The Effects of Testosterone on the Testis

According to an article published by "The Independent" in 2010, men experience physiological changes akin to female menopause. Male hypogonadism occurs when a man's testicles cannot produce adequate levels of testosterone. According to Northwestern Memorial Hospital urologist, Dr. Robert Brannigan, more than five million American men experience hypogonadism and more than 95 percent of these cases are not diagnosed. Brannigan estimates that testosterone levels start dropping after age 35 and continue dropping approximately one percent each year. Athletic performance boosting with testosterone is controversial. Testosterone affects testicular conditions, because the testicles produce most testosterone in men.

Size and Shape

Testosterone affects the size and shape of the testicles. The testicles naturally produce testosterone, which contributes to the size and shape of the testicles. According to Drugs.com, testosterone enanthate, testosterone cypionate and testosterone gel can have side effects that include changes in the size and shape of the testes. MayoClinic.com lists "shrunken testicles" among common side effects of anabolic-androgenic steroids, which are synthetic derivatives of testosterone. Clinicians may attempt to offset testicular shrinkage with human chorionic gonadotropin, or HCG. HCG helps prevent testicle shrinkage and infertility. HCG may also boost adrenal functioning, libido and overall energy.

Testosterone Production

Exogenous testosterone, or testosterone that does not come from a man's Leydig cells, affects the production of natural testosterone in the testicles. The testicles stop producing their own testosterone by introducing exogenous testosterone to the body via testosterone injections, oral medication, skin patches, creams or gels. The testicles shrink because exogenous testosterone shuts down their normal testosterone production system. The body detects testosterone from an external source and stops producing its own. Since testicular testosterone contributes to sperm production, this condition can reduce a man's sperm count. This condition can lead to testosterone dependence. Clinicians may offset reduced testosterone production in the testicles with human chorionic gonadotropin. HCG stimulates Leydig cells in the testicles to produce testosterone.

Estrogen Production

Testosterone affects estrogen production in the testicles. According to a Society for the Study of Reproduction study published in 2010 in the journal "Biology of Reproduction," adding testosterone to testicular rat cells produced estrogen in vitro. The study found that pre-pubertal rat testicles produced more estrogen after a testosterone injection, and most of the estrogen remains in the testicles for about three hours. The male human body converts excess exogenous testosterone into estrogen inside the testicles. Estrogen is a female hormone that can have effects like fatigue, impotence, water retention, depression and brain fog in men. Prolonged high levels of estrogen can lead to. Clinicians may offset estrogen production in the testicles with aromatase inhibitor medications. Aromatase is the enzyme responsible for converting testosterone into estrogen. Aromatase inhibitors block aromatase enzymatic activity.