Rate of ovarian progesterone secretion and peripheral plasma progesterone levels in unilaterally ovariectomized, pregnant rats.

Abstract

Peripheral plasma progesterone concentrations were serially examined in 4 sham-operated and 5 intact rats (controls) and in 5 rats that were unilaterally ovariectomized on Day 8 of gestation. The characteristic rise in progesterone levels after Day 10 appeared to be delayed by 2 days in unilaterally ovariectomized rats but by Day 16 their levels were nearly normal. In a separate experiment a venous outflow technique was used to measure the rate of progesterone secretion from one ovary on Day 16 of gestation of 9 intact rats and the remaining ovary of 5 rats, unilaterally ovariectomized 8 days earlier. The rate of progesterone secretion was almost doubled in the unilaterally ovariectomized rats due to a substantial increase in arterio-venous different in plasma progesterone levels but no change in ovarian blood flow. This doubling was sufficient to explain the maintenance of peripheral plasma progesterone levels in unilaterally ovariectomized rats without postulating increased secretion from other organs or a decrease in metabolic clearance rate of progesterone.