Renal effects of atrial natriuretic factor in domestic fowl

The renal hemodynamic and tubular effects of ANF were investigated using the Sperber technique in chickens. This technique takes advantage of the unique portal circulation of the avian kidney and permits direct access to the renal peritubular space independent of renal arterial blood flow and glomerular filtration. Infusion of ANF into the avian renal portal system increased urine flow rate and sodium excretion by as much as 300% and 100%, respectively. These changes occurred in the absence of significant alterations in glomerular filtration rate or renal plasma flow. There was no significant difference in urine flow, sodium excretion or glomerular filtration rate between the ANF-infused kidney and the contralateral, non-infused kidney. We conclude that the diuretic and natriuretic effects of ANF do not depend on changes in glomerular filtration rate and that the site of action of ANF is the renal medulla.     

Effect of dietary energy intake on tubular reabsorption of urea in sheep

The aim of the experiment was to determine the effect of dietary energy intake on renal urea excretion in sheep with different nitrogen intakes. The control sheep, with a high nitrogen and energy intake, were given a daily feed dose of 21.18 g N and 15.2 MJ digestible energy (DE). The two experimental groups, with an equal, low nitrogen intake, were given diets with a different energy content. The high energy diet contained 3.63 g N and 14.18 MJ DE, the low energy diet 3.4 g N and 6.44 MJ DE. After nine weeks' adaptation to the diets, renal functions were measured by a standard clearance technique. It was found that, under stable urine flow conditions, both groups given the low nitrogen diet had a significantly lower glomerular filtration rate, fractional urea excretion and total urea excretion. A reciprocal comparison of these two groups showed that fractional urea excretion by the sheep with a high energy intake was significantly lower than in the group with a low energy intake. There were no differences in the glomerular filtration rate. A raised dietary energy intake in the presence of a low nitrogen intake caused marked natriuresis and kaliuresis. The results indicate that a raised dietary energy intake can be a significant factor in potentiating the renal effect of urea retention in sheep with a low nitrogen intake.     

Dietary sodium,glomerular filtration rate autoregulation,and glomerular size distribution profiles in domestic fowl (Gallus gallus)

Summary Mammalian glomerular filtration rate (GFR) autoregulation can be impaired by protocols that inhibit tubuloglomrular feedback, such as high sodium intake. Domestic fowl were fed diets containing either high sodium (0.39% Na: High-Na Group) or low sodium (0.03% Na: Low-Na Group). An arterial snare was used to reduce renal arterial perfusion pressure (RAPP) in a stepwise fashion to evaluate GFR autoregulation. Absolute sodium excretion, fractional sodium excretion (FE_Na), and ambient systemic arterial blood pressure were significantly elevated in the High-Na Group when compared with the Low-Na Group, and pressure natriuresis was abolished by the Low-Na diet. However, GFR autoregulatory profiles were identical in birds fed High-Na and Low-Na diets, suggesting that tubuloglomerular feed-back does not contribute significantly to avian GFR autoregulation. Filtering glomeruli were stained in vivo with alcian blue dye to determine if RAPP-induced reductions in GFR are associated with cessation of filtration (glomerular intermittency) by a portion of the nephron population. RAPP was held below the GFR autoregulatory range (experimental group) or was at ambient systemic arterial pressure (control group) during glomerular staining. Reducing RAPP below the autoregulatory range reduced GFR by 50%, but similar glomerular size distribution profiles were observed for experimental and control groups. These results indicate that sustained glomerular intermittency does not contribute to the decrease in GFR when RAPP is reduced below the autoregulatory range.Abbreviations BW body weight - C control - E excretion - FE fractional excretion - FF filtration fraction - GFR glomerular filtration rate - PAH p-amino hippuric acid - RAPP renal arterial perfusion pressure - RPF renal plasma flow - RT reptilian-type - SNGFR single nephron glomerular filtration rate - U _OSM urine osmolarity - UFR urine flow rate     

