Testosterone

Testosterone is a male sex hormone produced by the testes that encourages the development of male sexual characteristics, stimulates the activity of the male secondary sex characteristics, and prevents changes in them following castration.

How It Works

Testosterone is the most potent of the naturally occurring androgens. The androgens cause the development of male sex characteristics, such as a deep voice and a beard. They also strengthen muscle tone and bone mass.

High levels of testosterone appear to promote good health in men, for example, lowering the risks of high blood pressure and heart attack. High testosterone levels also correlate with risky behavior, however, including increased aggressiveness and smoking, which may cancel out these health benefits.

History

Testosterone was once thought to do no more than activate and oversee the male reproductive systems. Research on the female sex hormone estrogen led to further understanding about the influence of testosterone on the brain. In the 1970s, researchers found evidence that mature female rats had brain cells with receiving areas, known as receptors, which were specifically constructed to process estrogen. This suggested that a woman's estrogen could help the brain perform certain duties. Since that time, many studies indicate that the hormone can aid memory in women as well as protect their brains from developing ailments such as the memory impairing disorder, Alzheimer's disease (AD).

Taking this lead, researchers recently examined testosterone and found that it also provides men with some brain advantages.

For example, new studies show that supplements of testosterone can aid certain types of memory in men suffering from AD. These man have been shown to have low levels of testosterone. This hormone may improve working memory, which allows a person to manipulate information over brief periods of time in order to make a response. Verbal memory, which helps a person recall lists of words, and spatial memory, which helps a person navigate a route, also benefit.

How It Works

Testosterone may prevent AD by preventing the brain destruction that marks this disease. Studies of rat brain cells found that the hormone limits the production of beta-amyloid peptides. These sticky protein fragments, thought to be a prime contributor to AD, build up into small, round deposits and clog the brains of people with the disease.

The hormone also may prevent AD by directly decreasing brain cell death. In studies, researchers manipulated human brain cells, sending them on a course to die (a term called apoptosis). Adding doses of testosterone, however, limited the cell death.

While together the results show a new positive side to testosterone, scientists say they need to conduct more research before they would encourage people to take testosterone supplements to prevent AD.

Side Effects

With its benefits, the powerful hormone also may create some negative effects. For example, some believe that it increase the risk of developing prostate cancer in certain recipients. Additional studies on large groups of people will help researchers evaluate whether the benefits of testosterone supplementation outweigh the risks.

Uses

Testosterone may be given to treat medical conditions, including female (but not male) breast cancer, hypogonadism (low gonadal function) in the male, cryptorchidism (nondescent of the testis into the scrotum), and menorrhagia (irregular periods).

Interesting Facts

• In males, the testes produce most of the circulating testosterone. The hormone LH from the pituitary gland stimulates the Leydig cells in the testicles to produce testosterone.

• In females, the ovaries produce most of the testosterone. The adrenal cortex produces another male hormone, called DHEAS, which is related to testosterone.

• A testosterone test measures the amount of the male hormone in the blood.

How the Test is Performed

• Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

• The health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from the arm. Once the blood has been collected, the needle is removed, and the puncture site is covered with a piece of cotton to stop any bleeding.

• In infants or young children, a sharp tool called a lancet may be used to puncture the skin and draw bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

Testosterone levels are used to assess:

• Early or late puberty in boys
• Impotence and infertility in men
• Excess hair growth, male body characteristics (virilization), and irregular menstrual periods in women

Normal Results

Male: 300 -1,000 ng/dL Female: 20 - 80 ng/dL Note: ng/dL = nanograms per deciliter

Normal value ranges may vary slightly among different laboratories.

What Abnormal Results Mean

High levels of testosterone:

• Androgen resistance
• Congenital adrenal hyperplasia
• Ovarian cancer
• Polycystic ovary disease
• Precocious puberty
• Testicular cancer

Low levels of testosterone:

• Chronic illness
• Delayed puberty
• Hypopituitarism
• Prolactinoma
• Testicular failure