If androgens are of importance for sexual behaviors in women, then we should expect no or minor variation during the menstrual cycle. As might be remembered, some studies have reported a slight increase in blood androgen concentrations around ovulation, but that increase is very small compared to what is seen with estrogens. The data reviewed a couple of paragraphs above show that variations in sexual functions during the menstrual cycle are small and unreliable, perhaps even absent. This coincides nicely with the androgen hypothesis. Ovariectomy has no effect on sexual behavior in women, as we have seen. We know that this intervention reduces androgen concentrations with as little as 25% (Judd et al., 1974), or at most with 50% (Laughlin et al., 2000). The concentration of estrogens is, not surprisingly, reduced far more. The modest reduction in androgen concentrations does not seem to affect sexual functions. This lack of effect is, nevertheless, easier to account for than the same lack of effect of the large reduction in estrogens. In men, it is known that the physiological concentration of androgens is above that needed for maintenance of sexual behaviors (Bhasin et al., 2001). In women, it has been suggested that androgen insufficiency might be suspected as a cause for impaired sexual behaviors when the blood concentration is below 25% of the mean concentration for the age (Rivera-Woll et al., 2004). If this is true, then the reduction in androgen concentrations following ovariectomy should not be large enough to affect sexual behaviors. This reasoning is supported by data mentioned above.
In order to observe a reduction in sexual behavior in women caused by androgen deficiency, a large decline in blood concentration appears to be necessary. There are indeed some women whose blood androgen concentration is extremely low. This is the case in women who have been subjected to adrenalectomy in addition to ovariectomy. Not only are the main sources of testosterone suppressed, but also most of the testosterone precursors that normally are transformed into testosterone in peripheral tissues are removed. The adrenal cortex is the main site of synthesis of these precursors, and extirpation of the adrenal will eliminate production of them. In adrenalectomized, ovariectomized women, sexual behaviors are much reduced (Waxenberg et al., 1959) and they can be restored by treatment with androgens. Severe androgen deficiency following treatment with cytotoxic agents in ovariectomized women has also been reported to markedly decrease sexual responsiveness (Kaplan and Owett, 1993). These observations render strong support to the notion that androgens indeed are crucial for sexual behaviors in women. The deleterious effect of adrenalectomy + ovariectomy cannot be explained by a deteriorated health after these operations, because the women concerned reported improved health following surgery. The reason for removing the adrenals in addition to the ovaries was to eliminate all sources of estrogens in breast cancer patients, and getting rid of the tumor as well as the prospect of avoiding relapse had, not unexpectedly, beneficial health effects.
Since plasma androgen concentrations are not reduced during menopause, we should expect pre- and menopausal women to have the same level of sexual behaviors, provided that other factors that might affect sexual activity are excluded. In view of the lack of effect of menopause on the genital response to sexual incentives, we must conclude that this prediction is confirmed. The marginal importance of phase of the menstrual cycle, ovariectomy and menopause all suggest that androgens rather than estrogens are crucial for sexual behaviors in women. The large inhibitory effects of adrenalectomy combined with ovariectomy, and its reversal by androgen replacement, gives further support to the notion that androgens are important. I conclude by suggesting that women are more similar to other primates than to rodents with regard to the endocrine control of sexual behaviors, nothing else.
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