Enhancement by progesterone of lysergic acid diethylamide inhibition of the copulatory response in the female rat.

Copulatory behavior in the ovariectomized rat, the lordosis response (L.R.) was induced by either estrogen alone or estrogen followed by progesterone. L.R. has been shown to be inhibited dose-dependently by lysergic acid diethylamide (LSD). The effects of various hormone treatments on the LSD-induced inhibition were tested in the present study. Progesterone but not estrogen was found to significantly enhance the LSD effect in a dose-dependent manner. In contrast, the effect of LSD on spontaneous behaviors in an exploratory situation was not influenced by progesterone treatment. This phenomenon of increased L.R. inhibitor effect by LSD was probably not due to a steroid-induced change in LSD metabolism. The data show instead that progesterone specifically influences monoaminergic mechanisms, which are related to the action of LSD. This has important implications for the possibility that progesterone induces the L.R. by acting on monoaminergic mechanisms.