[Role of histaminergic H1 and H2 receptors in prolactin release in humans].

Histamine is considered as a neurotransmitter, since it is present in hypothalamus and pituitary gland. It has been reported to stimulate prolactin (PRL) release in rats and humans; it seems to be involved in the control of LH release in rats. But cimetidine, an H2 antagonist also induces PRL release in humans. To investigate the relationship between the PRL secretion and possible histaminergic pathways, the response of PRL and LH was studied for 180 minutes in 10 normal subjects (5 men, 5 women) after H1 antagonist (diphenhydramine 50 mg iv), H2 antagonist (cimetidine 300 mg iv) and placebo. Diphenhydramine and placebo injection resulted in a decrease of PRL from 0800 until 11.00 hours, suggesting a spontaneous diurnal variation. Cimetidine induced a short but significant rise of PRL before a similar diurnal secretory pattern. LH levels were unaffected by H1 and H2 antagonists. These data suggest that PRL and LH secretion in humans is unresponsive to H1 histaminergic pathways. The specific action of cimetidine remains to be defined.