Early changes in renal function following chemically induced nephropathy

The functional changes in the rat kidney 24 h after administration of 2-bromoethanamine hydrobromide (BEA) have been extensively described. There is, however, little information regarding earlier alterations. The present study was designed to measure early changes in renal function in order to clarify further pathomechanisms of the BEA-induced lesion. Experiments were performed in two groups of Wistar rats with different infusion rates during the first 3 h following injection of 100 mg/kg BW BEA compared to sham-injected rats. Analysis included measuring urine flow, osmolality, urea, sodium and potassium as well as inulin and para-aminohippuric acid clearance. Our studies show a tubular as well as a glomerular involvement in BEA-induced nephropathy. A significantly higher urine flow occurred already in the first 30 min following injection of BEA. Urine osmolality began to decrease after 90 min, Na excretion was elevated at 3 h, K excretion was not significantly different from the control group, urea excretion was increased after 30 min. Contrary to other studies we found a continuously decreasing glomerular filtration rate and PAH clearance during the first 3 h. Our results suggest an early effect of BEA on tubular function (increasing sodium excretion), papillary concentration capacity (increasing urine flow combined with decreasing osmolality) and glomerular function (decreasing glomerular filtration rate).     

The renal response to the ingestion of fluid by the fetal sheep

To see if the variability in fetal urine flow and sodium excretion was related to fetal drinking activity, renal function was investigated in two groups of oesophageally-ligated fetuses and one group of non-ligated fetuses. There was no significant difference in urine flow, sodium excretion or glomerular filtration rate in the ligated fetuses compared with the non-ligated fetuses. Furthermore, oesophageal ligation had no effect on the variability in urine flow and sodium excretion rate. The response of fetal kidney to ingestion of fluid was investigaeed in 2 groups of oesophageally-ligated fetuses. In one group it was shown that ingestion of 20 ml/kg of amniotic fluid by the fetus had no consistent effect on fetal renal function. In the other group it was shown that the ingestion of 200 ml water also had no consistent effect on fetal renal function. The water load caused a rise in fetal blood pressure and a fall in plasma osmolality. Since there was no significant increase in free water clearance and fetal plasma osmolality decreased then rose towards control levels, it is concluded that the oral water load was absorbed from the fetal gastrointestinal tract and diffused out of the fetal compartment across the placenta. These experiments show that fetal drinking is probably not responsible for the variability often seen in fetal urine flow and sodium excretion rate.     

The effect of dipyridamole on the initiation phase of postischemic acute renal failure in rats

Several previous observations support the hypothesis that increased adenosine production and release mediate, at least in part, the reductions in renal blood flow and glomerular filtration rate in ischemic acute renal failure (ARF). If this hypothesis is correct, dipyridamole should potentiate these changes, since it blocks cellular adenosine uptake, thereby increasing the concentration and potentiating the effects of extracellular adenosine. Moreover, theophylline should block the effects of dipyridamole, since it is an adenosine receptor antagonist. These predictions were tested in three groups of anesthetized rats. All rats were subjected to 30 min of left renal artery occlusion; 30 min after relieving the occlusion, a 45-min clearance period was begun. The control group was given saline i.v.; the two experimental groups received either dipyridamole (24 micrograms X min-1 X kg-1) or dipyridamole plus theophylline i.v. (111 mumol/kg as a prime, 1.1 mumol X min-1 X kg-1 as an infusion). In the control group, the previously ischemic left kidneys exhibited decreased clearances of para-aminohippurate and inulin (CPAH and CIn), filtration fraction (FF), and urine/plasma inulin concentration (U/PIn), and increased urine flow (V), Na excretion (UNaV), and fractional Na excretion (FENa) in comparison with the contralateral right kidney. Dipyridamole pretreatment did not affect the right kidney, but it intensified the reductions in left kidney CPAH, CIn, and FF. Theophylline blocked all these effects of dipyridamole on the left kidney, and increased renal plasma flow (CPAH/PAH extraction), despite a decrease in systemic arterial blood pressure. These results are further support for the hypothesis that adenosine mediates, at least in part, the hemodynamic changes in postischemic ARF in rats.     

