15th April 2024

Basic physiology

Activation of hypothalamic GnRH neurons initiates the reproductive hormone axis, this is initiated in response to energy status and peripheral sex hormone levels leading to the onset of puberty.  The onset of puberty leads to pulsatile secretion of GnRH into the hypothalamic-pituitary portal blood supply, GnRH binds to receptors on the cell membrane of pituitary gonadotrophic cells in the anterior pituitary gland.

Stimulation of pituitary gonadotrophic cells leads to the release of follicle stimulating hormone (FSH) and luteinising hormone (LH) in a pulsatile manner.  These travel via the systemic circulation to the testes binding to FSH and LH receptors (G-protein coupled receptor) located on the plasma membrane of Sertoli and Leydig cells, respectively, and the activation of secondary c-AMP protein kinase signalling pathways.

Activation of Leydig cells via activation of the LH receptor leads to the production of testosterone, whereas activation of FSH receptors on Sertoli cells leads to the production of proteins such as inhibin A &B, CYP19A1 and other proteins assisting spermatogenesis. The release of testosterone from the Leydig cells of the testes inhibits the release of GnRH and FSH/LH from the hypothalamus and pituitary gland.