Hypothalamic gonadotrophin releasing hormone (GnRH) exerts its effect on gonadotrophin synthesis and release via plasma membrane-bound receptors. The exocytosis of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) is activated by the binding of GnRH or its agonists to receptors in pituitary cells, which initiates a number of post-receptor events within the gonadotroph cell. Various potential second messengers have been claimed to mediate the stimulatory action of GnRH including calcium, inositol phosphates, protein kinase C, arachidonic acid metabolites and cyclic nucleotides. It appears that more than one of these pathways is required to fully mimic the GnRH effect.