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Biology of Reproduction, Vol 21, 793-800, Copyright © 1979 by Society for the Study of Reproduction
1 Department of Reproductive Medicine,
University of California, San Diego,
La Jolla, California 92093 Changes in uterine weight, morphology and estrogen receptor levels were studied in aging female
rats. The uterine weight (534 ± 31 mg; mean ± SEM) in rats during early constant estrus at 12
months of age was comparable to that of young proestrous rats. A marked increase in uterine
weight to 933 ± 135 mg occurred in late estrus at 24 months of age primarily as the result of an
increase in the luminal fluid content. Histological examination of these uteri indicated the presence
of tall proliferative luminal epithelium and thickened stromal and myometrial components, suggesting stimulation of the uterus by estrogen during constant estrus. A decrease in uterine weight
to 344 ± 20 mg was observed in aging rats during persistent diestrus at 30 months of age. These
uteri were characterized by low cuboidal luminal epithelia and secretory uterine stroma. Spontaneous formation of decidual tissue was also detected in some rats. These observations suggested
that the uterine tissue in persistent diestrous rats was probably under progestin influence. Independent of the marked changes in uterine morphology in aging rats, an age related decrease
in estrogen receptor content was detected in the uteri of the aging rats. Estrogen receptor content/
uterus decreased with increasing age from 8.0 pmoles in young proestrous rats at 4 months to
4.5, 3.1 and 1.1 pmoles in rats at 12, 24 and 30 months of age, respectively. Expressed as estrogen
binding sites/cell, a similar age related decrease in receptor concentration was observed in aging
rat uterus with a decrease from 9,300 sites/cell at 4 months to 5,200, 3,700 and 2,200 sites/cell
in aging rats at 12, 24 and 30 months of age, respectively. In contrast, no age related change in the
dissociation constant of nuclear estrogen receptor was detected (Kd = 1.4 ± 0.5 x 10-9 M). The present study demonstrates a decrease of uterine estrogen receptor content in female rats
with advancing age. The marked decrease in uterine estrogen receptor in old rats may contribute to
some adverse changes in uterine function resulting in an increased incidence of pregnancy failure.
Note:
ACKNOWLEDGMENTS
We thank June Gutierrez for her excellent technical assistance and Mrs. Cheri Anderson for typing
the manuscript.
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