Renal function at steady state in a toad (Bufo viridis) acclimated in hyperosmotic NaCl and urea solutions

Kidney function of the euryhaline toad Bufo viridis was studied in animals acclimated to tap water and solutions of NaCl (230 and 500 mosmol · kg^-1 H₂O) and urea (500 mmol · l^-1) in steady-state conditions. An ureter was eatheterized for continuous urine collection and blood was sampled from an iliac artery. A single injection of ³H-inulin served for estimation of glomerular filtration rate: this was in the range of 15–27 ml · kg^-1 · h^-1 and did not differ significantly in any of the acclimation conditions. Urine flow, on the other hand, varied considerably and was highest in tap water (18.2±3.2 ml · kg^-1 · h^-1; urine/plasma inulin ratio=0.88), lower in 230 mosmol · kg^-1 H₂O NaCl solution (13.5±3.9 ml · kg^-1 · h^-1; u/p inulin ratio=1.73) and lowest in 500 mosmol · kg^-1 H₂O NaCl or urea acclimation solutions (5–7 ml · kg^-1 · h^-1; u/p inulin=3.7–4.2). Clearance of free water was high in the tap water group, lower in 230 mosmol · kg^-1 H₂O NaCl solution, and much lower in the hyperosmotic acclimation conditions. Clearances of both Na⁺ and Cl^- were similar under our experimental conditions, but changed independently in accordance to the composition of the acclimation solution. Potassium clearance was similar in all acclimation conditions, and a constant plasma K⁺ concentration was maintained. Urea clearance was high in tap water and 500 mmol · l^-1 urea acclimation groups and low in the NaCl acclimations. The experiments show that the glomerular filtration rate remains more or less unchanged in all acclimation conditions, and suggest that the different rates of urine flow at steady state must be due mostly to tubular processes. The final composition of the urine is the result of specific and highly selective tubular processes.Abbreviations %T fractional reabsorbance - AVT argine vasotocin - C _{free water} free water clearance - C _osmol osmolyte clearance - GFR glomerular filtration rate - MS-222 methanetricaine sulphonate - U/P urine to plasma inulin ratio - V volume     

The physiological responses of freshwater rainbow trout,Oncorhynchus mykiss,during acutely lethal copper exposure

Acutely lethal (24 h) exposure of adult rainbow trout (Oncorhynchus mykiss) to 4.9 mol copper·l^-1 in fresh water (pH 7.9, [Ca²⁺]0.8 mEq·l^-1) caused a rapid decline of plasma Na⁺ and Cl^- and arterial O₂ tension, and initially a pronounced tachycardia. The internal hypoxia probably resulted from histopathologies observed in the gills of fish exposed to copper, such as cell swelling, thickening and curling of the lamellae, and haematomas. Copper cannot therefore be considered purely as an ionoregulatory toxicant during acutely lethal conditions. Mortality during exposure to copper could not simply be explained by the plasma ionic dilution, nor by the internal hypoxia, since arterial O₂ content remained relatively unchanged. Secondary to the ionoregulatory and respiratory disturbances were a number of deleterious physiological responses which included a massive haemoconcentration (haematocrit values as high as 60%) and a doubling of the mean arterial blood pressure. The time-course of these changes suggest that cardiac failure was the final cause of death. In this respect copper exposure resembles low pH exposure in freshwater trout (Milligan and Wood 1982). Copper and H⁺ appear to be similar in both the primary site of their toxic action (the gills) and the secondary physiological consequences which result from acutely lethal exposures. Furthermore, the acute toxicity syndrome observed may be common to many metals which cause ionoregulatory and/or respiratory problems in freshwater fish.Abbreviations C _aO₂ arterial oxygen content - FR water flow rate - Hb haemoglobin - Hct haematocrit - H _m ⁺ net metabolic acid load - IU international unit - MABP mean arterial blood pressure - MCHC mean corpuscular haemoglobin content - MO₂ rate of oxygen consumption - P _aCO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen partial pressure - T _amm total ammonia (=NH₃+NH ₄ ⁺ ) - TCO₂ total carbon dioxide - TOC total organic carbon - %Hb–O₂ percentage of haemoglobin saturated with oxygen     

