Chronic Elevation of Estradiol in Young Ovariectomized Rats Causes Aging-Like Loss of Steroid-Induced Luteinizing Hormone Surges

• Published in: Biology of reproduction Vol. 64; no. 2; pp. 684 - 688
• Main Authors: TSAI, Houng-Wei, LEGAN, Sandra J
• Format: Journal Article
• Language: English
• Published: Madison, WI Society for the Study of Reproduction 01-02-2001
• Subjects: Aging - blood; Animals; Biological and medical sciences; Estradiol - physiology; Female; Fundamental and applied biological sciences. Psychology; Luteinizing Hormone - blood; Mammalian female genital system; Morphology. Physiology; Ovariectomy; Progesterone - pharmacology; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Steroids - pharmacology; Vertebrates: reproduction; Ovariectomy; Rat; Ageing; Estrogen; Rodentia; Gonadotropin; Estradiol; Ovarian hormone; Vertebrata; Mammalia; Adenohypophyseal hormone; Luteinizing hormone; Female; Progesterone; Sex steroid hormone; Mechanism of action
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod64.2.684

This study was designed to test the hypothesis that the loss of LH surges in response to the stimulatory actions of estradiol
and progesterone in middle-aged, persistent-estrous (PE) rats may be caused by chronic elevations in circulating estradiol.
Five groups of regularly cycling young rats received an s.c. estradiol implant immediately after ovariectomy (Day 0). For
determination of LH surges, blood samples were collected hourly between 1200–1900 h from each of the five groups at one of
the following times: 3 days, or 1, 2, 4, or 8 wk later. On the next day, either progesterone (0.5 mg/100 g BW) or corn oil
was injected s.c. at 1200 h, and samples were obtained as before. Incidence and amplitude of estradiol-induced LH surges decreased
during the first 2 wk of estradiol treatment, after which no surges occurred. Progesterone enhanced the incidence and amplitude
of estradiol-induced LH surges thus delaying their disappearance. These results support our hypothesis and demonstrate that
the stimulatory actions of estradiol and progesterone on the LH surge sequentially diminish with time after exposure to estradiol
in young rats. Thus, young rats chronically treated with estradiol may be a useful model for studying the mechanisms whereby
LH surges are abolished in middle age during the hyperestrogenic state of PE.