Lordosis facilitation in estrogen primed rats by intrabrain injection of pregnanes.

Progesterone (P) and nine of its natural metabolites were bilaterally injected (5 micrograms in 0.5 microliter oil) into either the ventromedial hypothalamus (VMH) or the medial preoptic area (MPOA) of estrogen primed rats to assess their relative potencies for stimulating lordosis. P, 5 alpha-pregnanedione and 5 beta, 3 beta-pregnanolone elicited lordosis when injected at either VMH or MPOA. By contrast, 5 alpha, 3 beta-pregnanolone as well as 20 alpha-OH and 20 beta-OH-pregnenone were much more effective in stimulating lordosis when implanted in the MPOA. Finally, 5 beta-pregnanedione and 5 beta,3 alpha-pregnanolone did not stimulate lordosis at neither VMH nor MPOA. The observation that lordosis was induced in estrogen primed rats both by pregnanes that bind to the P receptor (i.e., P; 5 alpha-pregnanedione; 20 alpha- and 20 beta-OH-pregnenone) and by pregnanes that do not (i.e., 5 alpha, 3 beta-; 5 beta,3 beta- and 5 alpha,3 alpha-pregnanolone) indicates that diverse cellular mechanisms are involved in the facilitation of lordosis by pregnanes.