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Cellular changes in mesenteric arteries and veins after acute perfusions of angiotensin II and vasoactive amines.

Cross-sections of rat mesenteric vessels were examined histologically after short-term perfusions of angiotensin II (AII), norepinephrine (NE), 5-hydroxytryptamine (5-HT), and histamine. Mesenteric veins (300-400 micron) and muscular venules (50-100 micron) exhibited dose-dependent constrictor responses to AII, but not to NE. Arterioles of comparable size (50-100 micron) did not constrict at low doses of AII or NE, but responded when higher pressor concentrations of each agonist were perfused. At equipressor doses, constriction of mesenteric arterioles was greater following NE when compared with AII. Short perfusions of 5-HT resulted in mild venoconstriction, while histamine induced dilation of the muscular venules. Ultrastructurally, vascular damage in response to AII was minimal and confined to the formation of small vacuoles in the endothelial cytoplasm. Endothelial integrity was preserved and no autonomous endothelial contraction was observed. Vacuolation induced by NE was far more extensive and particularly evident in arteries and arterioles.