Endophytic fungal toxin effect on adrenergic receptors in lateral saphenous veins (cranial branch) of cattle grazing tall fescue.

Abstract

The objective of this research was to characterize the adrenergic receptor response in veins of cattle that grazed tall fescue (Festuca arundinacea Schreb.), with (E+) and without (E-) fungal endophyte (Neotyphodium coenophialum) infection. Measurement of contractile response of lateral saphenous veins to selective adrenergic receptor agonists (alphal, phenylephrine; alpha2, BHT-920) revealed enhanced reactivity (greater contractile response) only for the alpha2 adrenergic receptor in E+ pastured cattle. This response was consistent over a 3-yr grazing period. Significant contractility differences in response to BHT-920 occurred at concentrations of 3x10(-6) M and greater. Early research has reasoned that the enhanced reactivity is due to endophyte toxin effect on intracellular signaling systems. The enhanced contractile effect would alter blood flow dynamics and contribute to clinical signs and pathologic change in animals. The alpha2-adrenergic receptor is also involved in the control of many metabolic reactions. Thus, for drug therapy to be successful in reversing the adverse effects of E+ tall fescue exposure in cattle, effects on the alpha2-adrenergic tissue receptors must be neutralized.

Metabolomics of fescue toxicosis in grazing beef steers

“…Vasoconstrictive responses (Klotz et al, 2008;Oliver et al, 1993;Oliver et al, 1998;Rhodes et al, 1991) inducing perturbed nutrient absorption and metabolism (Egert et al, 2014a;Pesqueira et al, 2014) occur concurrently with altered circulating prolactin and cholesterol levels, which together with and intra-and extrahepatic enzyme activity changes, may play a role in the etiology of FT (Bacon, 1995;Rosenkrans and Ezell, 2015;Settivari et al, 2008;Thompson and Stuedemann, 1993;Zbib et al, 2014Zbib et al, , 2015. Foote et al (2013) suggested impaired weight gain might be attributed to a decrease in volatile fatty acid (VFA) absorption or production caused by increased ruminal EA concentration.…”

Fescue toxicosis

“…Other ergopeptine alkaloids, including ergotamine and bromocryptine, are also able to reproduce fescue toxicosis syndromes (Evans et al, 1999(Evans et al, , 2004bBlodgett, 2001). Ergovaline is a very potent vasoconstrictor in in vitro models (Oliver et al, 1998). In addition, ergovaline is also a strong prolactin inhibitor, whereas ergonovine, a lysergic acid amide in E fescue, is unable to produce typical signs of fescue toxicosis or lower prolactin concentrations in cattle (Oliver et al, 1994).…”

Ergovaline, an endophytic alkaloid. 1. Animal physiology and metabolism

“…McPherson and Beart (1983) reported a general selectivity for a2 receptors by ergot derivatives. Oliver et al (1998) evaluated a1 and a2 receptors in the lateral saphenous veins collected from cattle that had grazed endophyte-free and endophyte-infected tall fescue (ergovaline concentrations not provided). Using selective agonists, the a1-adrenergic response was not affected by pasture treatment, whereas the a2-adrenergic receptor responses where enhanced in veins collected from the endophyte-infected group of cattle.…”