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Ergovaline-induced vasoconstriction in an isolated bovine lateral saphenous vein bioassay¹

J. L. Klotz^*, L. P. Bush, D. L. Smith, W. D. Shafer, L. L. Smith^*, B. C. Arrington and J. R. Strickland^*,2

^* Forage-Animal Production Research Unit, USDA-ARS, Lexington, KY 40546; and Department of Chemistry, Eastern Kentucky University, Richmond 40475; and and Department of Plant and Soil Science, University of Kentucky, Lexington 40546

² Corresponding author: jstrickland{at}ars.usda.gov

Ergovaline has been proposed as a toxic component of endophyte-infected tall fescue. As many of the symptoms of fescue toxicosis are a result of compromised circulation, the objective of this study was to examine the vasoconstrictive potentials of ergovaline and a more documented ergopeptine, ergotamine, using a bovine, lateral (cranial branch) saphenous vein bioassay. Segments of the cranial branch of the lateral saphenous vein (2 to 3 cm) were collected from healthy, mixed breed cattle (n = 12 and n = 5 for the ergovaline and ergotamine experiments, respectively) at local abattoirs. The veins were trimmed of excess fat and connective tissue, sliced into 2- to 3-mm cross sections, and suspended in a myograph chamber containing 5 mL of a modified Krebs-Henseleit, oxygenated buffer (95% O₂ + 5% CO₂; pH = 7.4; 37°C). The tissue was allowed to equilibrate at 1 g of tension for 90 min before of the addition of treatments. Increasing doses of ergovaline (1x10^–11 to 1 x10^–4 M) or ergotamine (1 x10^–11 to 1 x 10^–5 M) were administered every 15 min after buffer replacement. Contractile response data were normalized to a percentage induced by a reference dose of norepinephrine (1 x10^–4 M). Contractile responses of saphenous veins were similar for ergovaline and ergotamine. Initial contractile responses began at 1 x10^–8 M for both ergovaline and ergotamine (4.4 ± 0.8% and 5.6 ±1.1%, respectively). Vascular tension continued to increase as the alkaloid concentrations increased (maximums: 43.7 ±7.1% at 1 x10^–5 M ergotamine; 69.6 ± 5.3% at 1 x10^–4 M ergovaline). Interestingly, ergovaline-induced contractions (1 x10^–4 M) were not reversed by repeated buffer replacement over a 105-min period. As previously shown with ergotamine, these results confirm that ergovaline is a potent vasoconstrictor. The resistance of an ergovaline-induced contraction to relaxation over an extended period of time suggests a potential for bioaccumulation of this ergopeptine alkaloid and may aid in understanding its toxicity within the animal.

Key Words: alkaloid • bovine • ergovaline • ergotamine • fescue • vasoconstriction

This article has been cited by other articles:

				J. L. Klotz, B. H. Kirch, G. E. Aiken, L. P. Bush, and J. R. Strickland Effects of selected combinations of tall fescue alkaloids on the vasoconstrictive capacity of fescue-naive bovine lateral saphenous veins J Anim Sci, April 1, 2008; 86(4): 1021 - 1028. [Abstract] [Full Text] [PDF]