Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 3/9/2008
Publication Date: 7/7/2008
Citation: Klotz, J.L., Brown, K.R., Xue, Y., Matthews, J.C., Boling, J.A., Bush, L.P., Strickland, J.R. 2008. Grazing Endophyte-Infected Tall Fescue Alters Serotonin Receptor-Induced Contractility of Bovine Lateral Saphenous Veins. J. Anim. Sci. Vol. 86. p 102.
Technical Abstract: Concurrent with grazing of endophyte-infected tall fescue is the consumption of toxic alkaloids that negatively affect cardiovascular function and result in fescue toxicosis. Vascular effects of ergopeptine alkaloids are mediated by stimulation of various biogenic amine receptors yet to be fully characterized. The objective was to evaluate the effect of grazing 2 levels of toxic endophyte-infected tall fescue on the vasoconstrictive activities of (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI), BW 723C86 (BW), CGS-12066A (CGS), and 5-carboxamidotryptamine hemiethanolate maleate (5CT), agonists for 5-hydroxytryptamine (HT)2A, 2B, 5-HT1B and 5-HT7 receptors, respectively. Segments (2-3 cm) of the cranial branch of the lateral saphenous vein were collected at time of slaughter from steers following a 114 to 127-d grazing period of either a low endophyte-infected (LE) mixed grass pasture (10% infection; n=8; BW=327±9 kg) or a high endophyte-infected (HE) tall fescue pasture (92% infection; n=8; BW=306±9 kg). Veins were 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) and allowed to equilibrate at 1 g of tension for 90 min. Increasing concentrations of DOI, BW, CGS, and 5CT were administered every 15 min. Data were normalized (%) to contractile response induced by a reference dose of norepinephrine (1x10-4 M) and data for each treatment were analyzed for effects of concentration and endophyte level. Maximal contractile intensities achieved with DOI were decreased 35% (P < 0.05) in steers grazing HE pastures, whereas those achieved with 5CT were increased 37% (P < 0.05). The contractile response to CGS did not differ between pasture groups and there was an absence of contractile response to BW in both groups. Grazing HE pastures alters vascular responses which may be mediated through modified serotonin receptor activities.