Theoretical review. Progesterone: inhibition of rodent sexual behavior.

The inhibitory effects of progesterone (P) can be observed in many vertebrates of either sex. In female rodents, P man act to terminate the period of receptivity and to prevent proestrus reinduction of receptivity at times when plasma P is minimal (immediately postestrus) or maximal (during the luteal phase). Inhibition is probably accomplished via an interaction with estrogen although P does have profound general anesthetic properties. Inhibition of receptive behavior has been induced by P implanted in the rodent midbrain, but implants in other regions of the central nervous system were ineffective. This correlates with the observation that rodent midbrain concentrates P more that other brain regions. Modes of progesterone-estrogen interaction are discussed.