ANGIOTENSIN-II INDUCES MEDIA HYPERTROPHY AND HYPERREACTIVITY MESENTERIC BUT NOT EPIGASTRIC SMALL ARTERIES OF THE RAT

We examined effects of a 2-week infusion of angiotensin II (AII, 250 n g.kg(-1).min(-1)) on properties of mesenteric resistance arteries (MrA ) and superior epigastric arteries (SEA) of male Wistar rats. Histoche mistry and pharmacological tools showed that MrA are densely innervate d, whereas SEA are only sparsely innervated. AII infusion resulted in a significant elevation in mean arterial pressure and in plasma AII an d noradrenaline levels. Organ chamber studies and morphometry were use d to determine arterial contractile reactivity and structure. After AI I infusion, in MrA (i) maximal contractile responses to 125 mM K+, nor adrenaline, serotonin and adrenergic nerve stimulation were significan tly increased, without modification of the sensitivity to these stimul i and (ii) a significant increase in media cross-sectional area and me dia thickness was observed without alterations in lumen diameter. The observed increase in vascular reactivity could fully be attributed to the observed increase in wall mass since no alterations in maximal act ive wall stress were noted. In SEA, no significant changes in responsi veness to vasoconstrictor stimuli or in wall structure were observed. These findings suggest that perivascular nerves are involved in the hy pertrophy and subsequent hyperreactivity of small arteries in rats exp osed for 2 weeks to a low dose of AII.