Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2006
Publication Date: 11/1/2006
Citation: Klotz, J.L., Bush, L.P., Smith, D.L., Schafer, W.D., Smith, L.L., Vevoda, A.O., Craig, A.M., Arrington, B.C., Strickland, J.R. 2006. Assessment of vasoconstrictive potential of d-lysergic acid using an isolated bovine lateral saphenous vein bioassay. Journal of Animal Science. 84:3167-3175. Interpretive Summary: Important thermoregulatory responses to environmental temperature include vasoconstriction and vasodilatation. The use of venous tissue isolated from the left and right hind limbs exhibited contractile responses to norepinephrine in a dose-dependent manner, but did not differ between limbs. Also, the overnight storage of venous tissue in a modified Krebs-Henseleit buffer at 2 to 8'C did not affect tissue responsiveness to norepinephrine. Thus, permitting future experiments that can utilize tissue from one leg and utilize tissue from a second leg following an event, such as exposure to endophyte-infected tall fescue. Additionally, data presented here show that lysergic acid is a weak vasoconstrictor and then only at supraphysiological levels as assessed by this blood vessel model. Apparently unlike the ergotamine and ergovaline, lysergic acid does not appear to bind tightly to the tissues, thereby reducing the potential for bioaccumulation. Thus, as vasoconstriction is a major component of fescue toxicosis, these data indicate that lysergic acid may play a minor role in the expression vascular complications associated with fescue toxicosis. However, further research is needed to fully address other direct or indirect effects that lysergic acid may contribute to fescue toxicosis.
Technical Abstract: Vasoconstriction has been associated with several symptoms of fescue toxicosis thought to be alkaloid induced. Lysergic acid, an ergot alkaloid, has been proposed as a toxic component of endophyte-infected tall fescue. The objective of this study was to examine the vasoconstrictive potential of D-lysergic acid (n = 12) using a bovine lateral (cranial branch) saphenous vein bioassay. Prior to testing lysergic acid, validation of the bovine lateral saphenous vein bioassay for use with a multi-myograph apparatus was conducted using dose-response to norepinephrine (n = 7) in order to evaluate effects of limb of origin (right versus left) and overnight storage on vessel contractile response. Segments (2-3 cm) of the cranial branch of lateral saphenous vein were collected from healthy mixed breed cattle at local abattoirs. Tissue was placed in modified Krebs-Henseleit oxygenated-buffer and kept on ice or stored at 2–8'C until used. Veins were trimmed of excess fat and connective tissue, sliced into 2-3 mm sections and suspended in a myograph chamber containing 5 mL of oxygenated Krebs-Henseleit buffer (95% O2/5% CO2; pH = 7.4; 37'C). Tissue was allowed to equilibrate at 1 g of tension for 1.5 h prior to initiation of treatment additions. Increasing doses of norepinephrine (1x10-8 to 5x10-4 M) or lysergic acid (1x10-11 to 1x10-4 M) were administered every 15 min following buffer replacement. Data were normalized as a percent of contractile response induced by a maximal dose of norepinephrine administered. Veins from both left and right limbs demonstrated contractions in a dose-dependent manner (P < 0.01), but did not differ between limbs. There were no differences in dose-response to norepinephrine between tissue tested the day of dissection and tissue exposed 24 h later. Exposure of vein segments to increasing concentrations of lysergic acid did not result in a measurable contractile response until 1x10-5 M concentration. The addition of 1x10-4 M lysergic acid resulted in a contractile response of 15.6 ' 2.3 % of the norepinephrine (1x10-4 M) response. These data indicate that only supraphysiological concentrations of lysergic acid results in vasoconstriction. If physiological systems in the animal are affected similarly, lysergic acid may only play a minor role in the manifestation of fescue toxicosis.