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University of Kentucky, Lexington 40546-0215 and University of Georgia, Athens 30602
Abstract
An experiment was conducted to determine if the decrease in circulating concentrations of prolactin in cattle consuming endophyte (Acremonium coenophialum) -infected tall fescue (Festuca arundinacea) was associated with changes in prolactin concentrations in the anterior pituitary and concentrations of dopamine (DA) and its metabolites 3,4-dihydroxyphenyl-acetic acid (DOPAC) and homovanillic acid (HVA) in the stalk median eminence (SME), preoptic area (POA) and hypothalamus (HP). Six crossbred steers that grazed high-endophyte (> 90% infected) fescue and four steers that grazed low-endophyte (< 1% infected) fescue from April to September were slaughtered. Brains and pituitaries were removed and dissected. Extracts from neural tissue were analyzed for DA, DOPAC and HVA using high performance liquid chromatography/electrochemical detection. Pituitary extracts and sera from blood samples taken 5 d prior to slaughter were subjected to prolactin radioimmunoassay. Consumption of high-endophyte fescue was associated with decreased concentrations of prolactin in serum (P < .01) and in the anterior pituitary (P = .08), decreased (P < .05) concentrations of DA in the SME and decreased (P < .01) concentrations of HVA in the POA and HP, but it did not influence levels of DOPAC. These results suggest that endophyte toxins may reduce prolactin synthesis and release and may alter activity of dopaminergic neurons.
1 This paper (no. 87-5-92) is published with the permission of the Kentucky Agric. Exp. Sta.
2 Dept. of Anim. Sci., Univ. of Kentucky, Lexington 40506.
3 Dept. of Anim. Sci., Univ. of Georgia, Athens 30602.
4 The authors thank Gary L. Jackson, Univ. of Illinois, for prolactin antiserum; the National Hormone and Pituitary Program (NIADDKD) for providing highly purified prolactin; Karen Meekins and Susan Hays for technical assistance; Esther Collins for preparation of this manuscript; and Russ Muntifering for his editorial assistance.
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