Effect of Anti-Androgen and 5α-Reductase Inhibitor on Hormone-Induced Sexual Behavior During Pregnancy in the Rat

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Abstract
The ability of estradiol benzoate (EB) or EB plus progesterone (P) to induce estrous behavior in the rat is substantially decreased during pregnancy, an effect not solely attributable to high titers of circulating P. The possible contribution of 5α-dihydrotestosterone (DHT) to the inhibition of lordotic responsiveness during pregnancy was studied. As few as three daily injections of DHT-propionate (DHTP) to ovariectomized rats treated concurrently with EB caused a significant reduction in sexual receptivity. Furthermore, daily treatment of ovariectomized rats with an androgen receptor-blocker (Flutamide, 5 mg/day) in combination with EB and DHTP facilitated the display of lordosis. The 5α-reductase inhibitor, 4-androstan-3-one, 17β carboxylic acid (17βC, 3 mg/day), also resulted in increased sexual receptivity in ovariectomized rats treated concurrently with testosterone propionate (TP). However, pregnant females given 7-9 daily injections of Flutamide or 17βC in these dosages were no more receptive than control animals in tests conducted on postcoital Day 16 following treatment with EB plus P. These data suggest that factors other than circulating DHT are primarily responsible for the suppression of behavioral responsivenss to ovarian hormones which occurs in the rat during pregnancy.