Regulation of the Hypothalamic-Pituitary-Testicular Axis: Pathophysiology of Hypogonadism.

Male hypogonadism is a clinical syndrome characterized by the diminished functional activity of the testis resulting in low levels of testosterone and/or spermatozoa. Defects at one or more levels of the hypothalamic-pituitary-testicular (HPT) axis can result in either primary or secondary hypogonadism. The changes that occur in the HPT axis from fetal to adult life are fundamental to understanding the pathophysiology of hypogonadism. In this article, we summarize the maturation and neuroendocrine regulation of the HPT axis and discuss the major congenital and acquired causes of male hypogonadism both at the (1) hypothalamic-pituitary (secondary hypogonadism) and (2) testicular (primary hypogonadism) levels.