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Biology of Reproduction, Vol 24, 784-794, Copyright © 1981 by Society for the Study of Reproduction
1 The Andrus Gerontology Center and the Department of Biological Sciences,
University of Southern California,
Los Angeles, California 90007 Midday plasma concentrations of estradiol (E2) and progesterone (P) were measured in aging
C57BL/6J mice showing either prolonged estrous cycles or persistent vaginal cornification (PVC).
In younger mice (5.5-7.5 months), the modal cycle length was 4 days, and the profiles of these
hormones during the cycle were similar to those previously reported. By 10-12.5 months, the modal cycle length had increased to 5 days. Although midday levels of
P were unimpaired at this age, the profile of E2 was markedly altered. Proestrus (Day 1) and estrus
(Day 2) levels of E2 were indistinguishable from those of younger mice, but basal values on Day 3
and the preovulatory rise beginning on Day 4 were reduced in older mice by 80% and 45%, respectively. As a result, attainment of preovulatory levels of E2 equivalent to those of younger mice was
delayed by about 1 day, which corresponded to the average net increase in median cycle length at
this age. In 14-month-old PVC mice, levels of E2 were comparable to the basal values of younger cycling
mice and threefold greater than ovariectomized values. However, P levels were 50% lower than
basal values in cycling mice and indistinguishable from values in ovariectomized mice. Consequently, the E2:P ratio was elevated nearly twofold in PVC mice. Because transient experimental suppression of the preovulatory rise of E2 lengthens estrous
cycles in young rodents, we hypothesize that the delayed rise of E2 in older mice contributes to
their prolonged cycles. In addition, the increased E2:P ratio in PVC mice creates a relatively
unopposed estrogenic milieu which may accelerate the development of the pituitary tumors and
hypothalamic dysfunction that characterize aged female mice.
Note:
ACKNOWLEDGMENTS
We thank L. C. Brown, D. Jacobson. and D. Meza
for assistance in data analysis, and G. Kendrick for
excellent care of the mouse colony. We are grateful to
Drs. R. G. Gosden, C. F. Holinka, H. S. Huberman,
and B. S. Schachter for their critical reviews of this
manuscript.
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