Leydig cell

Leydig cells are the testosterone factories of the testis. They sit in the spaces between the sperm-making tubules, like workers stationed in the corridors rather than inside the production rooms, and their single great task is to manufacture and release the male sex hormone.

Leydig cells respond to luteinizing hormone (LH) from the pituitary. When LH binds its receptor on the cell surface, it triggers the conversion of cholesterol into testosterone through a chain of steroidogenic enzymes. The testosterone they secrete enters the blood to masculinize the body and also reaches very high local concentrations inside the neighboring seminiferous tubules, where it is essential for sperm production.

Because Leydig cells are the LH-driven hormone source, problems with them produce primary hypogonadism: low testosterone with high LH, since the brain pushes harder when feedback is missing. This contrasts with secondary (central) hypogonadism, where the pituitary fails to make enough LH in the first place. Distinguishing the two by measuring LH alongside testosterone is a routine first step in evaluating low testosterone.