Creatinine and inulin clearances were compared in anesthetized male and female rats. Continuous intravenous infusion, midpoint arterial blood sampling, and ureteral catheterization aided accurate measurements. Average inulin clearances were 1.0 ml/min per 100 g. In the control male rat the creatinine clearance persistently exceeded that of inulin. The elevated CCr: CIn ratio could be reduced to 1 by probenecid, PAH, mercury, or high plasma levels of creatinine. In females a single intramuscular dose of testosterone elevated the ratio to that seen in male rats. This effect declined within 6 hr. Manipulations with steroids other than testosterone did not affect results in either sex. It is suggested that male rats secrete creatinine under the influence of androgens and that inulin is therefore a better measurement of the glomerular filtration rate in the male rat.

Renin activities were measured in plasma from an artery and from the hepatic, portal, and renal veins of anesthetized dogs. A significant arterialhepatic venous renin difference was observed during control periods and after elevation of arterial renin by stimulation of endogenous renin secretion (induced by acute salt depletion) or by infusion of exogenous renin. There was good quantitative agreement between the calculated rates of renin infusion and hepatic renin clearance. No significant arterial-portal venous renin difference was observed. Infusion of exogenous renin decreased the usual renal venous-arterial renin difference; slight net renal inactivation of renin was observed in only 2 of 12 periods. We conclude that the liver is the major site of renin inactivation.ADDITIONAL KEY WORDS angiotensin kidney spleen pancreas chlormerodrin gastrointestinal tract sodium depletion liver function anesthetized dogs A renin-like enzyme in normal human urine. Lancet 2: 707, 1964. 14. DE CHAMPLAIN, J.: Studies on the renin-angiotensin system in various human physiological and pathological states.

SUNMMARY1. 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.

Understanding reticulorumen motility is important to the assessment of ruminant health and optimal production, and in the recognition, diagnosis, and treatment of disease. Accordingly, the teaching of reticulorumen motility is a staple of all veterinary curricula. This teaching has historically been based on written descriptions, line drawings, or pressure tracings obtained during contraction sequences. We developed an animated model of reticulorumen motility and hypothesized that veterinary students would prefer use of the model over traditional instructional methods. First-year veterinary students were randomly allocated to one of two online learning exercises: with the animated model (Group A) or with text and line drawings (Group B) depicting reticulorumen motility. Learning was assessed with a multiple-choice quiz and feedback on the learning alternatives was obtained by survey. Seventy-four students participated in the study, including 38/42 in Group A and 36/36 in Group B. Sixty-four out of 72 students (89%) responded that they would prefer use of the animated model if only one of the two learning methods was available. A majority of students agreed or strongly agreed that the animated model was easy to understand and improved their knowledge and appreciation of the importance of reticulorumen motility, and would recommend the model to other veterinary students. Interestingly, students in Group B achieved higher scores on examination than students in Group A. This could be speculatively attributed to the inclusion of an itemized list of contraction sequences in the text provided to Group B and failure of Group A students to read the text associated with the animations.

The exogenous creatinine: inulin clearance ratio was measured in a series of human subjects to determine whether or not a sex difference existed in the renal tubular handling of creatinine. The average clearance ratio was 1.25 and was not affected by the sex of the subject, nor in women, by the phase of the menstrual cycle, nor the complete absence of the adrenal glands. It is concluded that a species difference exists in the renal tubular handling of creatinine, as these findings contrast sharply with the results seen in rats and dogs.