Endocrinology & Disorders

Male Reproductive Endocrinology

The hypothalamus produces gonadotropin-releasing hormone (GnRH), which is released in a pulsatile fashion every 60 to 120 minutes. Its target organ, the anterior pituitary gland, responds to each pulse of GnRH by producing a corresponding pulse of luteinizing hormone (LH) and, to a lesser degree, follicle-stimulating hormone (FSH). If the GnRH pulses do not occur with the proper amplitude, frequency, and diurnal variation, hypogonadism may result (idiopathic hypogonadotropic hypogonadism). Continuous (as opposed to pulsatile) stimulation by GnRH agonists (eg, as a treatment for advanced prostate cancer) actually suppresses pituitary release of LH and FSH and thus testosterone production. Testosterone is synthesized from cholesterol through several intermediate compounds, including dehydroepiandrosterone (DHEA) and androstenedione. Circulating testosterone is mostly protein bound, about 40% avidly bound to sex hormone–binding globulin (SHBG) and 58% loosely bound to albumin.