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Regular Article |
a Departments of Obstetrics & Gynecology, Biology, and Neurobiology and
b the Laboratory of Neuroendocrinology of the Brain Research Institute, University of California, Los Angeles, Los Angeles, California 90095
ABSTRACT
This study examined the influences of aging and reduced ovarian follicular reserve on estrous cyclicity, estradiol (E2) production, and gonadotropin secretion. Young virgin and middle-aged (MA) retired breeder female rats were unilaterally ovariectomized (ULO) or sham operated (control). Unilateral ovariectomy of young rats reduced the ovarian follicular reserve by one-half, to a level similar to that found in MA controls. Unilateral ovariectomy of MA females reduced the follicular pool further, to one half of MA controls. The incidence of regular cyclicity was significantly lower in MA ULO females than in young controls, with intermediate cycle frequency in young ULO and MA controls. Among cyclic rats, the magnitude of the proestrous LH surge was highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. Similarly, ovulation rates were highest in young controls, intermediate in young ULO rats and MA controls, and lowest in MA ULO females. While young ULO rats exhibited augmented secondary FSH surges on estrous morning, middle-aged ULO females displayed secondary FSH levels comparable to young controls. The effects of age and reduced follicle number on estrous cyclicity and gonadotropin secretion were not due to altered E2 secretion, as preovulatory E2 levels were similar among all groups. Thus, experimental reduction in the follicular reserve exerts acute effects on the preovulatory LH surge, ovulation rate, and estrous cyclicity in both young and MA rats. However, decreased follicle number increases FSH levels only in young rats, indicating aging-related alterations in the feedback regulation of FSH.
First decision: 16 October 2000.
1 This study was supported by NIH grants AG04810 and AG10620, awarded by the National Institute on Aging. C.R.A. was a Predoctoral Trainee supported in part by a Supplement to NIH grant AG04810.
2 Correspondence: Philip S. LaPolt, Department of Biology & Microbiology, 5151 State University Drive, California State University, Los Angeles, CA 90032. FAX: 323 343 6451; plapolt{at}calstatela.edu
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