Water diuresis from clonidine (catapres).

The renal hemodynamic and excretory effects of clonidine were tested in two groups of dogs. In one group, the drug was given directly into the renal artery at a rate of 1.2 mug/min and resulted in a significant decrease of the effective renal plasma flow (ERPF) in both kidneys, an increase in filtration fraction (FF), urine volume (UV), and free water clearance (CH2O) and had no effect upon the glomerular filtration rate (GFR), osmolar clearance (Cosm) and the excretion of sodium (UNaV), chloride (UC1V), potassium (UKV), calcium (UCaV) and phosphorous (UPO4V). No unilateral effect was appreciated. In the second group of animals it was given intravenously at a rate of 12.0 mug/min and resulted in a significant decrease of ERPF, UNaV, UC1V, and increase in FF, UV, and CH2O) but had no effect upon GFR, Cosm, UKV, UCaV and UPO4V. Systemically it decreased heart rate (H.R.) and respiratory rate (R.R.) in both groups of animals; it increased blood pressure (BP) in Group 1 and had no effect on BP in Group 2.     

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     

The effect of vasopressin upon the excretion of calcium by the sheep.

Vasopressin (140 muU/min) was infused intravenously into 12 conscious merino ewes for 2 hr. Urine flow rate and free water clearance were consistently reduced. There was no effect upon renal plasma flow, glomerular filtration rate or the rate of excretion of sodium, potassium, magnesium, chloride or phosphate. Although all animals received 75 mmol calcium chloride into the rumen on the previous day, five commenced the experiment with calcium excretion rates of less than 1 mumol/min. In these, vasopressin further decreased calcium excretion. In seven animals with calcium excretion rates between 2 and 20 mumol/min vasopressin had no effect upon either total calcium or free ionized calcium excretion rate.     

High urine flow rate increases prostaglandin E excretion in the conscious dog

Although previous studies from this and other laboratories have shown that urinary prostaglandin E excretion (U_PGEV) can vary independent of urine flow rate, recent studies during water diuresis in the conscious dog have suggested that high urine flow rate per se may increase U_PGEV. To examine the effect of urine flow rate on U_PGEV we administered either mannitol, chlorothiazide or Ringer's solution to mongrel dogs and measured U_PGEV. During anesthesia neither mannitol or chlorothiazide increased U_PGEV. There was, however, a consistent increase with all three agents in awake animals. This increase in U_PGEV was independent of alterations in glomerular filtration rate. There was a consistent increase in urinary sodium excretion and decrease in urinary osmolality with all three agents. The changes in PGE, however, were similar to those found during water diuresis when no increase in sodium excretion was found. It is not presently clear whether these findings reflect a true increase in renal PGE synthesis due to some change in flow or pressure within the renal medulla or rather represent unchanged PGE synthesis by renal tubular cells, the high tubule fluid flow rate causing increased entry into the tubular lumen in contrast to the renal interstitium.     

Glomerular function in spontaneously diabetic rats.

This study was undertaken to determine whether hyperfiltration exists at the single nephron level and whether albumin excretion is increased early in the course of diabetes in Biobreeding rats. Diabetic rats were studied at 8-12 weeks after the onset of diabetes. Control animals were age-matched, diabetes-resistant rats. Urinary and tubular fluid albumin concentrations were measured by polyacrylamide gel electrophoresis. Clearance and micropuncture techniques were used to determine whole kidney and single nephron glomerular filtration rate, renal blood flow, and glomerular capillary pressure. The urinary albumin excretion rate (1.3 +/- 0.1 mg/24 hr) and the tubular fluid albumin concentration (4.7 +/- 0.7 mg/dl) in the diabetic group were significantly elevated when compared with urinary albumin excretion (0.9 +/- 0.1 mg/24 hr) and tubular fluid albumin concentration (2.5 +/- 0.5 mg/dl) in the control group. There were no significant differences in glomerular hemodynamics (whole kidney or single nephron glomerular filtration rate or glomerular capillary pressure) between diabetic and control rats. The kidney weight and kidney weight to body weight ratio were significantly higher in diabetic rats when compared with control rats. Early diabetes in Biobreeding rats is characterized by mild albuminuria and increased kidney size, but not glomerular hyperfiltration.     

