Cells of the testis lying between the testicular tubules in which sperm are formed (hence their other name, interstitial cells), and responsible for the production of the male sex hormone testosterone under the influence of luteinising hormone.

Any hormone that switches on the function of the gonads. There are two main families of gonadotropins: (a) the gonadotropin that stimulates the growth of the follicle, or follicle stimulating hormone (FSH); and (b) those that cause ovulation from the mature follicle and stimulate the corpus luteum that results to develop and to produce progesterone, namely luteinising hormone (LH) and human chorionic gonadotropin (hCG). FSH will cause growing follicles to produce the estrogen estradiol, provided that a small amount of LH (or hCG) is present. FSH and LH are produced in the pituitary gland, whereas hCG comes from the placenta in pregnancy. In men, FSH stimulates the Sertoli cells of the testicular tubules, and hence drives spermatogenesis; LH and hCG stimulate the Leydig cells to produce testosterone.

(LH) The hormone, or gonadotropin, produced by the pituitary gland to cause, in women, ovulation of a mature follicle in the ovary, resulting in formation of the corpus luteum; in men, stimulates the production of testosterone by the Leydig cells of the testis. Suppressed by GnRH-agonists and GnRH-antagonists, so that (for ovulation induction) an injection of human chorionic gonadotropin (hCG), which acts the same way, has a predictable time course of action. A small amount of LH is essential for normal function of the tertiary follicle and the corpus luteum. Recombinant LH is under development by Serono as Luveris, but its clinical role in place of hCG is not yet established.

The main constituent of the testis, lined by Sertoli cells and containing the developing sperm cells. Lying between the tubules are the interstitial or Leydig cells.