Submitted to: Joint Meeting of the ADSA, AMSA, ASAS and PSA
Publication Type: Abstract Only
Publication Acceptance Date: March 2, 2010
Publication Date: July 11, 2010
Citation: Klotz, J.L., Strickland, J.R., Bush, L.P., Kirch, B.H., Brown, K.R. 2010. Antagonism of 5-hydroxytryptamine2A Receptor Results in Decreased Contractile Response of Bovine Lateral Saphenous Vein to Tall Fescue Alkaloids. J. Anim. Sci. Vol. 88, E-Suppl. 2/J. Dairy Sci. Vol. 93, E-Suppl. 1/Poult. Sci. Vol. 89, E-Suppl. 1. pg 55. Technical Abstract: Pharmacologic profiling of 5-hydroxytryptamine (5HT) receptors of bovine lateral saphenous vein has shown that cattle grazing endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum) have altered responses to ergovaline (ERV), 5HT, 5HT2A and 5HT7 agonists. To determine if 5HT receptor binding of tall fescue alkaloids is affected by grazing endophyte-free (EF), wild type (WT), or novel endophyte-infected (NE) tall fescue, contractile responses of lateral saphenous veins biopsied from cattle grazing these different fescue-endophyte combinations were evaluated in presence or absence of antagonists for 5HT2A (ketanserin; KET) or 5HT7 (SB-269970; SB). Biopsies were conducted over 2 years on 35 mixed breed steers (361.5 ' 6.3 kg) grazing KY31 (WT; n=12), EF (n=12), MAXQ (NE AR542; n=6) or KYFA9301 (NE AR584; n=5) pasture treatments (3 ha) between 84-98 d (Yr 1) or 108-124 d (Yr 2). Segments (2-3 cm) of vein were surgically biopsied, sliced into 2-3 mm cross-sections, and suspended in a myograph chamber containing 5 mL of oxygenated Krebs-Henseleit buffer (95% O2/5% CO2; pH = 7.4; 37'C). Veins were exposed to increasing concentrations of 5HT, ERV, and ERV+1x10-5 M KET, or +1x10-6 M SB in Yr 1. In Yr 2, ergotamine (ERT) and ergocornine (ERO) were evaluated in presence or absence of 10-5 M KET. Data were normalized to a reference addition of 1x10-4 M norepinephrine and analyzed as a CRD factorial with steer as experimental unit. In Yr 1, contractile response to 5HT and ERV were lowest in WT KY31 pastures (P<0.05) and the presence of KET greatly reduced the response to ERV in all pastures (P<0.05). The presence of SB did not alter contractile response to ERV. In Yr 2, there was no difference in response to ERO or ERT across pastures, but KET again reduced the contractile response (P<0.05). The 5HT2A receptor is involved in alkaloid-induced vascular contraction and alkaloid binding may be affected by exposure to different endophyte-fescue combinations.