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Leydig cell
Leydig cells, known also as interstitial cells of Leydig, are found adjacent to the seminiferous tubules in the testicle.
Leydig cells produce testosterone in the presence of luteinizing hormone (LH).
Leydig cells appear as polyhedral in shape, and have a large prominent eccentrically placed nucleus, an eosinophilic cytoplasm and numerous lipid-filled vesicles.
The nucleus contains one to three prominent nucleoli.
Leydig cell acidic cytoplasm contains membrane-bound lipid droplets and large amounts of smooth endoplasmic reticulum, scattered patches of rough endoplasmic reticulum, and mitochondria are also prominent within the cytoplasm.
Lipofuscin pigment and rod-shaped crystal-like structures 3 to 20 micrometres in diameter known as Reinke crystals are also found.
Reinke crystals have no known function, are found in less than half of all Leydig cell tumors.
Leydig cells differentiate in the post-natal testis and are quiescent until puberty.
Fetal- type Leydig cells from the 8th to the 20th week of gestation produce enough testosterone for masculinisation of a male fetus.
Leydig cells release androgens, 19-carbon steroids.
Leydig cells secrete testosterone, androstenedione and dehydroepiandrosterone (DHEA), when stimulated by the luteinizing hormone (LH).
Luteinizing hormone is released from the anterior pituitary in response to gonadotrophin releasing hormone which is released by the hypothalamus.
LH binds to its receptor G-protein coupled receptor and consequently increases the production of cAMP.
cAMP, stimulates cholesterol translocation from intracellular sources to the mitochondria, and is
followed by pregnenolone formation from the translocated cholesterol in the inner mitochondrial membrane, eventually leading to testosterone synthesis and secretion by Leydig cells.
Prolactin increases the response of Leydig cells to LH by increasing the number of LH receptors expressed on Leydig cells.
Leydig cells tumors are usually benign in nature, but may be hormonally active, secreting testosterone.