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  • Title: Proestrous hormone surges dissociated from ovulation in the estrogen-treated hamster.
    Author: Greenwald GS.
    Journal: Endocrinology; 1975 Oct; 97(4):878-84. PubMed ID: 1193010.
    Abstract:
    Hamsters injected sc with 50 mug estradiol cyclopentylpropionate (ECP) at 0900 h on day 1 (metestrus) of the cycle show the normal "postovulatory" vaginal discharge 4 days later but do not resume ovulation until 14--18 days later. After ECP injection ovarian histology reveals that the follicles normally destined to ovulate at the end of the cycle (developing follicles) are healthy on the afternoon of day 1, but atretic by day 2. Developing follicles (8--12 granulosal layers) reappear by the afternoon of day 3; follicular development is still retarded by the afternoon of proestrus (day 4). Serum hormone levels were determined by RIA in ECP and oil treated hamsters. ECP fails to affect the normally high levels of FSH present throughout day 1; however, by day 2 both FSH and LH levels are usually undetectable. On day 3, a "rebound" phenomenon occurs and FSH and LH are now detectable in the ECP treated groups. The preovulatory increase of LH occurs on day 4 between 1200 and 1400 h in both groups whereas FSH increases at 1400 h in the ECP group but not until 1600 h in the controls. The elevated levels of FSH, usually observed throughout day 1, occur in the oil treated but not in the ECP group. This most likely accounts for the long delay before ovulation is resumed in the ECP group. Luteal function is unaffected by ECP; circulating levels of progesterone (P) are approximately 12 ng/ml on days 1 and 2 in both groups. The normal secretion of P on day 4 occurs in ECP and oil groups and in the absence of large antral follicles in the former animals. In the ECP group estradiol levels on days 1, 2, 3, 4 at 1500 h are 250, 263, 255, and 273 pg/ml respectively, compared to 34, 80, 105, and 297 pg/ml for the controls. These experiments demonstrate a) that the preovulatory release of anterior pituitary hormones on day 4 is normal in the ECP group but there are no follicles competent to respond by ovulating; b) that the continued functional activity of the CL in the face of elevated estrogen levels accounts for the maintenance of the 4 day "cycle"; and c) the extreme resistance to exogenous estrogen of the hamster as compared to the rat.
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