|Foote, Andrew -|
|Harmon, David -|
|Mcleod, Kyle -|
|Bush, Lowell -|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 24, 2011
Publication Date: January 15, 2012
Citation: Foote, A.P., Harmon, D.L., Brown, K.R., Strickland, J.R., Mcleod, K.R., Bush, L.P., Klotz, J.L. 2012. Constriction of bovine vasculature by endophyte-infected tall fescue seed extract is similar to pure ergovaline. Journal of Animal Science. 90:1603-1609. Interpretive Summary: A formidable challenge for animal research in the problem area of fescue toxicosis is that the desired ergot alkaloids are unavailable in the required quantities. Using tall fescue seed provides an alternative to chemical pure alkaloid treatments, but alkaloid concentrations in seed are not constant from lot to lot or year to year. A tall fescue seed extract was generated to provide a large scale and consistent source of desired ergot alkaloids for animal studies pertaining to fescue toxicosis. Preliminary experiments demonstrated that an extract of endophyte-infected tall fescue seed (E+EXT) diluted based on ergovaline concentration induces a greater contractile response in ruminal artery and vein preparations in vitro than pure ergovaline. Findings from this experiment led to the development of a hypothesis that the presence of ergot alkaloids other than ergovaline in the extract are responsible for the increased contractile response. The objective of the current experiment was to determine if the greater contractility produced by the extract is attributed to the presence of the other ergot alkaloids. This was accomplished by using the bovine lateral saphenous vein, right ruminal artery, and right ruminal vein bioassays, representing peripheral and core vasculature, to compare an endophyte-free tall fescue seed extract (E-EXT), E+EXT, ergovaline alone, and a mixture of commercially available ergot alkaloids (ALK) made to mimic the E+EXT alkaloid concentrations. Data from these experiments indicate that an extract of endophyte-infected tall fescue seed is capable of inducing a contractile response similar to a mixture of ergot alkaloids and ergovaline alone. Results support ergovaline as being primarily responsible for vasoconstriction, especially in the peripheral vasculature.
Technical Abstract: Ergovaline has been extensively used to study vasoactive effects of endophyte- (Neotyphodium coenophialum) infected tall fescue (Lolium arundinaceum). However, preliminary in vitro tests indicated that an extract of toxic tall fescue seed (E+EXT) is more potent than ergovaline alone in a right ruminal artery and vein bioassay. This led to a hypothesis that other compounds in the seed extract contribute to vasoconstriction. Thus, experiments were conducted to determine if vasoactivity of an E+EXT is different than a mixture of ergot alkaloids (ALK; ergovaline, ergotamine, ergocristine, ergocryptine, ergocornine, ergonovine, and lysergic acid) of equal concentrations and to determine if an endophyte-free tall fescue seed extract (E-EXT) is vasoactive. Segments of lateral saphenous vein and right ruminal artery and vein were collected from Holstein steers (n = 6) shortly after slaughter. Vessels were cleaned of excess connective tissue and fat and sliced into segments that were suspended in a multi-myograph chamber with 5 mL of continually oxygenated Krebs-Henseleit buffer, equilibrated for 90 min, and exposed to a reference compound (120 mM KCl for ruminal vessels and 0.1 mM norepinephrine for saphenous vein). Increasing concentrations of each treatment (E+EXT, E-EXT, ALK, and ergovaline) were added to the respective chamber every 15 min following buffer replacement. Data were normalized as a % of maximal contractile response of the reference compound and fit to a sigmoidal concentration response curve. Ergovaline, ALK, and E+EXT induced similar responses in the saphenous vein, ruminal artery, and ruminal vein. The E+EXT displayed a smaller EC50 in the saphenous vein and ruminal vein (P < 0.008) but not ruminal artery (P = 0.31). Extrapolated Emax was greatest in the saphenous vein for ergovaline, lowest for E+EXT, and intermediate for ALK (P < 0.0001). E-EXT did not induce a contractile response in any vessel tested (P > 0.1). Data from this study indicate that ergovaline is responsible for the locally induced vasoconstriction of bovine vasculature.