Location: Forage-animal Production ResearchTitle: Bovine lateral saphenous veins exposed to ergopeptine alkaloids do not relax) Author
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2013
Publication Date: 2/3/2014
Citation: Pesqueira, A., Harmon, D.L., Branco, A.F., Klotz, J.L. 2014. Bovine lateral saphenous veins exposed to ergopeptine alkaloids do not relax. Journal of Animal Science. 92:1213-1218. Interpretive Summary: Tall fescue (Lolium arundinaceum) is commonly infected with the endophytic fungus Neotyphodium coenophialum. This fungus produces numerous ergot alkaloids that cause vasoconstriction, a primary sign and cause of symptoms of the fescue toxicosis syndrome, in grazing animals. These alkaloids can be classified by their chemical structure into two groups, ergoline alkaloids and ergopeptine alkaloids. Previous research has reported a persistent contractile response to ergotamine and ergovaline in core and peripheral bovine vasculature has been previously demonstrated. Because N. coenophialum produces numerous ergot alkaloids, the objective of this study was to observe the contractile response patterns of the lateral saphenous vein to single additions of lysergic acid, lysergol, ergonovine, ergocryptine, ergocornine, ergocristine, ergotamine, and a tall fescue seed extract using a multimyograph. In conclusion, this study indicated that ergot alkaloids classified as ergolines do not have a persistent binding effect and do not cause a sustained contractile response in the cranial branch of the bovine lateral saphenous vein. The contractile response caused by ergolines is highest during the first 15- to 30-min interval followed by constant relaxation during the remaining 120-min incubation period. Obversely, the ergopeptine alkaloids have a sustained contractile response that slowly increased during the first three to five 15-min intervals. Further, the ergopeptines did not relax markedly during the incubation period. To mitigate the vascular effects of fescue toxicosis, future research should be direct at analyzing the ergot alkaloid receptor affinity mechanism, and how to manipulate this effect.
Technical Abstract: The ergot alkaloid ergovaline has demonstrated a persistent and sustained contractile response in several different vascular models. It was hypothesized that different alkaloids isolated from tall fescue (Lolium arundinaceum) will contribute to this contractile response differently. The objective was to compare contractile-response patterns of single additions of 1 × 10-4 M lysergic acid (LSA), lysergol (LYS), ergonovine (ERN), ergotamine (ERT), ergocristine (ERS), ergocryptine (ERP), ergocornine (ERO) and 1 × 10-6 M ergovaline (tall fescue seed extract; EXT). Lateral saphenous veins were collected from 6 Holstein steers (BW = 397 ± 28 kg) immediately after slaughter, sliced into cross-sections, and suspended in myograph chambers containing oxygenated Krebs-Henseleit buffer (95% O2/5% CO2; pH = 7.4; 37°C). Treatments were added at 0 min and buffer was replaced in 15-min intervals for a 120-min incubation. In addition to maximum tension and time to reach maximum tension, percent relaxation and rate of relaxation were determined following maximum tension for each treatment. All compounds tested produced significant contractile responses (P < 0.05). Ergoline alkaloids, LSA, LYS, and ERN reached maximum response in less time (P < 0.05) than the remaining compounds and began to relax immediately after first buffer change. Lysergic acid had the greatest (P < 0.05) percent relaxation and ERN had the greatest (P < 0.05) rate of relaxation. The EXT, ERT, ERS, ERP, and ERO all had slower developing contractile responses with a longer (P < 0.05) interval until maximum tension was achieved compared to ERN, LSA, and LYS. Maximal responses to these ergopeptine alkaloids, however, all persisted for the 120-min duration with negligible relaxation occurring. The structural classes of alkaloids differed greatly in the type of contractile response generated in the lateral saphenous vein. Persistence of contractile response is thought to be the primary contributing factor to the vasoconstriction observed in animals demonstrating signs of fescue toxicosis, where different ergot alkaloids can contribute differently.