Acute Effects of Estradiol and Follicle-Stimulating Hormone on Specific Binding of Human [125I]Iodo-Follicle-Stimulating Hormone to Rat Ovarian Granulosa Cellsin vivoandin vitro*

Abstract

Twenty-four-day-old hypophysectomized and intact immature female rats were used to determine the time-dependent effects of estradiol on FSH stimulation of FSH receptor in granulosa cells. In hypophysectomized rats, a single 2 μg injection of human (h) FSH (LER-1577) given alone, concomitantly with, or 6 h after 1.5 mg estradiol caused a 50% increase in the available FSH receptor content in granulosa cells by 24 h. The same dose of hFSH given 12 or 24 h after estradiol caused a 300% increase in available FSH receptor by 24 h. To establish the accuracy of these in vitro FSH-binding assays, it was imperative to determine if the hFSH administered in vivo occupied binding sites and thereby masked increases in total available FSH receptor occurring within the first 24 h. Therefore, 20 × 106 cpm of 125I-labeled hFSH, equivalent to 250 ng hFSH LER-1577, was administered sc to estradiolpiimed hypophysectomized rats 1 h after an injection of saline or 2 μg hFSH. The amount of labeled hormone bound in vivo to 30,000...