Effect of ergot alkaloids on contractility of bovine right ruminal artery and vein.

Abstract

Ergot alkaloids produced by the endophyte (Neotyphodium coenophialum) associated with tall fescue (Lolium arundinaceum) are implicated in the clinical signs of fescue toxicosis. These compounds were hypothesized to correspondingly affect foregut vasculature. The objective of this study was to determine vasoconstrictive potentials of ergovaline, ergotamine, ergocryptine, ergocristine, ergonovine, ergocornine, and lysergic acid on right ruminal artery and vein. Segments of right ruminal artery and vein were collected from the ventral coronary groove of predominantly Angus heifers (n = 10) shortly after slaughter and placed in a modified Krebs-Henseleit buffer on ice. Vessels were cleaned of excess connective tissue and fat, sliced into 2- to 3-mm segments, and suspended in a multi-myograph chamber with 5 mL of continuously oxygenated Krebs-Henseleit buffer (95%O(2)/5% CO(2); pH 7.4; 37°C). Arteries and veins were equilibrated to 1.0 and 0.5 g, respectively, for 90 min followed by the reference addition of 120 mM KCl. Increasing concentrations of each alkaloid were added to the respective chamber every 15 min after buffer replacement. Data were normalized as a percentage of the contractile response induced by KCl. Alkaloid (P < 0.0001), concentration (P < 0.0001), and vessel type (artery or vein; P = 0.004) affected contractility. No arterial response was observed until 10(-6) M for ergovaline and ergotamine; 10(-5) M for ergocryptine, ergocornine, and ergonovine; and 10(-4) M for ergocristine. Lysergic acid did not induce a contractile response in the ruminal artery. No venous contractile response was observed until concentrations of 10(-6) M for ergovaline, 10(-5) M for ergotamine, and 10(-4) M for ergocryptine and ergocristine were achieved. Lysergic acid, ergonovine, and ergocornine did not induce a contractile response in the ruminal vein. A greater arterial maximal response was observed for ergovaline (P < 0.0001), whereas the arterial and venous responses were not different for ergotamine (P = 0.16), ergocryptine (P = 0.218), and ergocristine (P = 0.425). These results indicate that ergot alkaloids associated with toxic endophyte-infected tall fescue are vasoactive and can potentially alter arterial blood supply and venous drainage from the bovine foregut.