The adrenal glands lie atop the kidneys and produce several different types of hormones. The inner core, or medulla, of the adrenal glands produces "stress hormones" like epinephrine--adrenaline--while the outer layer or cortex produces androgens, the family of "male" steroids that includes testosterone. The adrenal glands are a source of testosterone for both men and women.
Cholesterol forms the building block of steroid hormones. With the help of the protein steroidogenic acute regulator, or StAR, cholesterol shuttles to the mitochondria, where enzymes convert it to the steroid hormone pregnenolone. Through one pathway of chemical reactions catalyzed by various enzymes, adrenal cells can convert pregnenolone to hydroxyprogesterone, and then to adrenal androgens like testosterone.
The outer portion or cortex of the adrenal gland produces different steroid hormones in defined zones or layers. Each zone contains a distinct set of starting products and enzymes that operate in specific steps of steroid production, and their availability limits the types of steroids that each zone can produce. The deepest layer of the adrenal cortex, called the zona reticularis, is the only part of the adrenal gland that makes adrenal androgens.
The zona reticularis of the adrenal gland itself produces a small amount of testosterone while predominantly secreting "weak" androgens such as dehydroepiandrosterone, or DHEA, and DHEA sulfate, or DHEA-S, into the blood. Compared to testosterone, DHEA and DHEA-S bind less efficiently to the androgen receptors that convert hormone signals into cellular results. However, some target tissues for DHEA and DHEA-S convert those weak androgens to testosterone, amplifying the strength of the cellular response. When scientists mention "adrenal testosterone," they really mean testosterone resulting from the target tissue conversion of the DHEA and DHEA-S produced by the adrenal glands. In this roundabout way, the adrenal glands are an important source of testosterone.
Effects in Men
In men, the contribution of testosterone derived from the adrenal glands pales to insignificance in comparison to the normal output of testosterone from the testicles. Either over-secretion or under-secretion of adrenal androgens usually does not have any noticeable consequences in men.
Effects in Women
The ovaries make testosterone, but most of it is immediately converted to estrogen, so in women the adrenal glands are the primary source for testosterone. The most noticeable effect of adrenal-derived testosterone in women is the appearance of pubic hair and underarm hair. When women have too much adrenal-derived testosterone, they suffer from masculinization or virilization, encompassing a suite of traits such as irregular menstrual periods, shrinkage of the breasts and clitoris, acne, low voice, excess thick hair on the face and other "male typical" parts of the body, and typical male muscle development, says the Merck Manual.
After menopause, when the ovaries sharply curtail estrogen production, conversion of adrenal-derived testosterone to estrogen becomes an important source of "female" hormones.