Effects of passive immunization against oestradiol-17β and inhibin on the secretion of gonadotrophin in the cyclic golden hamster (Mesocricetus auratus)

Abstract

To investigate the physiological importance of oestradiol-17b and inhibin in the regulation of gonadotrophin secretion in the cyclic golden hamster, females were passively immunized against two hormones. When 200 µL antiserum against oestradiol-17β (oestradiol-AS) was given on Day 3 (Day 1 = day of ovulation), the preovulatory gonadotrophin surge was completely blocked for 24 h and the length of the oestrous cycle was also prolonged for one day. In the group given 200µL oestradiol-AS on Day 3, basal levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) increased slightly and superovulation (19·6 ± 0·8, mean ± s.e.m.) occurred. When 200 µL antiserum against inhibin (inhibin-AS) was given at 1100 hours on Day 3, a dramatic increase in plasma FSH and a slight increase in LH were noted, resulting in superovulation (38·2 ± 2·6) on the expected Day 1. The present study indicates clearly that inhibin plays a major role in regulating the specific ovulation rate in the hamster through the control of FSH secretion. Present results also indicate that oestradiol-17β suppresses basal LH secretion. Oestradiol-17β may act as an indicator of the follicular maturation, and the high plasma concentration of oestradiol-17β noted from Day 3 to Day 4 may play an important role in determining the timing of initiation of the preovulatory gonadotrophin surge.