J. Anim Sci.
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J. Anim Sci. 1986. 63:162-168.
© 1986 American Society of Animal Science
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Regulation of Pulsatile LH Secretion by Ovarian Steroids in the Heifer1

K. Imakawa, M. L. Day, D. D. Zalesky, M. Garcia-Winder, R. J. Kittok and J. E. Kinder2,3,

University of Nebraska4, Lincoln 68583

Abstract

Two experiments were conducted to evaluate relationships among luteinizing hormone (LH), estradiol-17β (E2) and progesterone secretion during the preovulatory period in the heifer after prostaglandin F2{alpha} (PGF2{alpha}-induced regression of the corpus luteum. A second objective was to elucidate the effects of E2 in regulating LH secretion. In Exp. 1, LH, E2 and progesterone concentrations were determined in serial samples collected during the preovulatory period after PGF2{alpha}-induced luteal regression in five Red Angus x Hereford heifers. Progesterone declined to 1 ng/ml by 12 h after the second injection of PGF2{alpha}. Frequency of LH pulses increased linearly (P<.01), whereas no change in amplitude of LH pulses was detected before the preovulatory LH surge. This resulted in a linear increase (P<.01) in mean LH concentrations. Estradiol also increased in a linear manner (P<.01), and the rise in E2 was parallel to the increase in mean LH concentrations. In Exp. 2, 12 Angus x Hereford heifers were ovariectomized and administered either 13.5- or 27-cm silastic implants containing E2 at ovariectomy. Four heifers served as nonimplanted controls. Thirty-one days after ovariectomy all heifers were bled at 12-min intervals for 6 h. Frequency of LH pulses declined linearly (P<.03) while mean LH (P<.09) and pulse amplitude (P<.01) increased linearly as E2 dose increased. These results indicate that a reduction in progesterone increases the frequency of LH pulses during the follicular phase of the estrous cycle in cattle. Estrogen seems to enhance total LH output from the pituitary during the preovulatory period by maintaining the amplitude of LH pulses during the period when frequency of LH pulses is increasing as a result of decreased progesterone brought on by the regression of the corpus luteum.

Footnotes

1 Published as Paper No. 7925, Journal Series, Nebraska Agr. Res. Div.

2 Send requests to this author, 218 Marvel Baker Hall.

3 Acknowledgement is made to Jane A. Ossenkop and Cheryl C. Rieck for assistance in preparation of the manuscript, John C. Fudge for assistance in data collection, Dennis R. Brink for assistance in preparation of diets, Kenneth A. Pearson for technical assistance in laboratory procedures, Scott G. Kurz for assistance in preparation of figures and Merlyn K. Nielsen for assistance in analysis of data. We also thank Dr. J. J. Reeves for the LH antisera, Dr. N. Mason for the E2 antisera and Dr. L. E. Reichert for the purified LH used for iodination,

4 Dept. of Anim. Sci.






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Copyright © 1986 by the American Society of Animal Science.