The metabolic clearance rate of progesterone in the pregnant rhesus monkey.

Abstract

The metabolic clearance rate (MCR) of progesterone was estimated by a single injection technique utilizing [4-14C]progesterone. Intact rhesus monkeys (Macaca mulatto) were studied on days 22, 48, 100 and 155 of gestation and during the follicular phase of the menstrual cycle. Animals unilaterally ovariectomized prior to the fertile cycle were also examined on days 22 and 48 of pregnancy. The disappearance of [14C]progesterone from the circulation consisted of 2 components, an initial phase during which the steroid disappeared rapidly from the circulation, t½(AA), followed by a slower rate of disappearance, T½(BA)- While t½(AA) in intact monkeys did not change during gestation, t½(BA) rose from 17.2 min (day 22) to 29.6 min (day 48), but by day 100 had declined to 15.3 min with no subsequent change throughout the remainder of pregnancy. The absolute MCR of progesterone (1 whole blood/day) in these animals did not vary during pregnancy, but when calculated on the basis of body weight, MCR declined steadily ...