EFFECTS OF PASSIVE-IMMUNIZATION AGAINST ESTRADIOL-17-BETA AND INHIBINON THE SECRETION OF GONADOTROPIN IN THE CYCLIC GOLDEN-HAMSTER (MESOCRICETUS-AURATUS)

To investigate the physiological importance of oestradiol-17 beta and inhibin in the regulation of gonadotrophin secretion in the cyclic gol den hamster, females were passively immunized against two hormones. Wh en 200 mu L antiserum against oestradiol-17 beta (oestradiol-AS) was g iven on Day 3 (Day I = cay of ovulation), the preovulatory gonadotroph in surge was completely blocked for 24 h and the length of the oestrou s cycle was also prolonged for one day. In the group given 200 mu L oe stradiol-AS on Day 3, basal levels of follicle-stimulating hormone (FS H) and luteinizing hormone (LH) increased slightly and superovulation (19.6+/-0.8, mean+/-s.e.m.) occurred. When 200 mu L antiserum against inhibin (inhibin-AS) was given at 1100 hours on Day 3, a dramatic incr ease in plasma FSH and a slight increase in LH were noted, resulting i n superovulation (38.2+/-2.6) on the expected Day 1. The present study indicates clearly that inhibin plays a major role in regulating the s pecific ovulation rate in the hamster through the control of FSH secre tion. Present results also indicate that oestradiol-17 beta suppresses basal LH secretion. Oestradiol-17 beta may act as an indicator of the follicular maturation, and the high plasma concentration of oestradio l-17 beta noted from Day 3 to Day 4 may play an important role in dete rmining the timing of initiation of the preovulatory gonadotrophin sur ge.