抄録
Roles of ovarian inhibin and steroids in the regulation of basal secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) were examined during pseudopregnancy in the rat. Bilateral or unilateral ovariectomy performed on either day 5 or 10 of pseudopregnancy (day 0; the day after copulation with a vasectomized male) produced a significant increase in plasma FSH concentrations within 6 h. During the subsequent 18 h, plasma FSH concentrations in unilaterally ovariectomized rats declined to a baseline level, and the gonadotropin concentrations in bilaterally ovariectomized rats remained significantly elevated above the value measured in sham-operated (control) animals. Plasma LH concentrations on either day 5 or 10 were not significantly altered by bilateral or unilateral ovariectomy. Plasma inhibin concentrations on both days 5 and 10 declined to an undetectable level within 6 h after bilateral ovariectomy. In unilateral ovariectomized rats, compared to control animals, a significant decrease in plasma inhibin concentrations was evident at 6 and 12 h, but not at 24 h, after the operation on both days 5 and 10. On day 5, administration of charcoal-treated porcine follicular fluid (an inhibin preparation) eliminated the increase in plasma FSH concentrations produced by bilateral ovariectomy within 24 h without affecting plasma LH concentrations. Plasma FSH and LH concentrations in rats bilaterally ovariectomized on day 5 were not significantly altered by administration of estradiol or progesterone alone, whereas both gonadotropin concentrations in these animals were slightly but significantly suppressed as late as 24 h after combined administration of estradiol and progesterone. In addition, in intact pseudopregnant rats, administration of antiserum against inhibin resulted in a marked increase in plasma FSH concentrations accompanied by a small but significant increase in plasma LH on day 5. These results collectively suggest that ovarian inhibin is a major regulator of FSH secretion during pseudopregnancy in the rat.
