An autoradiographic study of the binding of 125 I-labeled follicle-stimulating hormone, human chorionic gonadotropin and prolactin to the hamster ovary throughout the estrous cycle.

Abstract

Specific tissue binding sites for follicle-stimulating hormone (FSH), human chorionic gonadotropin (hCG) and prolactin (Prl) were identified in the cyclic hamster ovary to provide a better understanding of the role of gonadotropins in the regulation of ovarian function. At 0800 h on Days 1–4 and at 1200 h, 1600 h and 2000 h on Day 4 (Day 1=day of ovulation and Day 4=proestrus with the LH surge occurring by 1600 h), ovaries were obtained from hamsters, frozen and serially sectioned. Selected sections were incubated with 125I-labeled FSH, hCG or FrI and processed for autoradiography. FSH binding to granulosa and oocytes of healthy follicles increased progressively with follicular size but was always notably reduced or absent in atretic follicles. Corpora lutea (CL) exhibited substantial FSH binding on Day 1; however binding was much lower on Day 2 and not detected on Day 3. hCG bound moderately to interstitial cells (IC) and thecae of all follicles. hCG binding was not detected in granulosa of preantral follicles but appeared in basal mural granulosa of growing antral follicles on Day 2 and then increased progressively to include all of the mural granulosa and became maximal at 1200 h on Day 4. This binding was slightly reduced at 1600 h and 2000 h on Day 4. hCG binding to granulosa of atretic antral follicles was always notably less than to healthy antral follicles and binding was never detected in the cumulus or oocyte of any follicle. hCG binding to CL was moderate on Day 1, sharply increased and maximal on Day 2, and then markedly reduced on Days 3 and 4. Prl binding to CL, IC and follicles followed the same pattern as for hCG on Days 1–3. On Day 4 at 0800 h, thecae of preantral follicles and IC exhibited moderate Prl binding and CL had very light binding. In addition, thecae and mural granulosa of healthy antral follicles had high Prl binding whereas binding was notably lower in atretic antral follicles. At 1600 h and 2000 h on Day 4, overall Prl binding to ovarian tissues was markedly decreased. Several new findings in the present study appear to be biologically significant: 1) the sharp reduction in Prl binding at the time of and at least 4 h after the LH and FSH surges suggests that either or both of these hormones may regulate Prl binding, and/or the loss of Fri binding may play a role in ovulation and/or luteinization: 2) FSH binding to CL suggests FSH has a role in CL function: 3) and FSH binding to the cumulus and oocyte suggests that FSH may play a role in oocyte growth and maturation.