The influence of renal function on lactate and glucose metabolism.

The relationship of lactate metabolism to renal function was studied in the isolated perfused rat kidney. A new radioisotopic method has been developed that enables the simultaneous measurement of lactate production and consumption in the presence of physiological concentrations of both lactate and glucose. In kidneys from fed rats, when glucose was absent, lactate production was only 12 mumol/h per g dry wt, and in kidneys from starved rats there was no lactate production, indicating that neither the phosphoenolpyruvate/pyruvate substrate cycle nor other analogous cycles for the recycling of lactate carbon are operating in the intact kidney cortex. Lactate production from glucose occurred at a high rate, at the same time as lactate consumption, demonstrating that lactate recycling between renal cortex and medulla can occur in the intact kidney. Lactate production from glucose correlated with glomerular filtration rate (P less than 0.001), urine flow rate (P less than 0.01) and sodium reabsorption (P less than 0.05). There was significant basal lactate production at zero glomerular filtration rate. Lactate consumption was not correlated with any renal function. When Na+ reabsorption was inhibited with the diuretic frusemide, or when filtration was entirely prevented (the 'non'-filtering kidney'), lactate production was decreased by 39% and 50% respectively. Basal lactate production determined in this way was the same as that calculated above by linear regression. Prevention of filtration, but not the addition of frusemide, significantly inhibited lactate consumption. It is concluded that glycolysis is required for medullary Na+ transport, and that some different transport function(s) require lactate oxidation.     

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     

Glomerular intermittency in a freshwater teleost,Carassius auratus gibelio,after transfer to salt water

Summary Alcian blue (AB) was applied intravenously to cannulated, conscious Prussian carp. The glomeruli exhibited selective staining with AB. Electronmicroscopy of the filtration barrier revealed dense deposits of AB in the epithelial and endothelial cell coats and in the glomerular basement membrane. The total number of stained glomeruli per kidney was 14,170±578 in fresh water carp, and 6,437±2,114 in carp-adapting to isotonic saltwater . The number of stained glomeruli can be correlated with the urine flow (r=0.79,n=10,P<0.01). In saltwater fish the urine flow was significantly lower than in the fresh water controls (P<0.01). It is concluded that glomerular intermittency is involved in the control of urine flow in this teleost.     

Germanium in ginseng is low and causes no sodium and water retention or renal toxicity in the diuretic-resistant rats

Ginseng preparations contain high concentrations of germanium (Ge), which was reported to contribute to diuretic resistance or renal failure. However, Ge content in ginseng and the influence on renal functions remain unclear. Forty rats were randomly divided into control group, low, moderate, and high Ge ginseng-treated group and observed for 25 days. Daily urine, renal functions, and serum and urine electrolytics were measured. Ge retention in the organs and renal histological changes were also evaluated. Ge content ranged from 0.007 to 0.450 µg/g in various ginseng samples. Four groups showed no difference in the daily urine output, glomerular filtration rate, urinary electrolytes excretions, 24 h-urine protein, as well as plasma and urine urea nitrogen, creatinine, osmotic pressure, and pH values. Ge did not cause any renal pathological effects in this study. No Na and water retention was detected in the ginseng-treated groups. Ge retention in various organs was found highest in spleen, followed by the kidney, liver, lung, stomach, heart, and pancreas. The total Ge contents in various ginsengs were low, and ginseng treatment did not affect renal functions or cause renal histological changes.     

