STEROID DYNAMICS IN THE RABBIT

Male rabbits were infused at a constant rate with 3H-androstenedione/14C-estrone (n = 5) or 3H-testosterone/14C-estradiol-17.beta. (n = 3) for 3.5 h, and blood samples were obtained over the last hour and analyzed for radioactivity as androstenedione (A), testosterone (T), estrone (E1), estradiol-17.beta. (E2.beta.) and estradiol-17.alpha. (E2.alpha.). The mean value for the metabolic clearance rate of androstenedione (MCRA) was 85 .+-. 10 l/day per kg, which was significantly greater than the mean MCRE1 59 .+-. 10 l/day per kg. MCRT, 42 .+-. 8 l/day per kg, and MCRE2.beta., 45 .+-. 9 l/day per kg were not different. The conversion ratio of androstenedione to testosterone (CRA,T) was greater than CRT,A but for the estrogens, CRE2.beta.,E1 was greater than CRE1,E2.beta.. CRE2.beta.,E2.alpha. was greater than CRE1,E2.alpha.. The overall aromatization of androstenedione to estrone, the fraction of 3H-androstenedione infused into the blood and measured as 3H-estrone in blood .**GRAPHIC**. was 0.0005 .+-. 0.0001 and for .**GRAPHIC**. was 0.0012 .+-. 0.0006. In the rabbit both sex hormone binding globulin (SHBG) and albumin binding may effect the MCR, and peripheral aromatization of androgens occurs to a far lesser degree than in humans and primates.