Progesterone and 3 alpha-androstanediol conjugated to bovine serum albumin affects estrous behavior when applied to the MBH and POA.

Ovariectomized rats with cannula over the medial basal hypothalamus (MBH) received implants of 3 alpha-diol conjugated to bovine serum albumin (BSA; 3 alpha-diol:BSA), free 3 alpha-diol diluted with BSA (3 alpha-diol&BSA), progesterone (P) conjugated to BSA (P:BSA), free P diluted with BSA (P&BSA), or BSA alone. 3 alpha-diol:BSA or 3 alpha-diol&BSA facilitated receptivity within 90 min. Other estradiol-treated rats received steroid implants in the preoptic area (POA); those receiving P:BSA or P&BSA showed significant elevations in lordosis in 5 min. When systemic P was given, 3 alpha-diol:BSA and 3 alpha-diol&BSA applied to the MBH or POA inhibited receptivity. When 3 alpha-diol was given systemically, 3 alpha-diol:BSA implants to the MBH and POA produced facilitatory effects. These data suggest 3 alpha-diol can act at the membrane and that these effects are influenced by circulating steroids; yet membrane-mediated actions do not account for all of P-facilitated sexual behavior in the MBH and POA.