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     

Oxygen transport and cardiovascular responses in skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) exposed to acute hypoxia

Summary Responses to acute hypoxia were measured in skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) (1–3 kg body weight). Fish were prevented from making swimming movements by a spinal injection of lidocaine and were placed in front of a seawater delivery pipe to provide ram ventilation of the gills. Fish could set their own ventilation volumes by adjusting mouth gape. Heart rate, dorsal and ventral aortic blood pressures, and cardiac output were continuously monitored during normoxia (inhalant water (PO ₂>150 mmHg) and three levels of hypoxia (inhalant water PO ₂130, 90, and 50 mmHg). Water and blood samples were taken for oxygen measurements in fluids afferent and efferent to the gills. From these data, various measures of the effectiveness of oxygen transfer, and branchial and systemic vascular resistance were calculated. Despite high ventilation volumes (4–71·min^-1·kg^-1), tunas extract approximately 50% of the oxygen from the inhalant water, in part because high cardiac outputs (115–132 ml·min^-1·kg^-1) result in ventilation/perfusion conductance ratios (0.75–1.1) close to the theoretically ideal value of 1.0. Therefore, tunas have oxygen transfer factors (ml O₂·min^-1·mmHg^-1·kg^-1) that are 10–50 times greater than those of other fishes. The efficiency of oxygen transfer from water in tunas (65%) matches that measured in teleosts with ventilation volumes and order of magnitude lower. The high oxygen transfer factors of tunas are made possible, in part, by a large gill surface area; however, this appears to carry a considerable osmoregulatory cost as the metabolic rate of gills may account for up 70% of the total metabolism in spinally blocked (i.e., non-swimming) fish. During hypoxia, skipjack and yellowfin tunas show a decrease in heart rate and increase in ventilation volume, as do other teleosts. However, in tunas hypoxic bradycardia is not accompanied by equivalent increases, in stroke volume, and cardiac output falls as HR decreases. In both tuna species, oxygen consumption eventually must be maintained by drawing on substantial venous oxygen reserves. This occurs at a higher inhalant water PO₂ (between 130 and 90 mmHg) in skipjack tuna than in yellowfin tuna (between 90 and 50 mmHg). The need to draw on venous oxygen reserves would make it difficult to meet the oxygen demand of increasing swimming speed, which is a common response to hypoxia in both species. Because yellowfin tuna can maintain oxygen consumption at a seawater oxygen tension of 90 mmHg without drawing on venous oxygen reserves, they could probably survive for extended periods at this level of hypoxia.Abbreviations BP_da, BP_va dorsal, ventral aortic blood pressure - C _aO₂, C _vO₂ oxygen content of arterial, venous blood - DO₂ diffusion capacity - E_b, E_w effectiveness of O₂ uptake by blood, and from water, respectively - Hct hematocrit - HR heart rate - PCO₂ carbon dioxide tension - P _aCO₂, P _vCO₂ carbon dioxide tension of arterial and venous blood, respectively - PO₂ oxygen tension - P _aO₂, P _vO₂, P _iO₂, P _cO₂ oxygen tension of arterial blood, venous blood, and inspired and expired water, respectively - pHa, pHv pH of arterial and venous blood, respectively - P_w—b effective water to blood oxygen partial pressure difference - Pg partial pressure (tension) gradient - cardiac output - R vascular resistance - SV stroke volume - SEM standard error of mean - TO₂ transfer factor - U utilization - _g ventilation volume - O₂ oxygen consumption     

Differential responses to copper in rainbow trout (Oncorhynchus mykiss) acclimated to sea water and brackish water

