Leydig cell
Endocrinocytus interstitialis
Also known as: interstitial cell of Leydig, interstitial endocrine cell
Steroid-secreting cells lying in clusters between the seminiferous tubules that produce testosterone in response to LH.
Overview
Leydig cells are large polygonal eosinophilic cells clustered near capillaries in the interstitial tissue. They have the classic ultrastructure of steroid-producing cells — abundant smooth endoplasmic reticulum, mitochondria with tubular cristae, and lipid droplets of cholesterol esters — and often contain rod-shaped Reinke crystals of unknown function.
LH binds the LH/hCG receptor (Gs/cAMP) and stimulates cholesterol transport into mitochondria (StAR) and its conversion to testosterone through pregnenolone, progesterone/17-hydroxyprogesterone and androstenedione. Testosterone diffuses into the seminiferous tubules (where Sertoli-cell androgen-binding protein holds it at very high concentration) and into the blood.
There are two populations: fetal Leydig cells, active from ≈8 weeks under placental hCG (masculinisation of the fetus), and adult Leydig cells, which appear at puberty.
- Location
Interstitial connective tissue between the seminiferous tubules of the testis.
Anatomy
- Histology
Eosinophilic, lipid-rich cytoplasm; round nucleus; Reinke crystals; abundant SER and tubular mitochondrial cristae on electron microscopy.
Function
- Synthesise and secrete testosterone (≈6–7 mg/day in adult men).
- Secrete INSL3, which drives the transabdominal phase of testicular descent.
- Regulation
LH (stimulates); testosterone and estradiol inhibit LH (negative feedback). hCG also activates the receptor (used to stimulate testosterone in hypogonadotropic hypogonadism).
Clinical significance
Leydig-cell tumours
Usually benign; secrete androgens (precocious pseudopuberty in boys) or estrogens (gynaecomastia in men); may contain Reinke crystals.
Relative resistance to injury
Leydig cells tolerate chemotherapy and radiotherapy better than germ cells, so men treated for cancer often keep normal testosterone but become azoospermic (hence sperm banking before treatment).
Compiled from standard anatomy and physiology references — see the Reproductive System sources. For education only; not medical advice.