ABSTRACT
The hypothalamic–pituitary–gonadal axis is central to the control of reproduction. In primates, neurons scattered widely throughout the hypothalamus synthesize a decapeptide, gonadotrophin releasing hormone from a large precursor. Gonadotrophin secretion in the male is subject to negative feedback control by both of the secretions from the testis. Testosterone acts at the hypothalamus and the anterior pituitary, both express androgen receptors. The end of reproductive life, the menopause, is characterized by ovarian failure; the hypothalamus and pituitary continue to function. Prolactin (PRL) secretion is regulated by the hypothalamus, by dopaminergic neurons which are inhibitory, and by a number of peptides which activate secretion, a pattern similar to control of growth hormone (GH) secretion. Like GH, both exercise and stress stimulate prolactin release. PRL concentrations are high during pregnancy and lactation. The fall in cyclic adenosine monophosphate concentration reduces transcription of the prolactin gene.