Rainbow trout, Oncorhynchus mykiss, acclimated to 33% sea water (12 mg·ml^-1 salinity) experienced significant (10 meq·1^-1) increases in plasma [Na⁺] and [Cl^-] within 5 h of exposure to 6.3 mol copper·1^-1 indicating severe impairment of branchial ionoregulatory capacity. All plasma ion levels subsequently stabilised once the transbranchial [Na⁺] gradient was reduced to zero. The similar ionic strength of the external medium and their body fluids appeared to protect trout maintained in 33% sea water from further ionoregulatory stress and any secondary physiological disturbances during exposure to copper. Despite three- and fourfold greater transbranchial [Na⁺] and [Cl^-] gradients, trout acclimated to full-strength sea water (35 mg·ml^-1 salinity) suffered no major changes in plasma Na⁺, Cl^-, K⁺, or Ca²⁺, blood gases or haematology during 24 h exposure to 6.3 mol copper·1^-1. This reduction in toxicity in full strength sea water cannot be explained by differences in copper speciation. We suggest that during acute exposure to waterborne copper, active NaCl extrusion is unaffected due to the basolateral location of the gill Na⁺/K⁺-ATPase, but that ionoregulatory disturbances can occur due to gill permeability changes secondary to the displacement of surface-bound Ca²⁺. However, in full strength sea water the three-fold higher ambient [Ca²⁺] and [Mg²⁺] appear to be sufficient to prevent any detrimental permeability changes in the presence of 6.3 mol copper·1^-1. Plasma [NH ₊ ⁴ ] and [HCO _- ³ ] were both significantly elevated during exposure to copper, indicating that some aspects of gill ion transport (specifically the apical Na⁺/NH ₊ ⁴ and Cl^-/HCO _- ³ exchanges involved in acid/base regulation and nitrogenous waste excretion) are vulnerable to inhibition in the presence of waterborne copper.Abbreviations C _aO₂ arterial oxygen content - Hb haemoglobin - Hct haematocrit - MABP mean arterial blood pressure - MCHC mean cell haemoglobin content - MO₂ rate of oxygen consumption - P _a CO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen partial pressure - S salinity - SW sea water - T _Amm total ammonia (=NH₃+NH ₊ ⁴ ) - T _{CO 2} total carbon dioxide - TEP transepithelial potential - TOC total organic carbon - %Hb-O₂ percentage of haemoglobin saturated with oxygen     

Effect of water restriction on energy and water balance and osmoregulation of the fruit bat Rousettus aegyptiacus

The energy budget, water balance and osmoregulation of the fruit bat, Rousettus aegyptiacus, were studied during normal hydration and during water restriction (oven-dried apple diet). The water input and output were balanced during both normal hydration and water restriction. The kidney of the fruit bat is well adapted to handle the water load from its fruit diet by excreting large volumes (14% of the body mass per day) of dilute urine (113±25 mosmol·kg H₂P^-1) as well as reducing urine volume (-95%) and increasing urine osmotic concentration (555±280 mosmol·kg H₂O^-1) during water restriction. The haematocrit, plasma haemoglobin and total protein concentrations did not increase during water restriction and heat exposure, suggesting the conservation of plasma volume. Gross energy intake was not alfected by water restriction. However, digested energy intake and digestibility were significantly reduced. The effective regulation of energy and water budgets during water restriction suggests that the fruit bat can cope with seasonal climatic changes and with variable fruit supply during various seasons.Abbreviations BM body mass - DEI digested energy intake - EWL evaporative water loss - GEL gross energy intake - NH normal hydration - T _a ambient temperature - WR water restriction     

Effect of salt and volume loading on the circulation in the leech,Hirudo medicinalis L.

