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Vasodilator responses of rat mesenteric vessels to trace amines mediated via nitric oxide

The vascular effects of trace amines in the mesenteric arterial bed have not been fully established. We hypothesize that the vascular responses are mediated by trace amine‐associated receptors (TAARs). Vasodilator responses to the trace amines, tyramine, β‐phenylethylamine (PEA), tryptamine and octopamine were investigated in vitro in rat perfused mesenteric arterial beds pre‐constricted with phenylephrine. Trace amines induced concentration‐dependent falls in perfusion pressure in mesenteric arterial beds. Ritanserin was perfused during tryptamine studies, to eliminate a predominant 5‐HT2A receptor‐mediated vasoconstriction. The rank potency order of the trace amines was tyramine > PEA > tryptamine > octopamine which corresponds with that for the rat TAAR1 expressed in HEK293 cells (Bunzow et al. 2001), suggesting that the vasorelaxation response to trace amines in the perfused mesenteric bed could be mediated by rat TAAR1. The nitric oxide (NO) synthase inhibitor L‐NAME, abolished the vasodilatations by tyramine, PEA and tryptamine, suggesting that the vasorelaxations are mediated via NO.