Duration of Estrogen Exposure Prior to Follicle-Stimulating Hormone Stimulation is Critical to Granulosa Cell Growth and Differentiation in Rats1

Abstract

Estrogens have been reported to exert both stimulatory and inhibitory effects on granulosa cell function. Previous studies from our laboratory showed that 12 h after administration of diethylstilbestrol (DES; a synthetic estrogen), FSH-stimulated granulosa cell proliferation and aromatase activity were increased; however, 48 h after DES, FSH stimulation of both parameters was inhibited. In other experiments, exposure of rats to DES for a period of 26 h blocked ovulation in response to eCG and hCG administration, whereas the same treatment regimen without DES caused ovulation in all treated rats. Thus, DES may in some cases actually interfere with maturation and development of ovulatory follicles. The present study was designed 1) to confirm that the duration of estrogen pre-exposure determines the way granulosa cells respond to FSH and 2) to investigate the underlying mechanisms involved. While DES was used in preliminary experiments, the majority of the studies were conducted with estradiol, a natural estrogen, in order to conform as closely as possible to the normal physiology. In the experimental protocol, immature female rats received injections of DES or implants of estradiol pellets 12 h (short exposure) or 36 h (long exposure) before 36 h of FSH treatment. Rats were killed, ovaries removed, and granulosa cells collected at the end of the FSH treatment period. The results demonstrate that exposure to either of these estrogens for 12 h allowed the subsequent FSH stimulation to produce high cellular proliferation, high aromatase enzyme activity, and large amounts of FSH receptor and aromatase mRNA. Estrogen exposure for 36 h, however, resulted in significantly decreased FSH stimulation of all these parameters. These findings confirm that short exposure to estrogen enhances the response of granulosa cells to FSH while longer exposure makes granulosa cells refractory to FSH. This differential sensitivity of granulosa cells to estrogen exposure could help explain how dominant follicles survive to ovulate while others are lost to atresia during ovarian cycles.

Relationship between follicle size at insemination and pregnancy success

“…Estradiol has the following actions within granulosa cells: (i) increased cellular proliferation (21)(22)(23), (ii) formation of gap junctions (24,25), (iii) increased stimulatory action of folliclestimulating hormone on aromatase activity (26)(27)(28), (iv) enhanced stimulation of progestin synthesis after gonadotropin stimulation (29,30), and (v) enhanced acquisition of luteinizing hormone receptors (31)(32)(33). Furthermore, the ability of luteinized human granulosa cells to secrete progesterone was increased when cells were collected from follicles having increased follicular fluid concentrations of estradiol compared with granulosa cells collected from follicles with lower concentrations of estradiol (20), and secretion of progesterone was delayed in ewes given an aromatase inhibitor before induced ovulation (34).…”

Gonadotropin-releasing hormone antagonists increase follicular fluid insulin-like growth factor-I and vascular endothelial growth factor during ovarian stimulation cycles

“…E 2 plays an important role in oocyte maturation, speeding up antral formation [44], favoring cell division and exhibiting a strong protective effect against atresia [45,46]. It is well known that the production of certain growth factors and peptides involved in the differentiation and mitosis of the granulosa cells, the oocyte, the endometrium and the embryo are estrogen-dependent [47,48].…”

Estrogen Receptor Null Mice: What Have We Learned and Where Will They Lead Us?

“…Therefore, as demonstrated for ER␣ by the ␣ERKO, ER␤ does not appear to be essential for the establishment of germ cell number or ovarian development. Several of the speculated intraovarian roles of estrogen were discussed previously and include a proposed critical role in proliferation of the granulosa cells in the maturing follicle (217)(218)(219)(220)231). However, the multiple large follicles present in the ␤ERKO ovaries indicate no marked differences in granulosa cell number.…”

“…Since then, numerous intraovarian effects of large amounts of locally synthesized estrogens have been described and postulated to be essential to normal follicular development and ovarian function. In granulosa cells of the growing follicle, estrogen has been reported to increase the levels of its own receptor (216), as well as induce DNA synthesis and proliferation (205,(217)(218)(219)(220), increase the number and size of intercellular gap junctions (221), stimulate synthesis of IGF-I (222), and attenuate apoptosis and follicular atresia (223,224). Estradiol is also known to augment the actions of FSH on granulosa cells, resulting in the maintenance of FSH-receptor levels (218,(225)(226)(227) and the acquisition of LH-receptor (218, 228 -231), an event critical to successful ovulation.…”