Summary The effects of increased fluid volume in the closed vascular system on circulation were studied in the leech (Hirudo medicinalis) by intravascular pressure recordings and blood flow measurements.Significant increases in blood volume were achieved by crop loading with hyposmotic (72 mOsmol·kg^–1 H₂O) or hyperosmotic (300 mOsmol·kg^–1 H₂O) salt solutions or by infusion of isosmotic saline (200 mOsmol·kg^–1) into the vascular system.During the high-pressure (HIP) phase, which maintains the rear-to-front circulation, systolic blood pressure in the heart was not affected. An increase in systolic pressure in the heart was observed during the low-pressure (LOP) phase, which supplies the segmental circulation. Heart rate was not changed by crop loading with hyposmotic saline or by vascular infusion. Heart rate decreased after crop loading with hyperosmotic saline. Blood flow rate in the dorsal vessel was increased by crop loading with hyposmotic saline, but not after crop loading with hyperosmotic saline. In all cases the diameter of the dorsal vessel was not affected. A possible mechanism controlling blood pressure and blood flow in the vascular system is discussed.Abbreviations HIP-phase high-pressure phase - LOP-phase low-pressure phase - CNS central nervous system     

Changes in sodium,calcium and magnesium ion concentrations in sturgeon (Huso huso) urine and in kidney morphology

During adaptation to brackish water the young great sturgeon Huso huso is able to regulate its serum osmolarity and ion concentrations. After transfer from fresh water to brackish water the ion concentrations in the urine increase and the urine becomes isoosmotic to the blood serum after 24h. The Na⁺ and K⁺ concentrations in the urine increase during the first 12 h by 4.4 and 7.7 times, respectively, later decreasing again. The Mg²⁺ and Ca²⁺ concentrations in the urine increase by 3.4 and 14 times during the first 72h in brackish water and remain high thereafter. These results suggest that the kidneys play an important part in the regulation of serum osmolarity and in the removal of Ca²⁺; however, in contrast to teleosts, Mg²⁺ must be removed extrarenally. During adaptation to a hyperosmotic medium the diameters of the Malpighian bodies, the glomeruli and the diameter of the tubules initially all decrease, but the distal tubules become morphologically differentiated into two regions and the diameter of the distal section later increases again. It is suggested that this is the site of Ca²⁺ secretion into the urine.     

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     

Ionoregulatory and urinary responses to emersion in the mangrove crab Ucides cordatus and the intertidal crab Carcinus maenas

The mangrove crab Ucides cordatus showed a significant reduction in its output of isosmotic urine (to 60% of submerged rates) in humid, emersed conditions when in apparent water balance. A similar, but lesser, reduction was observed in the intertidal temperature species Carcinus maenas. Some of the decrease is effected by increased water withdrawal of an isosmotic fluid in the antennal gland (inulin urine to haemolymph concentration ratio=1.27) in Ucides but most is due to the reduced filtration rate which decreases from 3.41 to 2.19 ml·100 g^-1·day^-1 (in Carcinus from 7.37 to 5.88). In Carcinus, inulin urine to haemolymph concentration ratios are within the range 1.34–1.41 and show significant change on emersion. Comparisons of ion and inulin clearance ratios revealed interspecific differences in renal handling of Na⁺ and Cl^-. During emersion total Na⁺ efflux is markedly reduced in both species. Urinary Na⁺ losses are responsible for most of the efflux in Carcinus but represent only 50% of the total in Ucides. Significant Na⁺ uptake from interstitial water occurs in Ucides. REductions in ion and water loss appear to be mainly dependent on decreases in urine output (clearance rate). However, some released urine was found to accumulate in the branchial chambers in both species. Whether or not extrarenal reabsorption of ions from released urine occurs in the gill chambers in either crab species remains to be proved.Abbreviations CPM counts per minute - ECF extracellular fluid - k rate constant for inulin clearance - k ^Na rate constant for sodium efflux - J _out ^Na sodium efflux rate - Q _tot total radioactivity injected - SEM standard error of mean - SW sea water - 9-SW sea water, salinity 9 mg·ml^-1 (ppt) - 26-SW sea water, salinity 26 mg·ml^-1 (ppt) - U/B ratio of urine (U) to haemolymph (B) concentrations - V _c1 clearance rate - V _u urine output - V _a inulin space     

Pre-and post-branchial blood respiratory status during acute hypercapnia or hypoxia in rainbow trout,Oncorhynchus mykiss

