Neurogenic dilatation and constriction of rat superior mesenteric artery in vitro: mechanisms and mediators

Canadian Journal of Physiology and Pharmacology
M S Kannan, A E Seip

Abstract

In the rat superior mesenteric arteries, the mechanical responses to perivascular nerve stimulation were characterized. The predominant response was contraction mediated by the release of norepinephrine, acting postjunctionally on alpha 1-adrenoceptors. These frequency-dependent contractions were unaffected by the alpha 2-selective adrenoceptor antagonist yohimbine, but were markedly attenuated by clonidine, the alpha 2-selective adrenoceptor agonist. In the presence of prazosin, the alpha 1-selective antagonist, a significant component of the nerve-mediated contraction was still present. At the concentrations used, prazosin, yohimbine, as well as clonidine acted as competitive antagonists of response to exogenous norepinephrine. This differential inhibition of norepinephrine- and nerve-mediated responses suggested the presence of distinct postjunctional adrenoceptors. The effects of clonidine and yohimbine are interpreted to arise from prejunctional modulation of norepinephrine release. In 30 of the 100 vessels studied, there was spontaneous myogenic tone. In these arteries, field stimulation caused frequency- and voltage-dependent relaxations. These responses were neural in origin, dependent on sympathetic nerve activity, but...Continue Reading

Citations

Nov 1, 1995·Clinical and Experimental Pharmacology & Physiology·J L Morris
May 30, 2003·Pharmacological Reviews·Noboru Toda, Tomio Okamura

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