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The Science of Sex: Testosterone

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Testosterone — The Female Sex Hormone


Testosterone. The word has come to symbolize the excesses of male sexuality. It’s the steroid that turns choirboys into rapists, that fuels the engine of aggressive, competitive, promiscuous, risk-taking sex — male sex. And yet, as it turns out, testosterone is a vital female sex hormone, too.

    

How can that be? The very name testosterone, after all, reminds us of its origin in the testes, glands that only men possess. Yet women’s bodies, specifically their ovaries and adrenal glands, also manufacture testosterone, along with related hormones that are collectively known as androgens (“male-makers”). Recent research suggests that androgens are at least partially responsible for women’s sex drive, just as they are for men’s.

    

The reason it has taken scientists so long to recognize testosterone’s role in women has to do with a major difference between the sexuality of women and that of female laboratory animals such as rats. In female rats, as in most other mammals, the sex drive varies greatly around the estrous cycle. Females will only engage in sex near the time of ovulation, when they are capable of becoming pregnant. These variations in sexual behavior are controlled by variations in the level of the “female” sex hormones, estrogen and progesterone.

    

Women (and the females of some higher primate species) are sexually active around the entire menstrual cycle, as well as during pregnancy and after menopause, so the estrogen/progesterone system is evidently not the key player in regulating women’s sex drive. Many researchers concluded that women’s sex drive is hard-wired into their brains and is independent of circulating sex hormones.

    

Clues that hormones might be important after all came from observations on women whose ovaries and/or adrenal glands had been surgically removed. The removal of the adrenal glands in particular is commonly followed by a rapid decline in sex drive, and this decline can be reversed by administration of testosterone or other androgens.

    

Recently a group of researchers at the University of Utrecht, Holland, led by psychologist Adriaan Tuiten, set out to test whether testosterone influences the sexual feelings of healthy women. The study was sponsored by a manufacturer of sex hormones. Half of the women were given testosterone and half a dummy drug; neither the subjects nor the doctors knew which subjects received which drug. At various intervals after drug administration, the women viewed videotapes showing men and women engaged in sex. During the viewing, the researchers monitored the walls of the women’s vaginas with a photoelectric device. This device detects color changes as the tissue becomes engorged with blood — a physiological indicator of arousal. In addition, the women subjectively assessed their own state of sexual arousal at intervals throughout the experiment. Later, the women who had received the dummy drug got the real thing, and vice versa.

    

About four hours after drug administration, women who received the testosterone responded to the videotapes with a significantly higher degree of arousal (as measured by the photoelectric device) than did the women who received the dummy pill. In addition, the increase in physiological arousal correlated to the women’s subjective sense of increased sexual excitement.

    

The Dutch researchers concluded that testosterone does contribute to sexual arousal in women. By itself, the study does not tell us whether the hormone acts directly on the brain, or whether the effect is only at the level of the genitalia. After all, women might become mentally aroused as an indirect consequence of the sensations coming from their engorged vaginas. Other studies suggest that vaginal engorgement by itself does not promote mental arousal, however, so testosterone probably acts directly on women’s brains, just as it does in men.

    

It’s worth noting that, in adults, testosterone influences the level of sexual arousal, but not the kind of stimulus that a person finds arousing. In years past, testosterone was given to some gay men in a misguided effort to make them sexually interested in women. In fact, they simply became even more interested in having sex with men. Similarly, there is no reason to think that a heterosexual woman who takes testosterone or other androgens will develop lesbian tendencies.

    

When administered during fetal life, on the other hand, testosterone may influence a person’s ultimate sexual orientation, as I’ve discussed in a previous column,

“Fingers and fetuses”. It’s thought that, in fetal life, testosterone and other androgens cause the brain to develop in a male-typical direction, but that in adulthood, they merely stimulate the activity of whatever sexual circuitry has already been set up.