Administration of gonadotropin-releasing hormone to pregnant rats inhibits postpartum sexual behavior.

Dunlap KD, Sridaran R.

Department of Physiology, Morehouse School of Medicine, Atlanta, GA 30310.

Administration of gonadotropin-releasing hormone (GnRH) can both facilitate sexual behavior in estrogen-primed, ovariectomized rats and induce numerous antifertility effects in pregnant rats. The present study was undertaken to determine the effect of GnRH treatment on 1) sexual behavior of rats during late pregnancy and at postpartum and 2) plasma levels of dihydrotestosterone (DHT) and progesterone (P), two hormones implicated in the regulation of sexual behavior during pregnancy. Rats were given either 4 micrograms or 12 micrograms GnRH or no treatment on day 18 of pregnancy. On days 18 (4 hr posttreatment) and 19 of pregnancy, the day of parturition and the day following parturition, each rat was tested for lordosis response to male mounts and subsequently bled from the jugular vein for determination of plasma DHT and P levels by radioimmunoassay. Both doses of GnRH significantly inhibited lordosis at postpartum estrus and failed to induce lordosis on days 18 and 19 of pregnancy and the day following parturition. DHT was suppressed on day 19 and at postpartum; P was elevated on the day following parturition. Our data demonstrate that as little as 4 micrograms GnRH can induce postpartum "behavioral antifertility" effects without apparent detriment to the pregnancy.