Abstract
The role of estradiol in regulating the secretion of LH and FSH from diestrus to proestrus of rats was examined by neutralizing estradiol using antiserum against estradiol (estradiol-AS). An IV injection of varying doses of estradiol-AS at 1100 h on diestrus caused a significant rise in plasma LH (maximally 318.2 ± 27.3% vs control) and non-significant rise in plasma FSH (maximally 144.0 ± 22.0% vs control) at 6 hours after the injection. Administration of the antiserum prolonged the estrous cycle and the day of ovulation by 1 day. The prolongation was caused by a 1-day delay of the LH surge. A small but significant increase in the number of tubal oocytes shed was noted in the estradiol-AS treated group (16.3 ± 0.8, n=12) compared with controls (14.5 ± 0.4, n=15). These results indicated that estradiol suppresses tonic secretion of LH and that the steroid may also be concerned with the regulation of FSH. They also confirmed that the rise in plasma estradiol from diestrous morning is necessary for triggering the LH surge on the following afternoon. Further, administration of estradiol-AS on diestrus resulted in a significant increase in the number of oocytes shed, probably due to the increase in tonic secretion of LH and FSH between diestrus to proestrus.
