Cellular localization of ovarian histamine, its cyclic variations, and histaminergic effects on ovulation in the rat ovary perfused in vitro

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Abstract
Summary. Mast cells, visualized with toluidine blue staining and the Falck-Hillarp fluorescence technique, were mainly located around large blood vessels in the hilus region of the ovary in adult rats and in immature rats treated with PMSG. Histamine concentration in the rat ovary was significantly reduced after the LH surge in PMSGtreated animals, corresponding to a reduced number of ovarian mast cells. No marked change in the number of mast cells and histamine concentration was found in adult rats during the oestrous cycle. Histamine as well as the H1-agonist, 2-methylhistamine, and the H2-agonist, 4-methylhistamine, induced ovulations in the isolated perfused rat ovary. Ovulation rates were significantly lower than those evoked by LH. The histamine liberator, Compound 48/80, induced ovulations which were blocked by the combined effect of the H1- and H2-histamine receptor antagonists, cimetidine and pyrilamine. The anti-degranulating agent, disodium cromoglycate, did not block ovulations induced by Compound 48/80. The results show that the level of ovarian histamine, which is primarily stored in mast cells, can be influenced by PMSG treatment, and that the amine is able to induce ovulations in gonadotrophin-primed rats by an effect mediated by both H1 and H2 receptors. Keywords: histamine; ovary; in vitro; ovulation