The hypothalamus communicates with the pituitary by neural pathways and by a portal vascular system that delivers regulatory hormones from the brain to the pituitary (Fig. 11.4). The preoptic and medial basal regions of the hypothalamus (particularly the arcuate nucleus) control gonadotrophin secretion. Peptidergic neurones in these regions secrete the decapeptide gonadotrophin-releasing hormone (GnRH), also known as luteinising hormone-releasing hormone (LHRH). Neurones from other regions of the brain terminate in this area and influence GnRH synthesis and release via catecholaminergic, dopaminergic, and b-endorphin-related mechanisms. GnRH is widely distributed in the central nervous system and in other tissues, but a physiological role for GnRH outside the pituitary is not established.
