J. Anim Sci.
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J. Anim Sci. 1987. 65:196-202.
© 1987 American Society of Animal Science
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Naloxone-Reversible Inhibition of Luteinizing Hormone in Postpartum Ewes: Effects of Suckling and Season1

P. V. Malven and R. E. Hudgens

Purdue University2 West Lafayette, IN 47907

Abstract

Involvement of endogenous opioids in inhibition of luteinteing hormone (LH) release and stimulation of prolactin (PRL) release was investigated by injecting the opioid antagonist naloxone into 18 ewes on d 7 and 8, d 12 and 13, and d 18 and 19 postpartum. Compared with control injections of saline, iv naloxone (1 mg/kg) increased serum concentrations of LH and decreased serum PRL in samples collected 15, 30 and 45 min after each injection. Ewes lambing in the spring (March) or autumn (September and October) that nursed one or two lambs did not differ in their LH and PRL responses to naloxone. Autumn-lambing ewes from which lambs were weaned within 1 d after parturition did not differ from ewes of the autumn-nursed group in any of the following characteristics: 1) serum LH increases following naloxone, 2) basal secretion of LH, 3) postpartum interval to first increase in serum progesterone and 4) relative decrease in serum PRL after naloxone despite large differences in basal PRL secretion. In summary, postpartum expression of a naloxone-reversible inhibition of LH release and stimulation of PRL secretion did not depend on suckling stimuli or differ between autumn and spring parturitions.

Footnotes

1 Published as journal paper no. 11,011, Purdue Univ. Agr. Exp. Station. The authors acknowledge the assistance of T. L. Roberson, S. A. Haglof, G. R. Kelly, M. E. Einstein, C. C. Chao and W. E. Trout.

2 Dept. of Anim. Sci.






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Copyright © 1987 by the American Society of Animal Science.