - ERPF effective renal plasma flow - FF filtration fraction - GFR glomerular filtration rate - IFC interstitial fluid compartment - i.v. intravenous(ly) - hct hematocrit - HR heart rate - KRB Krebs-Ringer Bicarbonate solution - MABP mean arterial blood pressure - PAH paraaminohippuric acid - SEM standard error of mean     

High dietary sodium chloride and body temperature in the domestic fowl and the Glaucous-winged gull

Arad and Skadhauge (1986) correlated plasma sodium to calcium ratio and body temperature in domestic fowl (Gallus domesticus) during increased dietary sodium chloride intake which increased plasma sodium concentration. During acclimation to high dietary NaCl, body temperature should increase in proportion to the increase in plasma sodium concentration, and body temperature should increase less in gulls than in chickens because salt gland secretion of NaCl by gulls should prevent elevation of plasma sodium concentration. Plasma osmolality, plasma sodium concentration, plasma concentrations of total calcium and ionized calcium, and body temperature and panting threshold were measured in domestic roosters and Glaucous-winged gulls before and after exposure to high NaCl diets. Gull body temperature (40.4±0.2 °C) increased significantly (PM0.05) during salt acclimation. Rooster body temperature (41.0±0.2 °C) did not increase significantly. Plasma sodium concentration increased in gulls (5.4±0.5%, P<0.01) and was correlated with body temperature (r=0.497, P<0.05); the 3.8±1.0% increase in plasma sodium concentration in roosters (P<0.01) was not, suggesting that change in body temperature might be a response to the magnitude of increase in plasma sodium concentration. Plasma ionized calcium concentration increased by 12.9±4.6% (P<0.01) in gulls and by 5.3±1.0% (P<0.01) in roosters. Plasma sodium concentration was correlated with calcium ion concentration in both gulls (r=0.635, P<0.05) and roosters (r=0.664, P<0.05). In neither species were ratios of sodium to total calcium plasma concentration or sodium to ionized calcium concentration altered or related to body temperature. Panting threshold increased significantly in roosters following salt acclimation, but not in gulls due to high variability in response. The increase in gull plasma sodium concentration was small compared to previously reported (Saxena 1976; Denbow and Edens 1980, 1981; Maki et al. 1988) increases in hypothalamic and intraventricular sodium concentration following infusion of Na⁺, yet the effect on body temperature was similar in both types of studies. This suggests that sodium may have peripheral effects that augment the central effects imposed by altered hypothalamic interstitial sodium and calcium concentration.Abbreviations [Ca]_p1 total calcium concentration in plasma - [Ca²⁺] ionized calcium concentration in plasma - [Cl]_p1 chloride concentration in plasma - f respiratory frequency - Hct hematocrit - [K]_p1 potassium concentration in plasma - [Na]_p1 sodium concentration in plasma - osm_p1 plasma osmolality - PT panting threshold - T _a ambient temperature - T _b body temperature - V _t tidal volume     

The effect of infusion of hypertonic saline on glomerular filtration rate and arginine vasotocin, prolactin and aldosterone in the domestic chicken

Domestic fowl were infused for 60 min with isotonic saline followed by 90 min with hypertonic saline. Plasma electrolyte concentrations, osmolality and haematocrit were measured. Urine electrolyte excretion rates, osmolar output and urine flow rates were also monitored. From these results fractional excretions of electrolytes were calculated. The renal function markers inulin and ρ-amino hippuric acid were infused to enable the measurement of glomerular filtration rate and plasma clearance of ρ-amino hippuric acid, respectively. Plasma samples were also taken to assay for the hormones prolactin, aldosterone and arginine vasotocin. Plasma electrolytes and osmolality, fractional excretion of electrolytes and osmolar output all increased, while haematocrit decreased, throughout the experiment. However, no significant change was found in urine flow rate and little change was seen in glomerular filtration rate. The clearance of ρ-amino hippuric acid, which provides an indication of renal plasma flow, increased during hypertonic saline infusion. Plasma concentrations of aldosterone and prolactin decreased during the experiment and plasma concentrations of arginine vasotocin increased. Infusion of hypertonic saline had no consistent effect on glomerular filtration rate, which may be due to conflicting influences of expansion of the extracellular fluid volume and increased plasma osmolality. Accepted: 19 January 1998     

