The action of pitressin on solute permeability of the rabbit nephron in vivo

The isotopic equilibration of urea, thiourea, and inulin between urine and plasma was determined in rabbits in the presence or absence of antidiuretic hormone (ADH). Animals were anesthetized with ethanol and permitted to reach steady state after completion of surgery. Tracer was then administered by intraarterial infusion in such a manner that a high constant specific activity in plasma was rapidly attained. Urine flow was kept independent of ADH by addition of mannitol. Urea/creatinine clearance ratios and the accumulation of urea in renal medulla and papilla also remained unaffected by ADH. Under these conditions, thiourea and inulin at all times approached equilibrium, at similar rates. In the absence of ADH, urea also equilibrated at a rate similar to that of inulin. The addition of ADH, however, significantly prolonged the delay before urinary urea reached the high constant specific activity of plasma urea. These observations are interpreted in terms of a specific effect of the hormone on the solute permeability of the nephron.

The effect of androgenic hormones on creatinine secretion in the rat

1. The stop flow procedure was used to compare the urinary creatinine: inulin ratios in male and female rats; to confirm previous evidence for secretion of creatinine by the renal tubule in the male rat, and to assess the effect of androgenic hormones on this property of the renal tubule in the female rat.2. The creatinine:inulin ratios in free flow and all stop flow samples in the female rat were close to unity, confirming the absence of secretion of creatinine.3. In the male rat the ratios in the free flow samples exceeded 1.2. In samples proximal to the sodium minimum the ratio rose to a peak of 1.56, and then declined to the free flow level.4. Female rats pre-treated with androgenic hormones exhibited a male type pattern. A single intramuscular dose of testosterone, or daily injections of progesterone for 1 month, had a similar effect. The free flow ratios rose to 1.2 and on stop flow a proximal secretory peak was seen.5. Two conclusions may be drawn-the creatinine clearance is a valid measure of glomerular filtration rate in the female rat, but not in the male; and the secretion of creatinine is a function of the proximal tubular cells which can be influenced by androgenic hormones in the rat.

Renal excretion of inulin, creatinine and ferrocyanide, at normal and reduced clearance levels in the dog

In 54 control periods in 15 normal (anesthetized) dogs, the ratios of the clearances of creatinine and ferrocyanide to inulin (Ccr/Cin and Cfer/Cin) differed significantly from unity, averaging 0.936 ± 0.047 and 0.932 ± 0.059, respectively. However, in these animals, clearance ratios did not vary with Cin, or urine flow, provided that Cin exceeded 2.3 ml/min/kg (lower limit of ‘normal’). In these 15 dogs, Cin varied directly with perfusion pressure, when the latter was transiently reduced by either hexamethonium, hemorrhage or aortic occlusion. Values for Cin below 2.3 ml/min/kg were associated with decreased ratios for Ccr/Cin and Cfer/Cin. This phenomenon was uninfluenced by phloridzin or probenecid, was potentiated by urinary concentration, and (at low clearance levels) was obliterated by elevating urine flow relative to Cin. Clearance deficits quickly and permanently disappeared when Cin was elevated above 2.3 ml/min/kg by restoration of perfusion pressure. Aberrant clearance ratios cannot easily be attributed to tubular damage because they were so promptly and permanently reversed, no histological evidence of immediate or delayed tubular necrosis followed their demonstration, and in six dogs with frank tubular necrosis following HgCl2, or clamping the renal artery, no clearance deficits accompanied comparable reductions in clearance level. The observed direct relationship between clearance ratios and Cin or urine flow, must therefore reflect partial permeability of the normal renal tubule allowing passive back diffusion of at least creatinine and ferrocyanide. In the normal dog, clearance values should probably be interpreted with caution at levels for Cin below 2.0 ml/min/kg.