Testosterone is secreted by

Testosterone * C19 steroid with a hydroxyl group in the 17th position * Testosterone is synthesized from cholesterol in the leydig cells (by 17 alpha hydroxylase) * Testosterone is also formed androstenedione secreted by adrenal coex(by 11 and 21 hydroxylases) * Secretion of testosterone is under the control of LH * Rate of secretion of testosterone - 4-9mg/dl in adult men * Plasma testosterone level (free and bound) - 300- 1000ng/dL in adult men * 98% of testosterone in plasma is bound to protein (65% -bound to beta globulin / gonadal steroid binding globulin / sex steroid binding globulin) and (33% bound to albumin) * Testosterone binds to an intracellular receptor * The receptor/steroid complex then binds to DNA in the nucleus * This facilitates the transcription of many genes * In addition, testosterone is also conveed to Dihydrotestosterone by 5 alpha reductase in some target cells. DHT binds to the same intracellular receptor as testosterone Ref:- Ganong's Review of Medical Physiology 25th ed; pg num:- 422