Osmoregulation in nestling California gulls at Mono Lake,California

• 1.1. Hematocrit (Hct), plasma sodium ([Na]_pl), chloride ([Cl]_pl) and osmotic concentration (Osm_pl); volume and concentration of 1.0MNaCl induced salt gland secretion (SGS); and weights of osmoregulatory organs: kidneys, adrenal glands, and salt glands and nonosmoregulatory organs (liver and heart) were determined in nestling California gulls, Larus californiens (CG), on Krakatoa Islet, Mono Lake, California.
• 2.2. The mean Hct was 40.0% + 1.0%, the mean [Na]_pl and [Cl]_pl were 153.9 ± 0.9 and 110.1 ± 0.5 mM (n = 22); and the mean Osm_pl was 323.6 ± 1.3 mOsm/kg (n = 18).
• 3.3. In CG nestlings with a mean age of 10 days (n = 7), the mean SGS [Na] was 719 ± 19 mM and the birds secreted 81 ± 18% of the injected fluid containing 59 ± 13% of the injected Na. By the mean age of 23 days (n = 7), mean SGS [Na] was slightly higher (790 ± 30 mM than in younger birds (P < 0.05), but the percentage of secreted fluid (54 ± 10%) and Na (42 ± 6%) tended to be less.
• 4.4. In 18 CG nestlings mean organ weights (% body weight) were: kidneys 1.52 ±0.06%; salt glands, 0.13 ±0.01%, and adrenal glands 0.07 ±0.01%.
• 5.5. Nestling CG had significantly greater Hct (P < 0.001), [Na]_pl and [ci]_pl (P < 0.001), Osm_pl, (P < 0.005), and adrenal gland weight (P < 0.01), compared to nestling glaucous-winged Gulls (GWG), L. glaucescens (Hughes, 1984), which nest under cooler, moister conditions. CG kidney weight was smaller (P < 0.001); salt gland weight and salt excretion were the same as GWG.

     

Salt gland function in the common eider duck (Somateria mollissima)

The function of the supra-orbital salt gland was studied in the common eider duck (Somateria mollissima). The maximum salt-secreting capacity was determined in (1) wild ducks which had been living in a marine environment, (2) ducks reared in captivity on fresh water, and (3) ducks from group 2 adapted to salt water. The maximum secreting capacity was found by infusing a solution of NaCl (1000 mosmol·kg^-1) at increasing rates, from 0.691 to 1.671 mosmol·min^-1. Freshwater-adapted ducks secreted at a maximum rate of 0.785 mosmol·min^-1 (1500 mosmol·kg^-1). Adapted to salt water they increased their capacity, and the best duck secreted at a rate of 1215 mosmol·min^-1 (1600 mosmol·kg^-1). The best wild duck secreted at a rate of 1516 mosmol·min^-1. Ducks in group 3 were used to examine the response to a hyperosmotic or an isoosmotic infusion. The amount of salt (NaCl) given per unit time was the same. Given a hyperosmotic solution their salt glands secreted at a high rate: 30 min after the infusion had stopped the ducks had excreted 94% of the sodium infused, 92.9% via the salt gland. Given an isoosmotic solution they secreted at a rate about half the infusion rate: 30 min after cessation of infusion they had excreted 73% of the sodium, 42.9% via the salt gland and the rest by the kidneys.Abbreviations A II angiotensin II - AV I arginine vasotocin - ED freshwater-adapted ducks - FW fresh water - SD saltwater-adapted ducks - SW sea water - WD wild ducks     