Simultaneous venous (pre-branchial) and arterial (post-branchial) extracorporeal blood circulations were utilized to monitor continuously the rapid and progressive effects of acute environmental hypercapnia (water partial pressure of CO₂ 4.8±0.2 torr) or hypoxia (water partial pressure of O₂ 25±2 torr) on oxygen and carbon dioxide tensions and pH in the blood of rainbow trout (Oncorhynchus mykiss). During hypercapnia, the CO₂ tension in the arterial blood increased from 1.7±0.1 to 6.2±0.2 torr within 20 min and this was associated with a decrease of arterial extracellular pH from 7.95±0.03 to 7.38±0.03; the acid-base status of the mixed venous blood changed in a similar fashion. The decrease in blood pH in vivo was greater than in blood equilibrated in vitro with a similar CO₂ tension indicating a significant metabolic component to the acidosis in vivo. Under normocapnic conditions, venous blood CO₂ tension was slightly higher than arterial blood CO₂ tension difference was abolished or reversed during the initial 25 min of hypercapnia indicating that CO₂ was absorbed from the water during this period. Arterial O₂ tension remained constant during hypercapnia; however, venous blood O₂ tension decreased significantly (from 22.0±2.6 to 9.0±1.0 torr) during the initial 10 min. Hypercapnia elicited the release of catecholamines (adrenaline and noradrenaline) into the blood. The adrenaline concentration increased from 6±3 to 418±141 nmol · l^-1 within 25 min; noradrenaline concentration increased from 3±0.5 to 50±21 nmol · l^-1 within 15 min. During hypoxia arterial blood O₂ tension declined progressively from 108.4±9.9 to 12.8±1.7 torr within 30 min. Venous blood O₂ tension initially was stable but then decreased abruptly as catecholamines were released into the circulation. The release of catecholamines occurred concomitantly with a sudden metabolic acidosis in both blood compartments and a rise in CO₂ tension in the mixed venous blood only.Abbreviations CCO₂ plasmatotal carbondioxide - CtO₂ blood oxygen content - PO₂ partial pressure of oxygen - PCO₂ partial pressure of carbon dioxide - PaO₂ arterial bloodPO₂ - PaCO₂ arterial bloodPCO₂ - PvCO₂ venous bloodPCO₂ - PwO₂ waterPO₂ - PwCO₂ waterPCO₂ - Hb haemoglobin - SHbO₂ haemoglobin oxygen saturation - HPLC high-performance liquid chromatography - rbc red blood cell(s) - Hct haematocrit     

Adaptation of renal function to hypotonic medium in the winter flounder (Pseudopleuronectes americanus)

Summary The kidneys of winter flounders transferred to hypotonic medium were investigated for glomerular and tubular handling of fluid and electrolytes and for the urinary excretion of proteins. Media were sea water (925 mosm·kg^–1) and brackish water (70 mosm·kg^–1).In sea water, the urine was hypertonic to the plasma in 7 fish of this study. Urine flow rate was correlated with the GFR. After adaptation to brackish water a delay of 1 to 3 days was observed until the kidneys switched from fluid retention to the excretion of large amounts of dilute urine. GFR and urine flow rate were increased from 0.61±0.08 to 1.58±0.29 ml·h^–1·kg^–1 and from 0.14±0.02 to 0.68±0.08 ml·h^–1·kg^–1, respectively . With increased filtered load the tubular reabsorption of fluid decreased from 74±2.4% to 45±11.2%. The excretion rates of sodium and potassium were increased due to decreased fractional sodium and potassium reabsorption. The urinary excretion of divalent cations, however, was reduced because the net tubular reabsorption of calcium was increased and the net secretion of magnesium was diminished.Both the urinary total protein concentration and the protein pattern showed no significant change, but the rate of protein excretion was increased from 0.21±0.04 to 0.60±0.05 mg·h^–1·kg^–1. The comparison of protein patterns obtained from urine and serum samples revealed that high molecular weight (HMW) proteins prevail in the serum whereas low molecular weight (LMW) proteins dominate in the urine. The diminished quantity of the HMW-protein fraction in the urine thus may reflect size selectivity of the glomerular filtration barrier for serum proteins also in the winter flounder.Abbreviations BW brackish water - SW sea water - GFR glomerular filtration rate - HMW heigh molecular weight - LMW low molecular weight     

