Role of histamine in the increased secretion of prolactin induced by ether in adult male rats.

The purpose of the present work was to determine the possible role of the histamine receptors located in the rostral zone of the hypothalamus in the control of the prolactin surge induced by ether stress. Cannulae were implanted into the preoptic anterior hypothalamic area or the third ventricle of several groups of adult male rats under ether anaesthesia. On the following day the rats wee cannulated in the jugular vein so that they could be bled frequently. Twenty-four hours later saline, metiamide (an antagonist of H2 histamine) or pyrilamine (an antagonist of H1 histamine) were injected into the brain. Fifteen minutes after the injection all rats were subjected to an ether stress. Blood samples were taken at regular times after the stress and prolactin levels determined by radioimmunoassay. A prolactin surge was observed in rats injected with saline which extended up to 15-30 min after the stress. When the histamine antagonists were administered directly in the rostral hypothalamus both pyrilamine and metiamide inhibited the prolactin surge. When the histamine antagonists were administered into the third ventricle only metiamide was able to block the prolactin response completely. The present results suggest that histamine receptors in the rostral hypothalamus of the rat are involved in the control of prolactin secretion induced by stress.