BETA-ENDORPHIN INHIBITS PROSTAGLANDIN SYNTHESIS IN RAT OVARIES AND BLOCKS INDUCED OVULATION

The aim of the present study was to explore the action of exogenous be ta-endorphin on the number of oocytes ovulated and on prostaglandin (P G) production in ovaries isolated from pregnant mare's serum gonadotro pin/human chorionic gonadotropin(PMSG/hCG)-primed immature rats. An in trabursal injection of the opioid (0.084 mu g) was given 4 hours after hCG and the number of oocytes within the oviducts on the following mo rning was reduced (P < 0.05). The same effect was also attained with a n intraperitoneal (IP) injection (0.5 mu g). The time course of PG syn thesis was quantified in ovaries of rats treated with an IP injection. Eight hours after hCG, prostaglandin content increased (P < 0.01) and remained high until 12 hours after hCG (P < 0.001). This increase was inhibited by the in vivo treatment with beta-endorphin. On isolated o varies, beta-endorphin (10(-8) MJ had a clear inhibitory action on pro staglandin production. beta-Endorphin's effect on prostaglandin synthe sis in the ovaries is of importance in the ovulatory process. The poss ible physiological role of beta-endorphin merits further investigation .