J. Anim Sci.
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Journal of Animal Science, Vol 69, Issue 11 4545-4551, Copyright © 1991 by American Society of Animal Science

JOURNAL ARTICLE

Exogenous opioids increase plasma prolactin in Holstein calves primarily via a dopaminergic mechanism

D. W. Johnson, M. A. Barnes, R. M. Akers and R. E. Pearson
Virginia Polytechnic Institute and State University, Blacksburg 24061.

A study was conducted to determine whether exogenous opioids increase prolactin (PRL) secretion in Holstein heifer calves via a dopaminergic mechanism. Twenty-four Holstein heifer calves ranging in age from 5 to 7 mo were assigned to one of four treatment groups (six/treatment): 1) injection of saline (SAL); 2) injection of a synthetic enkephalin (D-Ala2, N-Me-Phe4, Met(O)5-ol enkephalin; DAMME); 3) injection of DAMME after pretreatment with the long-acting dopamine agonist 2-bromo-alpha-ergocryptine; or 4) injection of thyrotropin-releasing hormone (TRH) after pretreatment with 2-bromo-alpha-ergocryptine. Calves were equipped with indwelling jugular cannulas on d 1, and baseline plasma PRL concentrations were established. Animals receiving 2-bromo-alpha-ergocryptine were injected s.c. 3 h after the last baseline sample was drawn on d 1. On d 2, calves assigned to receive SAL, DAMME, or TRH were injected 2 h after the start of sampling, and sampling was continued for an additional 4.5 h. Basal plasma PRL was lower (P less than .01) on d 2 in calves injected with 2-bromo-alpha-ergocryptine than baseline levels on d 1. Plasma PRL was higher (P less than .01) in calves not pretreated with 2-bromo-alpha-ergocryptine after DAMME injection on d 2 but was not different after DAMME injection in calves pretreated with 2-bromo-alpha-ergocryptine. In contrast, plasma PRL increased (P less than .01) after TRH injection on d 2 in calves pretreated with 2-bromo-alpha-ergocryptine.(ABSTRACT TRUNCATED AT 250 WORDS)


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A. Ahmadzadeh, M. A. Barnes, F. C. Gwazdauskas, and R. M. Akers
Dopamine antagonist alters serum cortisol and prolactin secretion in lactating Holstein cows.
J Dairy Sci, June 1, 2006; 89(6): 2051 - 2055.
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Copyright © 1991 by the American Society of Animal Science.