Leydig cells

Leydig cells, also known as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle. They can secrete testosterone and are often closely related to nerves. Leydig cells have round vesicular nuclei and a granular eosinophilic cytoplasm.

Nomenclature
Leydig cells are named after the German anatomist Franz Leydig, who discovered them in 1850.

Functions
Leydig cells release a class of hormones called androgens (19-carbon steroids). They secrete testosterone, androstenedione and dehydroepiandrosterone (DHEA), when stimulated by the pituitary hormone luteinizing hormone (LH). LH increases cholesterol desmolase activity (an enzyme associated with the conversion of cholesterol to pregnenolone), leading to testosterone synthesis secretion by Leydig cells.

Follicle-stimulating hormone (FSH) increases the response of Leydig cells to LH by increasing the number of LH receptors expressed on Leydig cells.

Ultrastructure
Leydig cells are polygonal, eosinophilic cells with a round vesicular nucleus and contain lipid droplets. They contain abundant smooth endoplasmic reticulum, which accounts for their eosinophilia. Frequently, lipofuscin pigment and rod-shaped crystal-like structures (Reinke's crystals) are found.

Development
Leydig cells form during the 16th and 20th week of gestation and are quiescent until puberty.