Proposed explanations for the suppression of gonadal function in hyperprolactinaemia include suppression of gonadotrophin secretion; inhibition of positive oestrogen feedback on luteinising hormone (LH) secretion in women; an increase in adrenal androgen secretion; and blockade of the effects of gonadotrophins at the gonadal level (Fig. 4.18). It is probable that an important mechanism is prolactin feedback at the hypothalamus, which alters secretion of gonadotrophin-releasing hormone (GnRH), thus causing LH and follicle-stimulating hormone (FSH) secretion to become inappropriately low, relative to gonadal steroid levels. Abnormalities in LH pulsatility also occur. Prolactin may interfere with LH and FSH action at the gonad, blocking progesterone synthesis, and may stimulate adrenal androgen secretion.