Ion movements associated with chorion elevation during egg laying in trout (Oncorhynchus mykiss) in fresh water

Within 1 min of transfer from coelomic fluid to fresh water, eggs of rainbow trout (Oncorhynchus mykiss) underwent a transient loss of Na⁺ and K⁺ coupled with an elevation of the chorionic envelope. Both mechanisms were blocked by adding a monovalent cation Li⁺ or K⁺ (140 mmol·l^-1) to the fresh water, but the divalent ion Mg²⁺ (100 mmol MgCl₂·l^-1) or elevating the osmotic pressure to 300 mOsmol·l^-1 with glycine had no inhibitory effect. The blocking of Na⁺ loss occurred at external monovalent cation (LiCl) concentrations above 70 mmol·l^-1. A 20-s exposure of eggs to fresh water was sufficient to trigger Na⁺ loss and chorion elevation, even when the eggs were subsequently transferred to fresh water containing 140 mmol LiCl·l^-1. Eggs placed in a medium containing 140 mmol LiCl·l^-1 and 2 mmol Ca(NO₃)₂·l^-1 showed chorion elevation and associated Na⁺ loss after addition of calcium ionophore (20 mol·l^-1 A.23187). This activation by calcium ionophore was supressed in a Ca²⁺-free medium containing 5 mmol EGTA·l^-1.     

Estimated feeding rates and energy requirements of gentoo penguins,Pygoscelis papua,at Macquarie Island

Summary Water and sodium turnovers of 6–7 week old gentoo penguin chicks and breeding adults were measured using isotopically labelled water and sodium. Influx rates for chicks averaged 188 ml·kg^-1·day^-1 and 13.9 mmol·kg^-1·day^-1 for water and sodium, respectively. Chicks consumed an estimated 228 g·kg^-1·day^-1 fresh food or 886 kJ kg^-1 day. These values correspond to 761 g·day^-1 or 2945 kJ·day^-1 for a gentoo chick mid-way through the growth period. Flux rates for adults attending chicks ranged from 199 to 428 ml·kg^-1·day^-1 for water and from 15 to 36 mmol·kg^-1·ay^-1 for sodium.     

Intestinal nutrient transport in coho salmon (Oncorhynchus kisutch) and the effects of development,starvation, and seawater adaptation

Summary Intestinal nutrient transport in yearling coho salmon was characterized and adaptive changes in nutrient transport were described in relation to development, starvation, and environmental salinity. Salmon intestine exhibits a small transepithelial potential difference (TEP: –1.4 to 2.0 mV, mucosa ground) and low resistance (41 to 181 ohms·cm²) that varied with the region along the intestine, with starvation, and with environmental salinity. Addition of glucose or proline to the mucosal side of intestine caused a rapid increase in short-circuit current. Isotopic mucosalto-serosal net fluxes of glucose and proline were achieved across salmon intestine in the absence of transepithelial chemical or electrical gradients. A sleeve technique for measuring proline influx (Karasov and Diamond 1983a) was validated for use in salmon intestine. Comparison of total proline influx in different intestinal regions showed the following order (from highest to lowest rates): pyloric caeca anterior intestine > posterior intestine. Total proline influx was highest in April during the parr-smolt transformation.The kinetics of Na-dependent proline influx were altered by starvation and seawater adaptation. Starved fish exhibited a lowerK _t but similarJ _max in anterior intestine compared with values in fed fish. The effect of seawater adaptation on the kinetics of proline influx varied with the timing of entry into seawater, with length of seawater residence, and with season. Growth-inhibited SW stunts showed a reducedJ _max of proline influx compared with that of normal SW smolts.Abbreviations FW freshwater (-adapted) - SW seawater (-adapted) - TEP transepithelial potential difference - R transepithelial resistance - I _sc short-circuit current - P _a apparent passive permeability coefficient - J _max maximal influx - K _t half-saturation constant     