Arterial hypotension in ducks adapted to high salt intake

Summary A homogeneous group of 8-week-old Pekin ducks was divided into two groups: saltwater (SW) ducks received salt water of gradually increasing salinity (200–600 mOsm·kg^-1) from the 8th to 20th week of age; freshwater (FW) ducks were maintained on fresh water but otherwise treated identically. During the course of salt-adaptation SW ducks increased plasma osmolality, Na⁺ and Cl^- levels, and concentrations of the osmoregulatory peptide hormones arginine vasotocin and angiotensin II. The apparent volume of inulin distribution decreased in SW ducks, but blood volume was not reduced. SW ducks also developed arterial hypotension, bradycardia, and reduced cardiac output in the course of salt adaptation. This depressed cardiovascular performance was associated with enhanced vagal restraint of cardiac function and reduced plasma concentrations of norepinephrine. Salt water adaptation did not alter the degrees to which mean arterial pressure and heart rate changed in response to intravenous bolus injections of catecholamines. The same applied to the osmoregulatory peptides which were, however, effective only at supraphysiological concentrations. The Pekin duck, as a bird predisposed for adaptation to high salt loads, presumably adapts to chronic hypertonic saline intake by resetting the central autonomic control of blood pressure to a lower level.Abbreviations FW ducks fresh water ducks - SW ducks salt water ducks - ANGI angiotensin II - AVT arginine vasotocin - MAP mean arterial pressure - HR heart rate - IV intravenous - CO cardiac output - SV stroke volume - TPR total peripheral resistance - ISp virtual inulin space - ECFV extracellular fluid volume     

Osmolality and volume factors in salt gland control of pekin ducks after adaptation to chronic salt loading

Summary Pekin ducks were adapted to permanent osmotic stress by rearing them on a NaCl solution of increasing concentration up to 2% as drinking water. Their salt and water balance was compared with that of non-adapted ducks maintained on tap water. Amounts and osmolalities of salt gland secretion and cloacal discharges, plasma osmolality and electrolytes were measured during stepwise osmotic loading by intravenous infusion of NaCl solution of about 740 mosm·kg^–1, at rates of 0.25, 0.45 and 0.65 ml·min^–1. Before loading, the plasma osmolality of the adapted ducks was about 22 mosm·kg^–1 higher than in non-adapted animals. The initial step of loading induced salt gland secretion in the adapted ducks after an average rise of plasma osmolality of 3.6 mosm·kg^–1 and in the non-adapted animals after a rise of 7.8 mosm·kg^–1. The method of osmotic loading enabled both groups of animals to balance their water input and output. However, only the adapted ducks were able to balance NaCl input and output, predominantly by salt gland secretion, thus maintaining a stable plasma osmolality. The nonadapted ducks retained 42% of the salt load which resulted in a rise of plasma osmolality of 49 mosm·kg^–1, more salt being excreted by the kidneys than by the salt glands.In the salt-adapted ducks, salt gland activity, plasma osmolality and Na⁺ concentration did not correlate during balanced states of salt input and output. The involvement of tonicity receptors in salt gland control was confirmed by the stimulating effects of various hypertonic solutions. On the other hand, continuous loading by a constant infusion of NaCl solution of 1,300 mosm·kg^–1 induced a steady salt gland secretion at a rising plasma osmolality and thus suggested that a volume factor is involved in salt gland control. Inhibition of salt gland activity by withdrawing blood and activation by blood infusion confirmed this assumption. While a direct cause and effect relationship between volume changes and salt gland secretion cannot be demonstrated, the results indicate that volume changes in one or more extracellular compartments do affect salt gland secretion.Supported by Deutsche Forschungsgemeinschaft (Si 320/2)     

Control of renal function in larvalAmbystoma tigrinum

Summary Renal clearance methods were used to examine several factors which may be involved in control of urine flow in larvalAmbystoma tigrinum. Arginine vasotocin (10 ng/g) reduced both urine flow and GFR (–30%); this was reversed with mesotocin (5 ng/g). Adaptation to isosmotic media reduced GFR from 0.156 ml/10 g·h to 0.057. Neither hypophysectomy nor treatment with mesotocin altered this response. The adrenergic blocking agents propranolol and phentolamine did not reverse the antidiuresis in isosmotic medium-adapted larvac. Ten percent volume expansion with 50% and 100% Ringer's solution increased GFR in isosmotic medium-adapted animals. Hypophysectomy prevented this increase in GFR. Ten percent volume expansion with 200% Ringer's solution decreased GFR in tapwater adapted larvae; however, 20% volume expansion with 200% Ringer's increased GFR. Both volume and concentration of extracellular fluid appear to be important in control of GFR. Both arginine vasotocin and mesotocin may be involved in these responses, however other factors must also play a role.Abbreviations AVT arginine vasotocin - ECF extracellular fluid - GFR glomerular filtration rate - MT mesotocin     