Seasonal changes in glomerular filtration rate in Antechinus stuartii (Marsupialia: Dasyuridae)

The small marsupial Antechinus stuartii experiences a synchronised life cycle that culminates in complete male mortality (within 3 weeks) following the 1 week mating period in mid-August (late winter). There are pronounced physiological changes in male A. stuartii over the life cycle and renal function was assessed for correlation with these changes. Glomerular filtration rate and urine and plasma electrolytes were determined in male and female A. stuartii in February, May, July and August. Females showed little change in glomerular filtration rate, except for pre-mating values in August which decreased. In contrast, glomerular filtration rate of males decreased significantly in July and August. Plasma sodium and chloride levels were higher in males than females and were higher in animals in July and August than in February and May. Plasma potassium levels dropped in both males and females in July and August. Plasma osmolality was higher in animals in February compared to animals from May and August. However, there were no significant sex or seasonal differences in urine electrolytes, although urea concentration was higher in females than males. Urine osmolality was higher in both sexes in July and August. There were no significant differences in total excretory rates of sodium, potassium or chloride between sexes or between seasons. Many of the alterations in renal function are correlated with known physiological and hormonal profiles in A. stuartii. This is the first observation of seasonal changes in glomerular filtration rate that are unrelated to dietary and water stresses. Accepted: 8 September 1997     

Effect of temperature on osmotic and ionic regulation in goldfish,Carassius auratus L.

Summary Urine flow increased with acute temperature increases and showed temperature acclimation. When measured at 20 °C the urine flow of 10 °C acclimated fish was 3.2 times greater than the urine flow of 30 °C acclimated fish. In fish acclimated to 24 °C renal reabsorption of Na and Cl was independent of temperature over an intermediate range of temperatures (14–24 °C) but near the lower lethal temperature (6.5 °C) renal Na and Cl reabsorption was inhibited. Water permeability of the renal tubules was not affected by acute temperature change between 6.5 and 24 °C. Urine osmolality and urine Na, K and Cl concentrations showed nearly perfect temperature compensation in fish acclimated to 10 °C and 30 °C. The rate of renal excretion of Na and Cl showed temperature acclimation in that Na and Cl ecxretion measured at 20 °C was 7 to 8 times greater in 10 °C acclimated fish than in 30 °C acclimated fish. The rate of excretion of Na and Cl measured at 30 °C in 30 °C acclimated fish was approximately 1.7 times the rate of excretion measured at 10 °C in 10 °C acclimated fish.The branchial uptake of Na, measured in tap water, of fish acclimated to 10, 20 and 30 °C in demineralized water increased with acute increases in temperature. When the three acclimation groups were compared at an intermediate temperature (20 °C), the 10 °C acclimated group showed the highest rate of net uptake, and the 30 °C group the lowest rate of uptake. This apparent temperature acclimation of Na uptake was correlated with differences in the plasma Na concentration of the three acclimation groups. Plasma Cl concentrations were also correlated with acclimation temperature in fish acclimated in demineralized water, but the rate of net Cl uptake was considerably less than that for Na. Sodium and Cl uptake in fish which had been acclimated in tap water was very variable and was not clearly affected by acute changes in temperature. Uptake of Na and Cl by fish held in tap water did not show temperature acclimation. The difference between uptake and excretion of fish acclimated in tap water was not significantly different from zero, indicating that the fish were in salt balance.The study was supported by National Institutes of Health Grant GM 16932-02 to Dr. Bodil Schmidt-Nielsen. I am grateful to Dr. Schmidt-Nielsen for many useful discussions during the course of this work.     

Inhibition of platelet-activating factor induced renal hemodynamic and tubular dysfunctions with L-655,240, a new thromboxane-prostaglandin endoperoxide antagonist