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     

Stress response in two Antarctic teleosts (Notothenia coriiceps Richardson andChaenocephalus aceratus Lönnberg) following capture and surgery

Blood chemistry and haematological parameters have been determined in two Antarctic teleosts,Notothenia coriiceps Richardson andChaenocephalus aceratus Lönnberg, held at around 1°C.Notothenia coriiceps has a low haemoglobin content compared to tem-perate-zone species, whereasC. aceratus apparently lacks respiratory pigments. Blood samples were obtained by cardiac puncture following landing or using chronically implanted post-branchial arterial cannulae. Although both species showed a similar acidosis on capture (arterial pH as low as 7.5 versus the final recovery value of around 7.9),C. aceratus took 48 h to reestablish baseline values whileN. coriiceps recovered within 12 h, despite initially showing a greater degree of hypercapnic hypoxia. Surgery led to a more severe disturbance of acid-base regulation inN. coriiceps thanC. aceratus (arterial pH of 7.5 versus 7.8) but needed only half as long for recovery. A progressive decrease in arterial oxygen tension and increase in arterial carbon dioxide tension (both more pronounced inN. coriiceps) with level of acidosis was observed down to arteria pH 7.2 InC. aceratus this was accompanied by a rise in blood lactate (up to 10 mmol·1^-1 in some individuals), whileN. coriiceps showed only a modest and transient lactacidosis. Stress inN. coriiceps therefore induces primarily a respiratory, rather than a metabolic acidosis, whereas inC. aceratus both components are present. A differential response to stress is also indicated by an elevated, though low noradrenaline titre inN. coriiceps following surgery and capture, whileC. aceratus was little affected by surgery. However, both species show an unusually weak catecholamine response to induced stress.Abbreviations pH/T °C thermal sensitivity of pH - Ad adrenaline - bw body weight - C.CO₂ total carbon dioxide content - C.O₂ total oxygen content - ED ₅₀ Median effective dose - EDTA ethylenediaminetertra-acetic acid - Hb haemoglobin - Hct haematocrit - HPLC high-performance liquid chromatography - lac lactate - MCH mean corpuscular haemoglobin content - MCHC mean corpuscular haemoglobin concentration - MCV mean cell volume - MS222 tricaine methane sulphonate - NAd noradrenaline - P _aCO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen tension - pHa arterial blood pH - RBCC red blood cell count - SW sea water - T _a ambient air temperature - VO₂ oxygen consumption     

Activity,milk intake and energy consumption in free-living ringed seal (Phoca hispida) pups

Measurements of growth, activity and energy consumption and estimates of milk intake were made in free-living, nursing ringed seal (Phoca hispida) pups. This was accomplished through the simultaneous use of time-depth recorders and the doubly labelled water technique. The pups spent an average of 52±7% of their time hauled out on the ice, 37±5% of the time in the water at the surface, and 11±5% of the time diving. Average daily mass gain of the pups (n=3) throughout the duration of the study period was 0.35±0.08 kg. The composition of the mass gain was 76% fat, 6% protein and 18% water. The total water flux was measured to be 52±10 ml·kg^-1·day^-1. Average CO₂ production was 0.85±0.16 ml·g^-1·h^-1, corresponding to a field metabolic rate of 0.55±0.10 MJ·kg^-1·day^-1, or 3.8±0.6 times the predicted basal metabolic rate based on body size (Kleiber 1975). Average daily milk intake was estimated to be 1379±390 ml. The field metabolic rate for the different components of seal pup activity budgets were calculated to be FMR_{haul out}=1.34 BMR, FMR_surface=6.44 BMR, and FMR_diving=5.88 BMR.Abbreviations BMR basal metabolic rate - FMR field metabolic rate - HTO tritiated water - HT¹⁸O doubly labelled water - RQ respiration quotient - SDA specific dynamic action - TDR time-depth recorder     

