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.