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Biology of Reproduction, Vol 23, 345-351, Copyright © 1980 by Society for the Study of Reproduction
1 Department of Obstetrics-Gynecology, Department of Anatomy,
and the Brain Research Institute,
University of California, Los Angeles School of Medicine,
Los Angeles, California 90024 The stimulatory feedback actions of estradiol and progesterone on gonadotropin secretion were
tested in acutely ovariectomized (OVX) old constant estrous (CE) and pseudopregnant (PSP) rats of
similar age (20-26 months). Studies were also performed to determine the pituitary LH responses
to synthetic LH-releasing hormone (LHRH) in both intact and OVX, estradiol-implanted CE and
PSP females. Serial blood samples were collected through chronic intra-atrial cannulae for measuring plasma LH and FSH, while single blood samples were obtained for estrogen and progestin
assays. Serum concentrations of estradiol were twice as high in CE (26 ± 3 pg/ml, mean ± SEM) as in
PSP rats (11 ± 2 pg/ml), whereas progesterone and 20 Despite these differences between the CE and PSP states, the pituitary LU responses to single
i.v. pulses of LHRH were the same in intact CE and PSP rats. Placement of estradiol implants into
OVX-CE and PSP rats significantly increased serum estradiol concentrations in both groups, but
enhanced the LU response to LHRH only in the PSP rats and not in the CE animals. The present study demonstrates that the stimulatory feedback actions of estradiol and progesterone on LH secretion, which are present in acutely OVX old PSP rats, are absent in old CE
females immediately following ovariectomy. Together with other data the results suggest changes
in central nervous function of CE rats, which are probably related to their ovarian steroid background rather than to advanced age per se.
-hydroxyprogesterone levels were many-fold
greater in PSP than in CE rats. In acutely OVX-PSP rats, estradiol and progesterone administration
elicited a significant increase in LH release. PSP females that had evidence of pituitary tumors
and/or lesions showed an LH response to ovarian steroids similar to that of animals with normal
pituitaries. In contrast, steroid administration failed to increase LH release in acutely OVX-CE rats,
and this lack of LH response was found in animals regardless of whether pituitary pathology
was evident.
Note:
ACKNOWLEDGMENTS
The authors especially thank Ms. Peggy Chappus
for invaluable assistance in conducting these experiments. We gratefully acknowledge Drs. A. S. Bhatnagar and G. E. Abraham for generous gifts of steroid
hormone antisera, Dr. David Whitmoyer for help with
the gonadotropin RIAs, Ms. Arlene Koithan for the
excellent histological preparations, Mr. Bob McAlister
for the illustrations, Ms. Marianne Lu for help with the
steroid RIAs, and Ms. Marsha Greenstein, Ms. Kathi
Gullam, and Ms. Lois Fels for cheerful assistance in
the preparation of this manuscript.
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