|BUSSARD, JESSICA - University Of Kentucky|
|FOOTE, ANDREW - University Of Kentucky|
|HARMON, DAVID - University Of Kentucky|
|GOFF, BEN - University Of Kentucky|
Submitted to: Joint Meeting of the ADSA, AMSA, ASAS and PSA
Publication Type: Abstract Only
Publication Acceptance Date: 3/6/2012
Publication Date: 7/15/2012
Citation: Klotz, J.L., Bussard, J.R., Aiken, G.E., Foote, A.P., Harmon, D.L., Brown, K.R., Goff, B.M., Strickland, J.R. 2012. Lateral saphenous vein responses to serotonergic and a-adrenergic receptor agonists increase with time off endophyte-infected tall fescue. J. Anim. Sci. Vol. 90, Suppl. 3:34.
Technical Abstract: Previous research has indicated that serotonergic and a-adrenergic receptors in peripheral vasculature are affected by exposure of cattle grazing toxic endophyte-infected (E+) tall fescue (TF; Lolium arundinaceum). This study was conducted to investigate changes in vascular contractile response over time relative to removal from an E+ TF pasture after an 88-d grazing period. Lateral saphenous veins were biopsied from 24 Angus-cross steers (361±4 kg) at 0-, 21-, 42-, and 63-d off of TF pasture (n=6 per time point) and 6 steers (370±18 kg) off of bermudagrass (BG) pasture on d-0 and d-63 (n=3 per time point). Off pasture, steers were housed in a dry lot and fed a corn silage diet. Biopsied vessels were cleaned and incubated in a multimyograph and exposed to increasing concentrations (5x10-8 to 1x10-4 M)of TCB-2 (TCB; 5HT2A agonist), guanfacine (GF; a2A-adrenergic agonist), and (R)-(+)-m-nitrobiphenyline oxalate (NBP; a2C-adrenergic agonist). Data were normalized to a reference addition of 1x10-4 M norepinephrine and analyzed as a CRD using mixed models of SAS for main effects of d off pasture, agonist concentration, the interaction, and comparison of TF to BG veins at d-0 and d-63 included a pasture effect. Steer was the experimental unit. Increasing concentrations of 3 agonists incubated with TF veins were significant for agonist (P<0.01) and d off pasture (P<0.01), but only TCB was significant for d off pasture × concentration interaction (P<0.01). Vasoactivity to agonists was reduced when steers were initially removed from E+ TF pasture. Contractile response at d-63 was greatest (P<0.05) for GF, NBP, and TCB and d-42 TCB response was greater (P<0.05) than d-21 or d-0 (which did not differ). Contractile responses to NBP at d 0 were greater in BG veins (P<0.01) than TF and tended to be greater (P=0.07) for GF and TCB, but none were different at d 63. These data demonstrate changes in peripheral vasoactivity occur beyond 1 month off pasture and 5HT2A receptors appear to be more dramatically affected in the lateral saphenous vein by grazing E+ TF pasture than adrenergic receptors.