The purpose of this study was to analyse the mechanical properties of small coronary arteries from pigs with one-kidney, one-clip hypertension and normotensive control animals and to determine whether these could contribute to vascular structural changes observed in hypertension. Small coronary artery wall tension-internal circumference relationships were determined for coronary arteries mounted in a myograph and used to calculate incremental elastic modulus-stress relationships for arteries from normotensive and hypertensive pigs. Wall tension-internal circumference relationships were shifted to the left in arteries from hypertensive pigs, but the stress-strain and incremental elastic modulus-stress relationships were not influenced by the increased blood pressure load. These data indicate that small coronary arteries from hypertensive pigs are not less distensible than those from normotensive controls. Therefore the previously reported increased media thickness:lumen diameter ratios in coronary arteries in this model of hypertension are not a consequence of abnormal elastic properties and can be ascribed to a remodelling process.
1. Previous studies suggest that oxidatively modified low-density lipoproteins (oxLDL) contribute to the impairment of endothelium-dependent vasodilation in the large arteries of hypercholesterolaemic animals, whereas this may not be the case with regard to the impairment of coronary resistance vessels. For this reason, the effect of lipoproteins on coronary resistance arteries has been examined in this study. 2. The influence of lipoproteins on endothelium-dependent relaxation induced by acetylcholine (ACh) or sodium nitroprusside in PGF2 alpha-preconstricted rings from the large (1st order branch) and small coronary arteries (3rd order branch) and the aorta of New Zealand White rabbits, was investigated. 3. The sensitivity to ACh was greater in the large compared with the small diameter coronary arteries. 4. Endothelium-dependent relaxations were unaffected by native LDL. Oxidized LDL (0.5 and 1 mg protein mL-1) caused a reversible inhibition of relaxations in both preconstricted small and large coronary arteries which was overcome at high ACh concentrations. Similar inhibitions were found in the aorta. 5. Endothelium-independent relaxations elicited by sodium nitroprusside in the large and small coronary arteries were unaffected by the oxidized lipoproteins, indicating that soluble guanylate cyclase activity was unaltered. 6. It is concluded that inhibition of endothelium-dependent relaxation in the small diameter coronary arteries in hypercholesterolaemia may arise from products of oxidative modification of LDL present in the artery itself or released upstream from proximal lesions.
In isolated minipig coronary arteries the vasoconstrictor responses to acetylcholine and U46619, and the endothelium dependent, noradrenaline mediated relaxations, differ according to the branching order studied. These data provide further evidence for a regional heterogeneity of vascular responses in the porcine coronary vasculature.
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