Authors: Johnson DW; Barnes MA; Akers RM; Pearson RE
Abstract: 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)
Keywords: Animals; Bromocriptine/pharmacology; Cattle/blood/*metabolism; D-Ala(2),MePhe(4),Met(0)-ol-enkephalin/pharmacology; Dopamine/*physiology; Endorphins/*pharmacology; Female; Prolactin/*blood; Random Allocation; Thyrotropin-Releasing Hormone/pharmacology|
Journal: Journal of animal science Volume: 69 Issue: 11 Pages: 4545-51 Date: Nov. 1, 1991 PMID: 1752829 |
Johnson DW, Barnes MA, Akers RM, Pearson RE (1991) Exogenous opioids increase plasma prolactin in Holstein calves primarily via a dopaminergic mechanism. Journal of animal science 69: 4545-51.
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