Submitted to: Joint Meeting of the ADSA, AMSA, ASAS and PSA
Publication Type: Abstract Only
Publication Acceptance Date: March 8, 2011
Publication Date: July 11, 2011
Citation: Klotz, J.L., Aiken, G.E., Foote, A.P., Bush, L.P., Brown, K.R., Goff, B.M., Strickland, J.R. 2011. Contractile response of bovine lateral saphenous vein to ergovaline serotonin2A a2A- and a2C-adrenergic receptor agonists relative to time off endophyte-infected tall fescue. Joint Meeting of the ADSA, AMSA, ASAS and PSA. 89(E-Suppl. 1):50. Technical Abstract: Previous research has demonstrated differences in contractile responses to ergot alkaloids, serotonin (5HT), and adrenergic agonists by lateral saphenous veins collected from cattle that grazed either endophyte (Neotyphodium coenophialum)-infected or endophyte-free tall fescue (Lolium arundinaceum), possibly influenced by an altered vascular receptor profile. To aid in understanding of how cattle recover after exposure to toxic tall fescue, lateral saphenous vein biopsies were conducted on 24 predominantly Angus steers (357 '3 kg) at 0 (n=6), 7 (n=6), 14 (n=5), and 28 d (n=4) after removal from grazing KY31 tall fescue pasture (3.0 ha) for 126 d. Off-pasture, animals were housed in a dry lot and fed a corn silage and soybean hull mixed diet. Biopsied segments (2-3 cm) of vein were sliced into 2-3 mm cross-sections and suspended in a myograph chambers containing 5 mL of oxygenated Krebs-Henseleit buffer (95% O2/5% CO2; pH = 7.4; 37'C). Veins were exposed to increasing concentrations of ergovaline (ERV), TCB2 (5HT2A agonist), guanfacine HCl (GF; '2A-adrenergic agonist), and (R)-(+)-m-nitrobiphenyline oxalate (NBP; '2C-adrenergic agonist). Data were normalized to a reference addition of 1x10-4 M norepinephrine (NE) and analyzed as a CRD for main effects of d off pasture, concentration of agonist, and d off pasture ' concentration with steer as experimental unit using mixed models of SAS. Main effects of agonist concentration and d (d 7 and 14 were greater than d 0 and 28) were significant (P<0.01), but d off pasture ' concentration was not significant (P>0.1) for all 4 compounds tested. ERV and TCB2 had the greatest maximal responses and 2 adrenergic agonists elicited relatively smaller responses. Response to increasing concentrations GF was the least and varied most across d. NBP, the '2C agonist, was the more vasoactive adrenergic agonist. The effect of animal recovery during the 28-d off of tall fescue did not affect the relative response through changes in the biogenic amine receptor profile as evaluated pharmacologically in the bovine saphenous vein.