VASOCONSTRICTION IN BOVINE VASCULATURE INDUCED BY THE TALL FESCUE ALKALOID LYSERGAMIDE

Treatment of bovine lateral saphenous vein (cranial branch) and dorsal metatarsal artery with lysergamide (lysergic acid amide), an alkaloid in abundance in tall fescue, resulted in vasoconstriction similar to that previously shown for the ergot alkaloids ergonovine and ergotamin e. Preincubation of tissues with lysergamide resulted in partial inhib ition of the contractile response induced by the selective adrenergic agents phenylephrine and BHT-920 (P < .05), indicating partial agonist or antagonist activity of lysergamide at these receptors. Bovine vess els were strongly contracted by serotonin, and the response was marked ly inhibited (P < .01) when tissues were preincubated with lysergamide . Studies with selective serotonergic agents indicated that lysergamid e may have predilection for serotonin-2 receptors (5-HT2). Thus, lyser gamide by itself has vasoconstrictor activity and acts as a partial ag onist or antagonist at adrenergic and serotonergic receptors. Further studies are needed to establish the exact receptor effects of lysergam ide. However, it is evident that this important alkaloid found in tall fescue infested with the endophytic fungus Acremonium coenophialum sh ould be given consideration in studies designed to alleviate the fescu e toxicosis syndrome in cattle.