Involvement of H1 Histamine Receptor in Basal and Estrogen-Stimulated Luteinizing Hormone-Releasing Hormone Secretion in Rats in vitro

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Abstract
For determination of the roles of histamine and its receptors, H1 and H2, in the control of basal and estrogen-induced LH-RH secretion, the mediobasal hypothalamus (MBH) and/or pituitary was excised from normally cycling female rats and perifused in an in vitro sequential double chamber perifusion system. Administration of 10–7M histamine caused significant release (90–170% increase, p < 0.05) of LH from the pituitary in sequence with the MBH, whereas 10–7M histamine had no effect on LH release from the pituitary perifused alone; administration of 10–5M 2-methylhistamine, an H1 agonist, induced significant release (50–120% increase, p < 0.05) of LH-RH from the MBH, and addition of 10–5M mepyramine, and H1 antagonist, abolished this LH-RH release. The LH concentrations in the efflux were not affected by the administration of the H2 agonist 4-methylhistamine. Estradiol caused significant release of LH-RH from the MBH and LH from the pituitary in sequence with the MBH. The estradiol-induced release of LH-RH and LH were completely abolished by perifusion with medium containing 10–5M mepyramine. The H2 receptor antagonist ranitidine did not affect estradiol-induced LH release. Histamine did not change the LH release induced by 20 ng LH-RH. These findings suggest that histamine induces release of hypothalamic LH-RH, and that histamine H1 receptors in the hypothalamus are involved in the basal and estradiol-induced LH-RH release.