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Sunday, May 20, 2012



We are often bombarded with the question and the statement of low virility. In this series of blogs about male hormonal health, I have been discussing libido and erectile dysfunction. In some cases it may be due to low testosterone. But, in order to understand what is low, we first need to understand what testosterone is, what its main function is and then by doing so, we can understand what happens when it goes low.

What is Testosterone?

Testosterone is a steroid hormone. Hormones are the main communicators of the body and generate effects throughout the systems. Testosterone is found in mammals, reptiles, birds and other vertebrates. In humans, testosterone is primarily secreted by the Leydig cells in male testicles, and at lower levels it is also secreted by the female ovary and the adrenal glands. Secretions of hormones usually follow an internal clock and are highest early in the morning. On average, an adult male produces about 7-8 times more testosterone than an adult female, but females are more sensitive to the hormone.

Testosterone is the primary and the most well-known of many hormones that belong to the androgen group. Androgens are also called androgenic steroid hormones or testoids. It is the generic term given to any natural or synthetic compound that stimulates or controls the development and maintenance of male characteristics. It classically binds to specific androgen receptors everywhere in the body. Androgens control the development and activity of the male sex organs and development of male secondary sex characteristics. Androgens are the original anabolic steroids and the precursor of all estrogens, the female sex hormones.

How is Testosterone Measured?

There are many ways to measure testosterone; the most common one is via a blood test. When measuring testosterone and the different hormones that are related to its proper function, doctors usually measure the brain hormones that drive the production. The brain hormones associated with sexual differentiation are Follicular Stimulating Hormone (FSH) and Luteinizing Hormone (LH). Testosterone is also carried in the blood by Sex Hormone Binding Hormone (SHBH) and therefore there is a total pool of the carried ones, and the free ones: Total Testosterone and Free Testosterone.

In males, the normal range of Testosterone in blood is between 270 to 1,070 nanograms, with an ideal average level of 679 nanograms. (Pennsylvania State University Study)

Testosterone can also be measured in the saliva. These values are usually measure the bioavailable levels of steroid hormones active in the tissue.

What are the effects of Androgens and Testosterone?

In general, androgens promote protein synthesis and growth of those tissues with androgen receptors. Testosterone effects are mostly dependent on the levels and duration of circulating free testosterone in the body. The effects on the body are both virilizing and anabolic. This means that in men, testosterone will further the maturation of the sex organs and promote male characteristics. In women, high levels of testosterone can cause for the presence of more male-like characteristics. The anabolic effects of androgens are the ones that cause growth of muscle mass and strength, increased bone density and strength, and stimulation of linear growth and bone maturation.

 Effects of Testosterone in the body (in chronological order):

1. Between 4 and 6 weeks of the gestation testosterone starts being produced and the effects of the hormone cause genital virilization and the formation of the penis, prostate and seminal vesicles.

2. During the 2nd trimester of pregnancy increasing androgen and testosterone levels have been associated with gender identity. Some studies state that during this period, intrauterine exposure to high androgens may be a predictor to feminine or masculine behaviors. This is still controversial.

3. In the first weeks of life for male infants testosterone levels rise. The levels remain in a pubertal range for a few months, but usually reach the barely detectable levels of childhood by 4–6 months of age. The reason for this is not clearly understood. . It has been speculated that "brain masculinization" is occurring since no significant changes have been identified in other parts of the body.

4. During puberty one of the first signs of the effect of androgens are the following:

  •  Adult type body odor
  • Increased oiliness of skin and hair
  • Acne
  • Face changes where there is loss of subcutaneous fat and development of masculine facial  features such as growth of jaw, brow, chin, nose, and remodeling of facial bone contours
  • The appearance of pubic hair is first, then comes axillary hair and last is chest and facial hair
  • Growth spurt
  • Increased muscle strength and mass
  • Shoulders become broader and rib cage expands
  • Voice changes and deepens
  • Development and growth of the Adam's apple
  • Accelerated bone maturation
  • Enlargement of the scrotum, penis and testicles
  • Increased libido and frequency of erection
  • Growth of spermatogenic tissue in testicles, male fertility
5. Adult: Aa a male adult, the male features are maintained, yet there continues to be constant effects of testosterone and androgens in the body.
  • Testosterone is necessary for normal sperm development. It activates genes in Sertoli cells, which promote differentiation of sperm. Throughout adulthood, androgens, testosterone and FSH cooperatively act on Sertoli cells in the testes to support sperm production
  • Maintains muscle tone and promotes muscle enlargement under stimulation with exercise and weights
  • Regulates bleeding and clotting via effects of thromboxane A2 receptors
  • In the brain, androgens can influence human behavior, and change the structure of the brain, and induce a sense of wellbeing, motivation, exhilaration and euphoria
  • Increases libido
  • Increased aggression
  • Regulates cognitive and physical energy
  • Inhibition of fat deposition and the ability for the fat cell to store lipids
What about other Androgens?

Other androgenic steroid hormones are also very important in the body. They are produced mainly in the adrenal cortex and support the main effects of testosterone. These hormones can also be found in the form of supplements. I will discuss this in further detail in my next blogs about low testosterone and the different treatments available.

Other androgens include:

Dehydroepiandrosterone (DHEA): a steroid hormone produced in the adrenal cortex from cholesterol. It is the primary precursor of natural estrogens. DHEA is also called dehydroisoandrosterone or dehydroandrosterone.

Androstenedione: an androgenic steroid produced by the testes, adrenal cortex, and ovaries. While androstenediones are converted metabolically to testosterone and other androgens, they are also the parent structure of estrone. Use of androstenedione as an athletic or body building supplement has been banned by the International Olympic Committee as well as other sporting organizations.

Androstenediol: the steroid metabolite that is thought to act as the main regulator of gonadotropin secretion.

Androsterone: a chemical by-product created during the breakdown of androgens, or derived from progesterone, that also exerts minor masculinizing effects, but with one-seventh the intensity of testosterone. It is found in approximately equal amounts in the plasma and urine of both males and females.

Dihydrotestosterone (DHT): a metabolite of testosterone, and a more potent androgen than testosterone in that it binds more strongly to androgen receptors. It is produced in the adrenal cortex.

Now that I have explained the effects of testosterone in men, in my next blog I will present to you a questionnaire about testosterone and androgen deficiency. This will further interest you in the next blog explaining what is low testosterone and what a person can do about this situation. Stay tuned…. And have a great weekend.

Margarita Ochoa-Maya, MD

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