PROGESTERONE AT PLASMA-LEVELS LOWER THAN THOSE OF MID-PREGNANCY DECREASES SEXUAL-BEHAVIOR IN OVARIECTOMIZED RATS

Progesterone was measured by radioimmunoassay in the plasma of Day 10 pregnant rats and in the plasma of ovariectomized rats injected with doses of progesterone that result in a decrease in sexual receptivity. Doses of progesterone (1-2.5 mg) that result in behavioral refractoriness to further progesterone treatment result in lower plasma levels of progesterone than those measured on the tenth day of pregnancy, a time of naturally-occurring behavioral inhibition. These data re-assert the possibility that endogenous progesterone produced during pregnancy in the rat is at least partially responsible for the decrease in female sexual behavior seen during pregnancy in this species. © 1979.