Altered contractile responses of arteries from spontaneously hypertensive rat: The role of endogenous mediators and membrane depolarization

Abstract

AimsThe goal of our study was to reveal the important mechanism(s) responsible for the enhanced contractility of isolated arteries from animals suffering genetic hypertension. Main methodsContractile force of endothelium-denuded arteries, modulated by various interventions, was measured by wire myography. Key findingsSpontaneously hypertensive rat (SHR) and Wistar-Kyoto rat (WKY) arteries were stimulated by norepinephrine, increased extracellular K+ or tyramine. Strain difference was not observed in the contraction elicited by exogenous norepinephrine but SHR arteries responded more to tyramine (causing endogenous norepinephrine release from neuronal varicosities). K+-induced contraction was enhanced in SHR arteries, with no involvement of endogenous catecholamines. The α-adrenoceptor blockade lowered tyramine-induced contraction more in SHR arteries; similar effect was achieved by guanethidine-induced sympathectomy. Partial depolarization of WKY arteries by 20mM K+ enhanced its contraction to SHR level. The blockade of β-adrenoceptors by propranolol or selective β2-antagonist ICI-118,551 induced contraction of SHR endothelium-denuded arteries but was without significant effects on WKY arteries unless they were stimulated with K+. Both tyramine-induced and propranolol-induced contractions were attenuated by flupirtine and abolished by nifedipine. SignificanceThe differences of SHR and WKY arteries were not related to vascular expression of α- and β-adrenoceptors or G-proteins. Enhanced contractility of SHR arteries is related to both increased presence of endogenous norepinephrine in vascular wall and also to altered vascular smooth muscle membrane potential.