Induction of estrus in female mice: Estrogen-progesterone interactions

Abstract

Accumulating evidence indicates that progesterone can have biphasic, facilitatory and inhibitory, effects on sexual receptivity in the guinea pig and rat. The present study sought to extend the generality of this work to the female mouse. The data indicated that 24 hr following the facilitation of the induction of sexual receptivity in estrogen-primed females by an injection of progesterone, a second injection of progesterone was relatively ineffective in inducing a second period of receptivity. The magnitude of this inhibitory effect appeared to be a function of dose of estrogen priming, with the greatest inhibition occurring in groups primed with relatively low doses of estrogen. The postreceptivity refractoriness was not due to a reduction in the effect of estrogen priming, nor could it be attributed to the effects of repeated testing. Thus, progesterone can apparently exert biphasic effects on the induction of receptivity in female mice. In this regard, the mouse appears similar to the guinea pig and rat.