J. Anim Sci.
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J. Anim Sci. 1978. 46:1066-1070.
© 1978 American Society of Animal Science
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Glucocorticoid Secretion in Heifers Given Prostaglandin F2{alpha} after Triamcinolone Acetonide Pretreatment1

J. N. Stellflug2, T. M. Louis3 and H. D. Hafs

Michigan State University4, East Lansing 48824

Abstract

Two experiments were conducted to determine whether prostaglandin F2{alpha} (PGF2{alpha}) overcomes blockade of glucocorticoid secretion induced by pretreatment with triamcinolone acetonide (TA). In the first, nine diestrous heifers were assigned three each to be given (im) saline, 25 mg PGF2{alpha} or 25 mg PGF2{alpha} at 7 days after 22 mg TA (sc) pretreatment. Nine ovariectomized heifers were assigned to similar treatments, but the effect of TA or PGF2{alpha} on serum glucocorticoid was uninfluenced by ovariectomy. Serum glucocorticoid declined from 18 ng/ml to .2 ng/ml within 24 hr after TA, and remained less than 1.5 ng/ml for at least 7 days. Pretreatment with TA reduced peak glucocorticoid after PGF2{alpha} from 50 ng/ml to 6 ng/ml, but the increased glucocorticoid after PGF2{alpha} was significant in TA-pretreated heifers. At 12 hr after PGF2{alpha} treatment, peak glucocorticoid secreted in response to 5,000 IU ACTH (sc) was reduced from 60 ng/ml in controls to 20 ng/ml in TA-pretreated heifers.

The second experiment was conducted with 18 heifers to compare glucocorticoid secretion after PGF2{alpha} (5 mg) or ACTH (200 IU) given intravenously, with or without TA (20 mg, sc) pretreatment 6 hr earlier. Without TA pretreatment, serum glucocorticoid increased to about 30 ng/ml within 30 min after PGF2{alpha} and ACTH alike. Thereafter, the response to ACTH was higher (60 vs 30 ng/ml) and more prolonged (10 vs 2 hr) than after PGF2{alpha}. Pretreatment with TA reduced peak glucocorticoid by 50% after ACTH, but it essentially abolished the response to PGF2{alpha}. Therefore, the principal action of PGF2{alpha} to cause increased serum glucocorticoid probably is on the pituitary or hypothalamus.

Footnotes

1 Published with approval of Director of the Agricultural Experiment Station as Paper No. 8207. This was supported in part by USPHS Research Grant No. 06948. PGF2ª Tham salt was provided by Dr. J. W. Lauderdale, The Upjohn Co.

2 Present address: U.S. Sheep Research Station, Dubois, ID 83423.

3 Present address: Department of Anatomy, East Carolina Medical School, Greenville, NC 27834.

4 Department of Dairy Science.






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Copyright © 1978 by the American Society of Animal Science.