J. Anim Sci.
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J. Anim Sci. 1972. 35:801-804.
© 1972 American Society of Animal Science
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Changes in Hypothalamic Biogenic Amines and Serum LH in the Ewe during the Estrous Cycle1

J. E. Wheaton, Susan K. Martin, L. V. Swanson and F. Stormshak2, 3,

Oregon State University, Corvallis 973314

Abstract

EIGHTEEN mature Hampshire and Suffolk ewes were checked for estrus at 0400, 0800, 1200 and 1600 daily using vasectomized rams and assigned to one of three groups. The experimental groups were as follows: group 1, ewes sacrificed on day 12 of the cycle (first day of estrus=day zero of the cycle); group 2, ewes sacrificed 4 hr. after being detected in estrus at 1200; and group 3, ewes sacrificed 8 hr. after being detected in estrus at 0800. On the day of sacrifice, blood samples were taken from each ewe at 0800 (except from ewes in group 2), 1200 and just prior to sacrifice at 1600. The pituitary, median eminence, hypothalamus proper and mammillary body were removed from each ewe. Blood serum and the anterior pituitary were analyzed for luteinizing hormone (LH) by use of radioimmunoassay. The median eminence, hypothalamus proper and mammillary body were analyzed for serotonin and norepinephrine by use of spectrofluorometry.

Serotonin in the median eminence was lower in ewes of group 2 than ewes of either group 1 or 3 (P<.O5). The concentration of serotonin in the hypothalamus proper of ewes tended to be greater on day 12 than on the first day of estrus (P{cong}.08). Stage of the cycle was without effect on serotonin in the mammillary body. Norepinephrine in the hypothalamus proper and mammillary body was not altered significantly by stage of the estrous cycle. Norepinephrine was not detected in the median eminence. Serum LH was base-line in all ewes of group 1 and elevated in one-third of the ewes in group 2 and all of the ewes in group 3. Pituitary LH content and concentration did not change significantly during the stages of the estrous cycle studied.

The data suggest that release of pituitary LH in the ewe is dependent upon a prior reduction of serotonin in the hypophysiotropic area of the brain.

Footnotes

1 Technical Paper No. 3254, Oregon Agricultural Experiment Station.

2 This investigation was supported by a special grant (No. 016-15-03) from the Cooperative State Research Service, C.S.D.A.

3 Appreciation is expressed to the Endocrinology Study Section, National Institute of Health for the gift of NIH-LH-S17, Dr. G. D. Niswender for the anti-ovine LH serum and Dr. L. E. Reichert for the highly purified ovine LH (LER-1056-C2) which were used for LH radioimmunoassay. The authors gratefully acknowledge the assistance of Mr. Steve Ford.

4 Department of Animal Science.






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Copyright © 1972 by the American Society of Animal Science.