The role of aromatization in the restoration of male rat reproductive behavior.

This study assessed the role of aromatization in the expression of male reproductive behavior by testing the effects of the aromatase inhibitor, fadrozole, on the restoration of male sexual behavior and partner preference in testosterone-treated gonadectomized rats. We measured nuclear estrogen receptor occupation to determine whether fadrozole blocked brain aromatase. In addition, nuclear androgen receptor assays were used to verify that fadrozole does not block androgen receptors. Mini-osmotic pumps fitted to brain infusion cannulas were used to deliver fadrozole (20 micrograms/day) into the right lateral ventricle. The majority of animals receiving fadrozole treatment with two, 10 mm testosterone filled Silastic capsules (T/F group) failed to display any sexual behavior 7 and 13 days following implant surgery. In contrast, animals receiving fadrozole treatment which were implanted with two, 10 mm testosterone capsules and one, 5 mm 1% estradiol capsule (T/F/E group) copulated normally, indicating that fadrozole's inhibition of male sex behavior was specifically due to blocking aromatase activity. Moreover, the animals which received only one, 5 mm 1% estradiol capsule (E group) also failed to exhibit male sexual behavior. Partner preference for either a sexually receptive female or a non-receptive female was measured in a three chambered apparatus for an index of sexual motivation. Repeated measures contrasts on the group x test interaction indicated that the T/F group was not significantly different from the T group. In addition, the E group did not show a preference for the receptive females and was significantly different from the T group. Fadrozole treatment resulted in a 59% decrease in brain nuclear estrogen receptor occupation relative to the T group. Fadrozole had no significant effect on brain nuclear androgen receptor occupation. Our results lend support to the hypothesis that both androgen receptor activation and aromatization are necessary for the restoration of male sexual behavior in rats. However, we found that estradiol is neither necessary nor sufficient for the restoration of partner preference.