ANDROGENS, LIBIDO, AND SEXUAL ACTIVITY
Although androgen hormones are often referred to as "male hormones",
they are secreted by the adrenal glands in addition to the testes. As
a result, androgens are normal hormones for both men and women, although
the relative concentrations may vary. Androgens are synthesized from
both the ovaries and adrenal glands and estrogens are synthesized by
both the testes and adrenal glands. Some females actually produce more
testosterone than some males (Rogers, 2001).
In males, the production of testosterone increases in the male fetus early in the third month of development through birth. It mediates effects on the male genetalia and hypothalamus during this time. About 2 months after birth there is another surge in testosterone production which last several months although its significance is not understood. The final surge in testosterone production occurs during puberty where it contributes to growth, development of the primary sex organs and secondary sexual characteristics, and influences sexuality, personality, violence, and other cognitive aspects (Ramirez, 2003).
The largest study done on female sexual dysfunction (FSD) concluded that it affects 43% of women in the United States. This study based on the U.S. National Health and Social Life Survey of 1992 also found that among women with FSD, 51% had low libido. This makes it the most prevalent female disorder (22% of all women), followed by arousal problem (33%) and pain disorders (16%) (Mahmoud, 2006). Androgens are used to treat low libido in women in general Androgens are used to treat the loss of libido in postmenopausal women (Genazzani, 2002; Mahmoud, 2006).
In order for the gonads to secrete steroid hormones after puberty, they need to stimulated by hormones from the pituitary gland (FSH and LH) which are in turn produced in response to a hypothalamic hormone GnRH. A number of mutations can interfere with this mechanism and cause hypogonadotrophic hypogonadism. Mutations may affect GnRH, the GnRH receptor, or the migration of the GnRH producing cells from their embryonic origin in the nose to the hypothalamus (Kallman's syndrome which also involves the inability to smell). Since the onset of puberty relies on the signal leptin and its receptor (among others), mutations in these genes delay the onset of puberty and cause hypogonadism (MacColl, 2002; Bulow, 2002). Male libido and interest in women is absent in men with Kallman syndrome which is caused by a failure of GnRH secreting cells to migrate from the nose to the brain (which then eliminates the signal to the pituitary which in turn eliminates the signal to the testes to make testosterone) (Pfaff, 1997).
The major androgen synthesized in the ovaries is androstendione and that of the adrenal glands is DHEA (dehydroepiandrosterone). These can be converted to testosterone by the liver and skin (Eriksson from Steiner, 2000).
Salivary testosterone levels are associated with levels
of sexual activity in adolescent males (Pfaus, 1999). Testosterone levels
are higher the morning after intercourse in men who mated with unfamiliar
partners or multiple partners (Van Anders, 2007). Testosterone levels
and the likelihood of masturbation are inversely associated with relationship
commitment (Van Anders, 2007).
Androgens also increase irritability in men and women. High
levels of androgens may be associated with the irritability of some parts
of the menstrual cycle in females (Steiner, 2003). In men, chemical castration
is linked to increased risk of depression and anxiety. Ending chemical
castration coincides with improved performance in memory. Decreased testosterone
levels are linked to depression and testosterone supplementation improves
some types of cognitive ability (Almeida, 2004).
Adrenal and ovarian levels of androgen decline in women as they age. Oral contraceptives can lower androgen levels by decreasing LH levels and by increasing the amount of sex hormone binding globulins (SHBG) which can bind androgens and make them less available. Glucocorticoids reduce ACTH secretion and thus androgen secretion (Mahmoud, 2006).
Estrogen therapy can also improve physical problems in sexual activity (such as inadequate lubrication, vaginal congestion, or muscle contraction) and libido (Mahmoud, 2006)