What Is the Relationship Between Testosterone & the Pituitary?

The pituitary gland is small anatomical structure within the brain, located immediately below the hypothalamus, which governs its activity. Hormones produced by the pituitary regulate functions of key organs, including the testes.

Hypothalamic-Pituitary-Gonadal (HPG) Axis

• As a closely interrelated endocrine unit, the hypothalamus, pituitary and the gonads control development of primary and secondary sex characteristics, spermatogenesis and reproduction.

Physiology

• The hypothalamus secretes gonadotropin-releasing hormone (GnRH), which, in turn, stimulates the pituitary to release the follicle-stimulating hormone (FSH) and luteinizing hormone (LH). In males, LH prompts the testes to produce testosterone, while FSH stimulates manufacture of sperm. GnRH and LH discharge is suppressed via negative feedback loop by testosterone.

Testosterone Levels

• During the course of puberty, GnRH production surges, leading to a dramatic rise in testosterone levels and development of secondary sexual characteristics. Testosterone levels reach the highest point shortly after puberty and remain at these concentrations until roughly the fourth decade. A very gradual decline thereafter is accompanied by a slight rise in LH and FSH.

HPG Axis Dysfunction

• Disturbance along any segment of the HPG axis can precipitate in hypogonadism, or testosterone deficiency, in males. Primary hypogonadism occurs when the testes are unable to produce sufficient testosterone. Secondary hypogonadism involves dysfunction of the pituitary or hypothalamus.

Hypogonadism Etiology

• Hypogonadism can be attributed to a wide range of causes, including central nervous system disorders, tumors, alcoholism, radiation therapy, chemotherapy, genetic abnormalities, systemic diseases, exposure to toxic chemicals and synthetic estrogens, obesity and heavy marijuana use, among others.