Effect of histamine and histamine blockers on the ovulatory process in the vitro perfused rabbit ovary.

An increase in the content of histamine in the ovary following luteinizing hormone (LH) release and the inhibition of ovulation in the rabbit by antihistamines suggest that histamine may be involved in the ovulatory process. The effects of various doses of histamine and antihistamines on ovulation were investigated using the in vitro perfused rabbit ovary system. Histamine (100 ng/ml) added to the perfusate at hourly intervals induced ovulation, although at a rate below that observed following human chorionic gonadotropin (hCG) administration. Cimetidine (10 micrograms/ml), an H2 blocker, inhibited histamine-induced ovulation, while the H1 blocker, chlorpheniramine (66.7 micrograms/ml), failed to do so. Neither cimetidine nor chlorpheniramine was able to block ovulation following hCG (50 IU). In all experimental groups in which histamine was used to induce ovulation, both extruded ova and follicular oocytes remained in an immature stage and displayed little evidence of degeneration. In contrast, a high percentage of ova exposed to hCG were mature. Ovarian edema was increased in ovaries in which ovulation occurred, regardless of treatment. A linear correlation was noted between ovulatory efficiency and degree of ovarian edema. Histamine may be an intermediary in the mechanism of follicular rupture, but does not support ovum maturation. However, the inability of H1 and H2 antagonists to block hCG-induced ovulation raises questions regarding the role of histamine in the physiologic process of ovulation.