MESENTERIC SMALL ARTERY CHANGES AFTER VASOCONSTRICTOR INFUSION IN YOUNG-RATS

We evaluated whether chronic alpha1-adrenergic stimulation, angiotensi n II (AII), or increased blood pressure (BP) alters resistance arteria l structure and function. Structural parameters and wall tension were recorded in mesenteric small arteries (MrA) isolated from 6-week-old n ormotensive Wistar Kyoto rats that had been infused for 4 days with sa line (WKY), 2 mg/kg/day phenylephrine (WKY + PHE), or 0.3 mg/kg/day AI I (WKY + AII) and from saline-infused spontaneously hypertensive rats (SHR). During the experimental period, systolic BP (SBP) did not chang e in WKY but increased in WKY + PHE, WKY + AII, and SHR. Relative card iac mass did not differ between SHR and WKY, but was increased in WKY + PHE and WKY + AII. Stiffness and optimal lumen diameter of MrA did n ot differ between WKY and SHR and were not altered in WKY + PHE or WKY + AII. Maximal contractile responses and sensitivities for vasoconstr ictors and calcium in vessels of WKY + All and SHR did not differ from those in WKY. In vessels of WKY + PHE, maximal responses to vasoconst rictors and sensitivities for norepinephrine (NE) and PHE were reduced . Relaxing responses to isoproterenol (ISO) and Na-nitroprusside did n ot differ between SHR and WKY and were not altered in WKY + PHE and WK Y + AII. Those to acetylcholine (ACh) were reduced in WKY + PHE. Media cross-sectional area and media thickness were significantly larger in WKY + AII and SHR as compared with WKY but were not altered in WKY PHE. These data indicate that in young rats AII leads to small artery hypertrophy and that neither increased BP nor increased vasoconstricti on appear to be involved therein. Chronic alpha1-adrenergic stimulatio n, on the other hand, did not modify small artery structure but result ed in nonselective reduction of arterial smooth muscle contractile re- activity.