Renal,respiratory and ionic regulation in Atlantic salmon (Salmo salar L.) kelts following transfer from fresh water to seawater

Summary Atlantic salmon may return to the sea after spawning in fresh water. These fish, known as kelts, reportedly show a limited ability to hypoosmoregulate. However, this study shows that fresh-water-adapted kelts exposed to seawater demonstrate rapid adaptation (within 48 h) in osmoregulatory parameters to values characteristic of seawater-adapted salmonids. The urine flow rate falls from 1.2 to 0.2 ml·kg^-1·h^-1 within 24 h. Over the same period, urine osmolality increases from 48 mosmol·kg^-1 to become isosmotic with the plasma, and Mg²⁺ secretion by the kidney tubules elevates the urine concentration from 0.5 to 100 mmol·l^-1. As is characteristic for marine teleosts, kelts drink seawater and process the ingested water in the gut to replace body water lost by osmosis to the hyperosmotic medium. Seawater exposure causes a marked hypoxia, arterial oxygen tension falling by 43% within minutes and persisting for at least 4 days at this low level. This is associated with large changes in blood pH and acid-base balance. The physiological mechanisms involved in adaptation to a hyperosmotic external medium are discussed, and the osmoregulatory capacity of kelts is compared with that of salmon at other stages of the life cycle.Abbreviations FW fresh water - GFR glomerular filtration rate - Hb haemoglobin - Hct haematocrit - MCHC mean cell haemoglobin concentration - pH_a pH in arterial blood - P _aO₂ partial pressure of oxygen in arterial blood - SEM standard error of mean - SW seawater - UFR urine flow rate     

Renal function and organic anion and cation transport during dehydration and/or food restriction in chickens

The effect of dehydration in the presence or absence of continued food intake on renal function was evaluated in chickens. In addition, renal transport of organic anions and cations under these conditions was assessed in vitro by uptake of ¹⁴C-para-aminohippuric acid and ¹⁴C-tetraethylammonium bromide by renal slices. Water restriction with continued food intake resulted in increases in serum osmolality and serum concentrations of sodium, uric acid, calcium and total protein. If food was restricted in addition to water, only serum osmolality and sodium concentration were significantly increased after 48 hours. Dehydration with continued access to food resulted in marked decreases in extracellular fluid volume, glomerular filtration rate and effective renal plasma flow. If food was restricted during dehydration, the decrease in effective renal plasma flow was attenuated despite reductions in glomerular filtration rate and extracellular fluid comparable to that seen in dehydrated birds allowed free access to food. Transport of organic anions was significantly increased after 24 and 48 hours of water restriction, regardless of whether food was withheld. Enhanced transport of organic anions in the presence of decreased glomerular filtration rate and effective renal plasma flow during dehydration may promote precipitation of urates and nephrosis in chickens.Abbreviations cpm counts per minute - dpm disintegrations per minute - ECF extracellular fluid - ERPF effective renal plasma flow - GFR glomerular filtration rate - PAH para-aminohippuric acid - SEM standard error of the mean - TEA tetraethylammonium bromide     

Fractional reabsorption of calcium,magnesium and phosphate in the kidneys of freshwater North American eels (Anguilla rostrata LeSueur) following removal of the corpuscles of Stannius

