Characterization of histamine receptors mediating contraction and relaxation of the ovarian follicle wall.

Histamine is known to be present in ovarian tissue and may play a role in the ovulation process. The effect of histamine on the follicular smooth musculature was investigated using strips from the protruding part of mature bovine follicles, mounted in vitro for registration of isometric motor activity. Histamine contracted the preparation in a concentration-dependent manner. The response was inhibited competitively by the specific H1 receptor antagonist pyrilamine while the adrenergic alpha-receptor antagonist phentolamine had no clear-cut effect. A Schild plot revealed a pA2 value of 8.81, corresponding to a mean KB value (dissociation constant for receptor-antagonist complex) of (7.5 +/- 3.2) X 10(-9) M. After potassium depolarization and blockade of the contractile H1-receptors with pyrilamine, histamine induced a concentration-dependent relaxation of the follicle wall preparation. This response could be inhibited by the H2-receptor antagonist cimetidine (which also potentiated the contractile effect in the absence of pyrilamine). The pA2 value for the cimetidine-induced inhibition was 6.25, and KB was found to be (6.5 +/- 3.0) X 10(-7) M. The beta-receptor antagonist propranolol was effective only in very high concentrations. It is suggested that a possible role for histamine during follicle rupture is mediated via specific receptors in the follicular smooth musculature.