The continuous infusion or bolus injection of the platelet-activating factor (PAF) is associated with profound hypotension, marked reductions of renal plasma flow, glomerular filtration, and urinary sodium excretion. All these effects are inhibited by blocking PAF receptors. To examine further the potential mediators of PAF on renal function, we utilized L-655,240 (6 mg/kg, intravenously), a thromboxane-prostaglandin endoperoxide antagonist, to study the systemic and renal response to PAF (0.8 micrograms/kg, intravenously) in the anesthetized dog, using clearance methodology. PAF decreased blood pressure from 115 +/- 7 to 54 +/- 4 mmHg (1 mmHg = 133.3 Pa), renal plasma flow from 105 +/- 6 to 74 +/- 56 mL/min, and glomerular filtration from 43 +/- 3 to 32 +/- 1 mL/min. PAF also reduced urine volume from 1.1 +/- 0.2 to 0.4 +/- 0.1 mL/min, and urinary sodium from 158 +/- 7 to 86 +/- 7 mu equiv./min. L-655,240 alone had no significant effect on blood pressure, renal plasma flow, and filtration rate, at any dose. However, the 6-mg/kg dose resulted in a slight elevation of diuresis, from 1.1 +/- 0.2 to 1.9 +/- 0.1 mL/min, and urinary sodium, from 134 +/- 13 to 212 +/- 19 mu equiv./min. All doses of L-655,240 blocked the effect of PAF on blood pressure. However, the two lower doses of this antagonist (1 and 3 mg/kg) failed to prevent the PAF-induced fall of renal plasma flow and filtration rate, and attenuated the effect on urinary sodium in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)     

Renal actions of atrial natriuretic peptide on the postischemic kidney

The objective of this study was to evaluate the renal actions of atrial natriuretic peptide (ANP) in the unilateral postischemic kidney of anesthetized dogs with a severe reduction in glomerular filtration rate. The dose of atrial natriuretic peptide (50 ng.kg-1.min-1) we gave did not alter the mean systemic arterial pressure, renal blood flow, and glomerular filtration rate in the normal kidney, as determined in foregoing studies. ANP was infused into the intrarenal artery continuously for 60 min after the release from 45 min of complete renal artery occlusion. In the vehicle-infused group, the glomerular filtration rate fell dramatically (6% of control), the renal blood flow decreased (60% of control), and the mean systemic arterial pressure tended to increase (136% of control). The urine flow rate and urinary excretion of sodium decreased significantly (25 and 25%, respectively) at 30 min after reflow in the postischemic period. Continuous renal artery infusion of ANP resulted in a marked increase in urine flow rate (246% of control) and the urinary excretion of sodium (286% of control). The administration of ANP led to an improvement in renal blood flow (99% of control) and glomerular filtration rate (40% of control), and attenuated the rise in mean systemic arterial pressure (109% of control), compared with findings in the vehicle-infused group. Plasma renin activity and prostaglandin E2 concentration in the renal venous blood were elevated after the release from complete renal artery occlusion in both groups. These results indicate that the vascular effects of ANP on the postischemic kidney were enhanced and that the peptide maintained the natriuretic effect.     

Head-down tilt and restraint on renal function and glomerular dynamics in the rat

A model utilizing 25 degree head-down tilt (HDT) and incorporated with chronic catheterization and renal micropuncture techniques in rats was employed to study alterations in renal function induced by HDT. Renal function and extracellular volume measurements were performed after 24 h, 4 days, and 7 days of HDT in conscious rats and compared with their own control measurements and to nontilted but similarly restrained rats. After 24 h HDT, glomerular filtration rate (GFR) increased 19 +/- 8% and renal plasma flow (RPF) increased 18 +/- 8% with increases in urine flow rate, Na+, and K+ excretion in conscious rats. These increases after 24 h were associated with an increase in extracellular volume of 16 +/- 3% (P less than 0.01). In the nontilted controls, there was a decrease in extracellular volume after 24 h of suspension. After 7 days of HDT, GFR was decreased by 7 +/- 1% (P less than 0.01), but RPF and extracellular fluid volume were not different from control values. However, RPF and GFR increased in the nontilted rats after 7 days. After 7 days of HDT renal micropuncture studies demonstrated that single-nephron filtration rate was also decreased from 43 +/- 2 to 31 +/- 3 nl/min (P less than 0.05) due solely to reductions in the glomerular ultrafiltration coefficient (0.11 +/- 0.01 to 0.07 +/- 0.01 nl.s-1 X mmHg-1, P less than 0.05). There was a dissociation between GFR and water and Na+ excretion at days 4 and 7 of HDT not observed in the nontilt restraint controls.