Renal function was observed in freshwater North American eels (Anguilla rostrata LeSueur) 2 weeks after the removal of the corpuscles of Stannius. There was a positive linear correlation between glomerular filtration rates and urine flow rates in both sham-operated and stanniectomized eels but there was no difference in slope or elevation between the two groups nor did urine flow rates ever exceed glomerular filtration rates. Osmolar clearance and free-water clearance were unchanged following stanniectomy. Plasma Ca²⁺ and K⁺ concentrations increased and plasma Mg²⁺, phosphate, Na⁺ and Cl^- concentrations decreased following stanniectomy. Plasma ultrafilterable Ca increased and ultrafilterable Mg decreased after stanniectomy but neither changed relative to its total plasma concentration. Stanniectomy was followed by a decreased renal tubular reabsorption of Mg²⁺ relative to the amount filtered (C _Mg/C _In); the same applies to C _Na/C _In. Even though the filtered load of Ca increased in conjuction with the predictable hypercalcemia, there was no change in the fraction of filtered Ca reabsorbed. Net tubular secretion of phosphate was observed in both sham-operated and stanniectomized cels together with a slight increase in C _phos/C _In following stanniectomy. Some or all of these changes in plasma electrolytes and/or the modified renal transport of Na⁺, Mg²⁺ and possibly phosphate may be caused by the changes in cardiovascular function that were recently shown to follow stanniectomy.Abbreviations CSX Stanniectomized/stanniectomy - ER endoplasmatic reticulum - FW fresh water - GFR glomerular filtration rate - Pi inorganic phosphate - RAS renin-angiotensin system - SHM sham-operated - SW sea water - UFR urine flow rate - U/P ratio urine/plasma ratio     

Regulation of salt gland, gut and kidney interactions

Marine birds can drink seawater because their cephalic 'salt' glands secrete a sodium chloride (NaCl) solution more concentrated than seawater. Salt gland secretion generates osmotically free water that sustains their other physiological processes. Acclimation to saline induces interstitial water and Na move into cells. When the bird drinks seawater, Na enters the plasma from the gut and plasma osmolality (Osm(pl)) increases. This induces water to move out cells expanding the extracellular fluid volume (ECFV). Both increases in Osm(pl) and ECFV stimulate salt gland secretion. The augmented intracellular fluid content should allow more rapid expansion of ECFV in response to elevated Osm(pl) and facilitate activation of salt gland secretion. To fully utilize the potential of the salt glands, intestinally absorbed NaCl must be reabsorbed by the kidneys. Thus, Na uptake at gut and renal levels may constrain extrarenal NaCl secretion. High NaCl intake elevates plasma aldosterone concentration of Pekin ducks and aldosterone stimulates intestinal and renal water and sodium uptake. High NaCl intake induces lengthening of the small intestine of adult Mallards, especially males. High NaCl intake has little effect on glomerular filtration rate or tubular sodium Na uptake of birds with competent salt glands. Relative to body mass, kidney mass and glomerular filtration rate (GFR) are greater in birds with salt glands than in birds that do not have them. Birds with salt glands do not change GFR, when they drink saline. Thus, their renal filtrate contains excess Na that is, in some species, almost completely renally reabsorbed and excreted in a more concentrated salt gland secretion. Na reabsorption by kidneys of other species, like mallards is less complete and their salt glands make less concentrated secretion. Such species may reflux urine into the hindgut, where additional Na may also be reabsorbed for extrarenal secretion. During exposure to saline, marine birds maintain elevated aldosterone levels despite high Na intake. Marine birds are excellent examples of physiological plasticity.     

Capacitance,short-circuit current and osmotic water flow across different regions of the isolated toad skin

