Biphasic stimulatory effects of XXXX on gonadotropin surges induced by continuous administration of gonadotropin-releasing hormone in @entity1 .

@entity172 @entity1 @entity1420 @entity53 @entity1176
The present experiments were performed to study the effects of preovulatory levels of @entity172 on @entity1176 -induced gonadotropin release. Twelve female volunteers in various phases of the menstrual cycle received @entity53 infusion for 66 h at a constant rate of 500 micrograms/24 h which is grossly equivalent to its production rate during the preovulatory follicular phase. In 8 of the @entity1 , @entity1176 was administered concomitantly from 6 h after the initiation of @entity53 infusion. The administered doses of @entity1176 were 2.5 and 5 micrograms/h. Blood samples obtained throughout the infusion were analysed for LH, FSH, @entity53 and @entity1420 . The sole administration of @entity53 failed to induce the positive feedback effect on gonadotropin release within the experimental period in the early follicular phase (days 3-7) in 4 @entity1 . In 5 @entity1 treated during the follicular phase, remarkable LH releases were induced after a lag period by the infusion of both @entity1176 and @entity53 . The induced LH surge formed a prolonged biphasic pattern. Although a similar pattern of FSH was observed in some cases, its response was minimal compared with that of LH. In 3 @entity1 during the luteal phase, however, a combined administration of @entity53 and @entity1176 induced only a short term release of LH which was terminated in only 12 h. The present data indicate that 1) Preovulatory levels of @entity172 affect the late part of the LH surge which is induced by constant administration of low doses of @entity1176 resulting in a prolonged biphasic release of LH, and 2) These effects of both hormones are not manifest in the presence of high levels of @entity1420 . These results indicate the possibility of a role of @entity1176 and @entity172 in the mechanism of the prolonged elevation of a gonadotropin surge at mid-cycle.
