PP.11.11] ADAPTIVE VASOACTIVE PROPERTIES OF THORACIC AORTA IN YOUNG NORMOTENSIVE AND SPONTANEOUSLY HYPERTENSIVE RATS

Abstract

Objective: Through its elasticity, the aorta plays an important role in the control of blood pressure. The aortic stiffness is associated with functional changes so the early determination of vasoactive properties could be one of the detectable manifestations of pathological changes in the hypertension. The aim was to compare the vasoactive responses of thoracic aorta (TA, elastic vessel type) and mesenteric artery (MA, muscular vessel type) in young normotensive rats (Wistar) and spontaneously hypertensive rats (SHR). Design and method: In acute experiment 4-weeks old Wistar rats and SHR were used. In chronic experiment the control rats and rats treated with NG-nitro-L-arginine metylester (L-NAME, 50 mg/kg/day) of both strains were used to evaluate the effect of nitric oxide (NO) deficiency. Systolic blood pressure (sBP) was measures by plethysmographic method. The vasoactivity of TA and MA was evaluated by changes in isometric tension. Results: In 4-weeks SHR the sBP was not increased in spite of cardiac hypertrophy compared to Wistar rats. Vasoconstrictor responses induced by exogenous noradrenaline (NA) were decreased in TA in SHR compared to Wistar, in MA they were comparable between both strains. Endothelium-dependent vasorelaxation of TA was preserved in both strains, however, NO component was increased in SHR. The L-NAME administration induced the stabile hypertension without cardiac hypertrophy in Wistar and transient sBP increase associated with aggravated cardiac hypertrophy. NA vasoconstrictor responses were increased in MA and decreased in TA in normotensive rats in L-NAME group. In SHR the chronic NO deficiency led to the increase of contractions in TA and to the collapse of contractile apparatus in MA. After L-NAME administration the endothelium-dependent vasorelaxation of TA was inhibited in normotensive rats, however, it was unchanged in SHR. Conclusions: Young pre-hypertensive SHR dispose of inherent predisposition involving: a) an unimpaired endothelium-dependent vasorelaxation with increased NO component; b) heterogeneity of contractility of elastic and muscular type of arteries. TA, by contrast to MA, revealed the adaptive contractile responses in both strains, which was supplemented by activation of vasorelaxant compensatory mechanisms in SHR.