Testosterone is a sex hormone primarily found in males and functions to trigger the development of both primary and secondary sexual characteristics that occur during puberty. It is also found in females to a lesser amount and serves several important roles in the female physiological system.
The effects of testosterone typically begin to manifest in the first few weeks of intra-uterine life. At about the seventh week of gestation within the uterus, the presence of the Y chromosome leads to the development of the primordial testes. Once developed, the primordial testes begin to produce testosterone and Mullerian Inhibiting Factor, which are essential for the differentiation of the fetus into a male rather than a female. The release of testosterone in the uterus leads to the development of the male primary physical characteristics such as epididymis, vas deferens, seminal vesicles, penis, prostate gland, and the descent of the testicles into the scrotum in the last months of fetal life.
During puberty in males, there is a significant surge in testosterone produced and released within the body. This increase in testosterone production is under the control of the hypothalamic-pituitary-gonadal axis. The hypothalamus releases Gonadotropin-releasing hormone (GnRH) in the brain, which then travels down to the anterior pituitary gland by means of the hypothalamic-hypophyseal portal system. In the anterior pituitary gland, GnRH causes the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH). The released LH acts on the Leydig cells within the testes to increase the amount of testosterone produced. Once released, testosterone facilitates the development of secondary sexual characteristics in males, such as enlarged genitalia, increased libido, sperm production, deepening of the voice, and growth of male hair patterns on the body.
In addition to the development of male secondary sexual characteristics, testosterone also serves other essential functions within the body. Some of these functions include:
- Skeletal muscle: Testosterone has a hypertrophic and hyperplastic effect on the muscle fibers within the skeletal muscular system. There is a significant increase in muscle growth during puberty due to the hypertrophic effects of testosterone. In men experiencing muscle loss due to aging, testosterone administration has been shown to aid in reversing this condition.
- Bone: Testosterone has a significant impact on the development and maintenance of bone growth. It is converted to estradiol by means of the enzyme aromatase; estradiol minimizes the breakdown of bone by inhibiting the resorption of bone by osteoclasts. Additionally, testosterone is converted into dihydrotestosterone (DHT) by the enzyme 5-alpha reductase; DHT stimulates bone osteoblasts and the laying down of bone.
- Blood: Testosterone stimulates the production of red blood cells in males. This is one of the reasons that males generally tend to have higher red blood cell levels compared to females. The process by which testosterone stimulates red blood cell production is not yet fully understood and is undergoing research.
- Brain: Some studies have shown that testosterone levels in the body have an impact on the ability of males to reason and perform other higher mental functions. These studies indicate that most men suffering from hypogonadism due to low testosterone may experience some degree of memory impairment as well as impaired verbal and visual performance.
- Mood: Though also poorly understood, testosterone levels in the body have been shown to have an effect on the mood and behaviors in males. There is an association between hypogonadism in men and depressive moods. Research performed revealed an improvement in moods in men with hypogonadism after treatment with testosterone supplements.
Testosterone enanthate is an injectable testosterone supplement that is usually administered to treat low testosterone and other symptoms of hypogonadism in males. It is a slow-release oil-based ester that can be administered either intramuscularly or subcutaneously, depending on the health care provider’s preference or the individual receiving the injection. It was first used clinically as a treatment of low testosterone in 1937, and its use by men has since then significantly increased in popularity.