The metabolic clearance rate and uterine metabolism and retention of progesterone and 20alpha-hydroxypregn-4-en-3-one during the secretion of uteroglobin in ovariectomized, steroid-treated rabbits.

The metabolic clearance rate (MCR) and in vivo uterine metabolism and retention of progesterone (P) and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OHP) during the uterine synthesis of uteroglobin in the rabbit have been studied. Oophorectomized rabbits with the uteri ligated received daily im injections of oil vehicle (C), 2 mg P/kg BW, or 2 microgram estradiol/kg BW. The MCR of [14C]P and [3H]20 alpha-OHP did not differ among treatment groups and was 260 +/- 30 and 270 +/- 33(SE) liters/day, respectively. Although the uterine tissue to arterial blood ratio of [14C]P differed between groups (E greater than C greater than P), the tissue to blood ratio of 20 alpha-OHP was the same for the three groups and was about 1. The uterine extraction of P was 32 +/- 6.2(SE)% and was the same for the three treatment groups. The uterine extraction of 20 alpha-OHP was significantly increased by estrogen treatment [33.4 +/- 6.0(SE)%] compared to the control [14.8 +/- 3.3(SE%)] or P[16.9 +/- 4.5(SE)%] groups. These studies indicate that the ability of exogenous 20alpha-OHP to stimulate uteroglobin secretion is probably mediated by its peripheral conversion to P. These studies also indicate the value of continuous infusion of radioactive steroids to evaluate tissue retention and metabolism in vivo.