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Biology of Reproduction, Vol 24, 323-331, Copyright © 1981 by Society for the Study of Reproduction
1 Medical Research Centre, Prince Henry’s Hospital,
Melbourne, 3004, Australia Estrogen receptors (ER) in the neuroendocrine tissues of female sheep have been studied with
respect to breed, season, and stage of the estrous cycle. In the first study, cytoplasmic ER measured by Scatchard analysis in neuroendocrine tissues from seasonally breeding Merino x Border
Leicester (Crossbred) ewes demonstrated no seasonal variation in the pineal, pituitary, and cerebral
cortex; in contrast, total cytoplasmic ER levels in the hypothalamus were almost twofold higher
(31.5 ± 2.7 fmoles/mg protein; mean ± SEM) in anestrous ewes than in cycling ewes (18.5 ± 2.7
fmoles/mg protein). In a second study, cytoplasmic and nuclear ER levels were measured in pituitary glands from
Crossbred ewes in anestrus and Merino and Crossbred ewes during the luteal and follicular phases
of the estrous cycle. Cytoplasmic ER levels during the luteal phase were significantly (P<0.005)
higher in Crossbred ewes (9717 ± 952 fmoles/g wet wt; mean ± SEM) than in Merino ewes (5477 ±
858 fmoles/g wet wt). In both breeds, nuclear ER levels were significantly (P<0.001) higher during
the follicular phase (Crossbred, 1052 ± 147; Merino, 841 ± 156) than during the luteal phase
(Crossbred, 292 ± 31; Merino, 394 ± 47). In Crossbred ewes nuclear ER levels during anestrus (347
± 55) were similar to luteal phase levels. These data indicate that hypothalamic control of the circannual breeding pattern in the sheep
may be related to ER levels. In the short term, during the estrous cycle, pituitary nuclear ER levels
reflect estrogen secretion. A breed difference in ER levels may have a fundamental genotypic basis
that explains breed disparities in responsiveness to estrogen.
Note:
ACKNOWLEDGMENTS
This study was carried out at the Animal Research
Institute, Werribee, Victoria, and we gratefully acknowledge the cooperation of Dr. Ian Cumming of the
Victorian Department of Agriculture. Technical
assistance of Mr. B. Doughton and Mrs. C. Cocks and
the financial assistance of the Australian Wool Research Trust Funds, the Ford Foundation, and the
National Health and Medical Research Council of
Australia is gratefully acknowledged.
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  C. J. Scott, A. J. Tilbrook, D. M. Simmons, J. A. Rawson, S. Chu, P. J. Fuller, N. H. Ing, and I. J. Clarke The Distribution of Cells Containing Estrogen Receptor-{alpha} (ER{alpha}) and ER{beta} Messenger Ribonucleic Acid in the Preoptic Area and Hypothalamus of the Sheep: Comparison of Males and Females Endocrinology, August 1, 2000; 141(8): 2951 - 2962. [Abstract] [Full Text] [PDF]
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D. C. Skinner and A. E. Herbison Effects of Photoperiod on Estrogen Receptor, Tyrosine Hydroxylase, Neuropeptide Y, and {beta}-Endorphin Immunoreactivity in the Ewe Hypothalamus Endocrinology, June 1, 1997; 138(6): 2585 - 2595. [Abstract] [Full Text] [PDF]
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