NALTREXONE ENHANCES OVULATION AND PROSTAGLANDIN SYNTHESIS IN THE RAT OVARY

We explored the action of beta-endorphin (beta E) and naltrexone (Nal) on the number of oocytes and on prostaglandins (PGE and PGF(2 alpha)) , production by the ovaries from PMSG/hCG-primed immature and cycling rats. Superovulated rats were injected with beta-endorphin (0.5 mu g) intraperitoneally 4 hours after hCG. The number of ova ovulated was in hibited and this effect was blocked with naltrexone injected into the ovarian bursa (0.1 mu g) 30 minutes before beta-endorphin. Furthermore beta-endorphin (10(-8) M) decreased prostaglandins production by ovar ies isolated 4 hours after hCG. Intraperitoneal injection of beta-endo rphin (0.5 mu g) at 17:00 hr on proestrus decreased (-23%) the number of ova within oviducts on the day after (estrus). Naltrexone injected intraperitoneally (5 mu g) at 16:30 hr on proestrus increased the numb er of ova (+23%). On the other hand, beta-endorphin increased the numb er of oocytes obtained by puncture of antral follicles (+37%) and nalt rexone decreased the number of oocytes (-33%). Prostaglandins content in the ovary of adult rats at 23:00 hr, approximately 4 hr before the onset of ovulation, was diminished when the rats received beta-endorph in at proestrus. Moreover, when the rats were injected with naltrexone , ovarian production of prostaglandins was increased. Our results furt her support the hypothesis that beta-endorphin affects ovulation at th e level of the ovary in the rat and that endogenous opioids may be mod ulating this physiological process.