Summary The amphibian antidiuretic hormone, arginine vasotocin, stimulated osmotic water flow across isolated skin from the pelvic but not the pectoral skin of the toad, Bufo woodhouseii. Changes in the apical membrane capacitance were not observed for either region of the skin following treatment with arginine vasotocin when there was an osmotic gradient across the tissue. In the absence of an osmotic pressure gradient, the apical membrane capacitance of the pelvic skin increased from 2.8±0.5 to 3.3±0.6 F · cm^-2 after treatment with 5 · 10^-8 M arginine vasotocin. Under these conditions, apical membrane capacitance of the pectoral skin was 1.8±0.1 F · cm^-2 and did not change significantly after arginine vasotocin treatment. The amiloride-sensitive short-circuit current across the pelvic skin was stimulated by arginine vasotocin as was the density of channels in the apical membrane as determined by fluctuation analysis. Values for channel density in the pelvic skin also correlated with apical membrane capacitance and increased from 90 to 273 channels per m² of estimated membrane area following arginine vasotocin treatment. In the pectoral skin the stimulation of short-circuit current following arginine vasotocin treatment was small and an increase in channel density could not be demonstrated. The current through single Na⁺ channels in both regions of the skin did not different either before or after arginine vasotocin treatment.Abbreviations A amiloride - ADH antidiuretic hormone - AVT arginine vasotocin - C capacitance - C _a capacitance of apical membrane - f _c corner frequency - i single-channel current - osmotic water flow - IMP intramembrane particles - I _sc short-circuit current - amiloride-sensitive short-circuit current - M channel density - P _o probability of a channel being open - R channel receptor - R _a apical resistance - R _p paracellular resistance     

The effect of carbonic anhydrase inhibitors on secretion by the parotid and mandibular glands of red kangaroos Macropus rufus

Summary The effects of carbonic anhydrase inhibitors on secretion by macropodine parotid and mandibular glands were investigated using anaesthetized red kangaroos. In the parotid gland, acetazolamide (500 mol·l^-1) reduced a stable acetylcholine-evoked, half-maximal flow rate of 2.02±0.034 to 0.27±0.023 ml·min^-1 (87% reduction). Concurrently, salivary bicarbonate concentration and secretion fell (129.4±1.46 to 80.9±1.63 mmol·l^-1 and 264.8±7.96 to 22.3±2.30 mol·min^-1, respectively), phosphate and chloride concentrations rose (14.0±0.79 to 27.6±0.85 mmol·l^-1 and 5.6±0.25 to 27.5±1.32 mmol·l^-1, respectively), sodium concentration and osmolality were unaltered, and potassium concentration fell (8.8±0.33 to 6.4±0.29 mmol·l^-1). High-rate cholinergic stimulation during acetazolamide blockade was unable to increase salivary flow beyond 11±0.9% of that for equivalent unblocked control stimulation. However, superimposition of isoprenaline infusion on the acetylcholine stimulation caused a three-fold increase in the blocked flow rate. These treatments were accompanied by small increases in salivary phosphate and chloride concentrations but not bicarbonate concentration. Methazolamide infusion caused similar changes in parotid secretion. In the mandibular gland, acetazolamide infusion had no effect on salivary flow rate during either low- or high-level acetylcholine stimulation. Acetazolamide caused no alterrations in salivary electrolyte secretion at low flow rates, but curtailed the rise in bicarbonate concentration associated with high-level acetylcholine stimulation. Acetazolamide administration did not affect the increase in salivary flow rate associated with isoprenaline infusion, but did block the concomitant increase in bicarbonate concentration and secretion substantially. It was concluded that neither cholinergic nor adrenergic stimulation of mandibular fluid secretion depends on secretion of bicarbonate derived from catalysed hydration of CO₂, but a substantial proportion of the increase in bicarbonate secretion during isoprenaline administration, which is probably ductal in origin, is so dependent. In contrast to other salivary glands, including the ovine parotid, fluid secretion by the kangaroo parotid gland during cholinergic stimulation is largely dependent (about 90%) on secretion of bicarbonate derived from hydration of CO₂ catalysed by glandular carbonic anhydrase. Fluid secretion during adrenergic stimulation is not bicarbonate dependent.Abbreviations b.w. body weight - PAH p-aminohippurate - PCO₂ partial pressure carbon dioxide - PCO₂ partial pressure of oxygen     

Vasotocin acts as a dipsogen in ducks at concentrations stimulating subfornical organ neurons in vitro

