Testosterone Production Sites in Males
In males, testosterone is primarily produced by Leydig cells in the testes, with a small additional contribution from the adrenal cortex. 1, 2
Primary Production Site: Testicular Leydig Cells
The testes account for approximately 95% of circulating testosterone in males, with Leydig cells being the specialized steroidogenic cells responsible for this synthesis 2, 3, 4
Testicular testosterone production begins as early as 7-8 weeks of gestation in the developing male fetus, with Leydig cells differentiating between days 16-18 after conception in animal models 1
By 14-18 weeks of gestation, Leydig cells occupy approximately half the volume of fetal testes, producing testosterone levels in the adult male range that are essential for male genital differentiation 1
Hormonal Regulation of Testicular Production
Luteinizing hormone (LH) from the pituitary gland is the central regulatory molecule controlling testosterone synthesis in Leydig cells 5, 6
LH stimulates the enzymatic conversion of cholesterol to testosterone through a series of steroidogenic reactions within Leydig cells 2, 5
The final enzymatic step in the canonical testosterone production pathway is controlled by hydroxysteroid-dehydrogenase-17-beta-3 (HSD17B3), though alternative pathways involving HSD17B12 can maintain basal testosterone production 4
Secondary Production Site: Adrenal Cortex
In adult males, the adrenal cortex produces androgen precursors that contribute minimally to total testosterone levels, with the vast majority coming from testicular sources 2
This contrasts with females, where both adrenal cortex and ovaries produce precursors that are converted to testosterone peripherally, resulting in testosterone concentrations approximately 15-fold lower than in males 2
Clinical Relevance
Primary hypogonadism results from testicular dysfunction (Leydig cell failure), while secondary hypogonadism stems from impairment of the hypothalamic-pituitary-gonadal axis that regulates LH secretion 1
Understanding these anatomical sites is essential when evaluating testosterone deficiency, as the location of dysfunction determines whether hypogonadism is classified as primary (hypergonadotropic) or secondary (hypogonadotropic) 1