J. Anim Sci.
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J. Anim Sci. 1983. 57:443-448.
© 1983 American Society of Animal Science
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Luteinizing Hormone, Follicle Stimulating Hormone ad Prolactin Secretion in Ewes and Wethers after Zeranol or Estradiol Injection

T. H. Elsasser, D. J. Bolt1, B. D. Bradley2 and M. Roper

Food and Drug Administration3, Beltsville, MD 20705

2 Reprint requests.

Abstract

Plasma concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) were determined over a 24-h period using radioimmunoassay in sheep injected with corn oil (control) or various doses of zeranol or estradiol-17β. Injection of .333, 1 or 10 mg of zeranol caused dose-related increases (P<.01) in plasma PRL (peak levels at 12 to 18 h) and LH (peak levels at 12 to 20 h) in ovariectomized ewes. Similarly, PRL and LH increased following doses of 33 or 100 µg of estradiol. Before the LH surge, plasma LH levels were significantly depressed (4 to 8 h). Plasma FSH levels were significantly decreased 4 to 8 h after zeranol and estradiol injection. Slight surges of FSH were observed at times similar to those of LH, but the peak level was never greater than control levels. Injection of 1 mg of zeranol or 100 µg of estradiol into wethers resulted in a 24-h pattern of PRL secretion not significantly different from the controls, a transient depression of LH concentration and significantly prolonged inhibition of FSH secretion. These results indicate similarities in the effects of zeranol and estradiol on anterior pituitary hormone secretion within groups of animals of the same sex or reproductive state. Differences in secretion and plasma concentrations of LH, FSH and PRL due to underlying sexual dimorphism are maintained and expressed even when animals are challenged with structurally different compounds of varying estrogenic potencies.

Footnotes

1 Reprod. Lab., Animal Science Institute, USDA, Beltsville, MD 20705.

3 Division of Vet. Med. Res., Bureau of Vet. Med.






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Copyright © 1983 by the American Society of Animal Science.