The effects of systemic infusions of the avian antidiuretic hormone arginine vasotocin on water intake of domestic ducks were investigated under steady conditions of water balance in which angiotensin II was effective as a dipsogen. The study proceeded from the consistent stimulatory effect of arginine vasotocin on angiotensin II-responsive neurons found in the subfornical organ of ducks, suggesting brain-intrinsic vasotocinergic control of these neurons which are also accessible to circulating agents because of the lacking blood-brain barrier. Levels of circulating arginine vasotocin of about 2700 pg·ml^-1 which were close to the threshold for activation of subfornical organ neurons in vitro, induced weak but significant drinking responses. Even at this high arginine vasotocin level circulatory effects were absent, thereby excluding their interference with water intake. Arginine vasotocin plasma levels of about 60 pg·ml^-1 significantly attenuated the dipsogenic action of angiotensin. While drinking in response to high pharmacological levels of arginine vasotocin is assumed to mimic a stimulatory innervation of angiotensin-responsive subfornical organ neurons by brain-intrinsic vasotocinergic axons, attenuation of angiotensin-induced drinking by high physiological arginine vasotocin levels cannot be explained by its action on central neurons, but may be secondary to body fluid retention caused by the antidiuretic action of arginine vasotocin.Abbreviations ADH antidiuretic hormone - ANGII angiotensin II - AVP arginine vasopressin - AVT arginine vasotocin - BBB blood-brain barrier - HR heart rate - ICV intracerebroventricular - IV intravenous - MAP mean arterial pressure - SFO subfornical organ     

Osmotic,sodium, carbon dioxide and acid-base state of the Port Jackson shark,<Emphasis Type="Italic"> Heterodontus portusjacksoni</Emphasis>, in response to lowered salinity

In marine elasmobranch fish the consequences for CO₂ and acid–base state of moving into low salinity water are not well described. Sub-adult Port Jackson sharks, Heterodontus portusjacksoni, occasionally enter brackish water and survive in 50% seawater (SW). The unidirectional Na efflux and content, plasma volume, glomerular filtration rate (GFR), body mass, as well as CO₂ and acid-base state in H. portusjacksoni were investigated following transfer from 100% SW to 75% SW and then to 50% SW. A rapid water influx resulted in a doubling of the plasma volume within 24 h in sharks in 75% SW and an 11% increase in body weight. Osmotic water influx was only partially offset by a doubling of the GFR. There was a ~40% decrease in plasma [Na] through a transiently elevated Na clearance and haemodilution. The result was a decrease in the inward gradient for Na⁺ together with reductions of nearly 50% in CO₂ and buffer capacity. The sharks remained hypo-natric to 50% SW by partially conforming to the decrease in external osmotic pressure and avoided the need for active Na⁺ uptake. The gradient for Na⁺ efflux would by extrapolation approach zero at ~27% SW which may of itself prove a lethal internal dilution. In sharks transferred to 75% SW, a small transient hypercapnia and a later temporary metabolic alkalosis were all largely explained through anaemia promoting loss of CO₂ and buffer capacity. In sharks transferred to 50% SW the metabolic alkalosis persisted until the end of the 1-week trial. Within the erythrocytes, increased pH was consequent on the large decrease in haemoglobin content exhibited by the sharks, which caused a large reduction in intracellular buffer. In water as dilute as 50% SW there was no evidence of specific effects on the mechanisms of management of CO₂ or H⁺ excretion but rather significant and indirect effects of the severe haemodilution.Abbreviations a–v arterial–venous - CA carbonic anhydrase - C _a CO ₂ content of CO₂ in arterial blood - CCO ₂ CO₂ content - ⁵¹ Cr-EDTA ⁵¹chromium-ethylenediaminetetraactic acid - C _v CO ₂ content of CO₂ in venous blood - FW freshwater - GFR glomerular filtration rate - Hct haematocrit - J _out Na flux rate - MCHC mean cell haemoglobin concentration - OP osmotic pressure - P _a CO ₂ partial pressure of CO₂in arterial blood - PCO ₂ partial pressure of CO₂ - pH _a arterial blood pH - pH _er intra-erythrocyte fluid - pH _pl whole blood pH - pH _v venous blood pH - P _v CO ₂ partial pressure of CO₂in venous blood - SID strong ion difference - SW seawater - TMAO trimethylamine-N-oxide - UFR urinary flow rate Communicated by G. Heldmaier