Mediation of serotonin-induced hyperventilation via 5-HT3-receptor in European eel Anguilla anguilla

The effects of serotonin (5-hydroxytryptamine) on ventilation were investigated by continuous measurements of intrabuccal pressure in unrestrained eel. Intravenous administration of 5-hydroxytryptamine (30 g·kg^-1) caused a large increase in ventilatory frequency (+100%) and amplitude (+140%). The 5-hydroxytryptamine-induced hyperventilation was blocked by the 5-HT₃-receptor antagonists metoclopramide (1.0 mg·kg^-1) or MDL72222 (1.0 mg·kg^-1), and was insensitive to the 5-HT_1/2-receptor antagonist methysergide (3.0 mg·kg^-1) and to the 5-HT₄-receptor antagonist DAU 6285 CL (3.0 mg·kg^-1). The hyperventilatory response to 5-hydroxytryptamine could be mimicked by the 5-HT₃ receptor agonist 1-phenylbiguanide (300 g·kg^-1). These results strongly implicate the 5-HT₃-receptor as the mediator of the 5-hydroxytryptamine-induced hyperventilation in eel.Abbreviations a.u. arbitrary units - 5-HT 5-hydroxytryptamine - SEM standard error of mean - VA ventilatory amplitude - VF ventilatory frequency - RBI 1-phenylbiguanide     

Effects of rapid transfer from sea water to fresh water on respiratory variables,blood acid-base status and O2 affinity of haemoglobin in Atlantic salmon (Salmo salar L.)

Summary Oxygen consumption, gill ventilation, blood acid-base/ionic status and haemoglobin oxygen affinity were studied in seawater-adapted adult salmon (Salmo salar) during five weeks after transfer into fresh water. Freshwater exposure induced the following changes: Standard oxygen consumption ( ) and ventilatory flow ( ) decreased markedly during the first days after transfer, then decreased more gradually until a new steady-state was achieved at which and were about 80% and 56% of the control values, respectively. The marked increase in oxygen extraction coefficient (Ew _{O 2}) and the marked decrease in the oxygen convection requirement ( ) were associated with a reduction in the partial pressure of carbon dioxide in arterial blood (Pa _{CO 2}), in spite of a decrease of both ventilatory flow and water CO₂ capacitance. These results suggested that transfer into fresh water induced an increase in branchial diffusive conductance. A biphasic pattern was observed in the time-course of the changes in both plasma ion concentration and acid-base status. During the first 10 days, plasma Na⁺, K⁺, and Cl^– concentrations fell abruptly, then more gradually. [Cl^–] decreased more than [Na⁺] resulting in a progressive increase in the [Na⁺]/[Cl^–] ratio. During the second phase of acclimation to fresh water plasma Na⁺, K⁺, and Cl^– concentrations progressively increased. [Cl^–] increased more than [Na⁺], so that [Na⁺]/[Cl^–] ratio decreased. Transfer into fresh water did not significantly change plasma lactate concentration. Upon exposure to fresh water, blood pH increased from 7.94±0.04 to 8.43±0.06 at day 10 and then decreased to 8.08±0.03 at day 34. The increase in blood pH induced by transfer to fresh water initially represented a mixed metabolic/respiratory alkalosis. However, after 15 days Pa _{CO 2} had returned to pretransfer values and the alkalosis was purely metabolic. The metabolic component of the alkalosis was associated with appropriate changes in the plasma strong ion difference (S.I.D.). Blood alkalosis moved the oxygen dissociation curve to the left, so that P₅₀ was decreased by 30% below the value in seawater for the maximal increase in blood pH. This rise in haemoglobin affinity for O₂, associated with a marked increase in blood buffer capacity, are regarded as adaptative processes allowing the salmon to cope with the markedly increased energy expenditure required for upstream migration.