PERIPHERAL VASCULAR ALTERATIONS DURING EXPERIMENTAL HEART-FAILURE IN THE RAT - DO THEY EXIST

Structural changes of the peripheral vascular component as seen during hypertension and atherosclerosis have been suggested during heart failure but have never been reported. Therefore, we studied possible structural alterations in the peripheral vasculature in an experimental model of heart failure, induced by ligation of the left coronary artery in rats. Large conduit and resistance-type arteries were excised at 1, 3, 5, and 12 weeks after myocardial infarct induction (MI) or sham surgery. Vessel dimensions (medial cross-sectional area [CSA], internal and external diameters, and media-to-lumen ratios) as well as medial collagen and elastin volume fractions were measured by computerized morphometry. The hy droxyproline assay was used to determine collagen and elastin content biochemically. Ln separate groups of animals, peripheral tissue flows were measured by using radioactive microspheres 5 and 12 weeks after MI. To evaluate the effects of the degree of heart failure, the animals of the 12-week group (n=10) were subdivided into groups of moderate (<45% infarct size) and large (>45% infarct size) infarction. At all time points, body weights of sham-operated and MI rats were comparable. Lung weights of infarcted animals were increased proportionally to infarct size. No major changes in vessel dimensions were seen at the earlier time points. Twelve weeks after coronary artery ligation, significantly smaller CSAs were observed in several large conduit arteries such as the thoracic aorta, carotid artery, and superior mesenteric artery. These changes coincided with reductions in both internal and external diameters. In contrast, internal and external diameters of mesenteric and pulmonary resistance arteries were increased after 12 weeks of coronary artery ligation. The medial CSAs of these resistance arteries showed a tendency to increase. Collagen and elastin volume fractions of the large conduit arteries were comparable in both sham-operated and MI animals during the entire experimental period. This latter observation was confirmed by the results of the hydroxyproline assay, which showed no differences in collagen and elastin content. In general, no major changes could be observed in the absolute blood flow to peripheral tissues measured in resting conditions at 5 and 12 weeks after coronary artery ligation. The data indicate that MI induces diverse adaptive changes in the vascular system. Medial CSAs and internal and external diameters of large conduit arteries of MT-operated animals are smaller 12 weeks after infarction. These parameters show a tendency to increase in resistance-type arteries.