Endothelium-dependent mechanical properties of the carotid artery in WKY and SHR. Role of angiotensin converting enzyme inhibition

Abstract

An experimental model of in situ isolated carotid arteries has been used to evaluate the static mechanical properties of the arterial wall in 12-week-old Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The effects of endothelium removal and of local incubation with the converting enzyme inhibitor lisinopril (ICI Pharma 209000) on the carotid compliance (CC) were compared with the effects of total abolition of the vascular smooth muscle tone by potassium cyanide. CC measured fro pressures ranging from 50 to 175 mm Hg had maximal values (0.22 ± 0.07 μl/mm Hg and 0.13 ± 0.03 μl/mm Hg, respectively, for WKY and SHR, p < 0.001) for pressure values close to the operating pressures in both groups. Maximal values of CC were increased by 35% and 45% in WKY and SHR, respectively, after potassium cyanide poisoning (p > 0.01). The endothelium removal induced a significant increase in CC compared with their control values (+37%, p < 0.01, and +25%, 0 < 0.01, respectively, in WKY and SHR). CC measured after endothelium removal did not significantly differ from its values measured after potassium cyanide poisoning in normotensive animals. In contrast, in hypertensive animals, CC was significantly lower after endothelium removal than after potassium cyanide poisoning (p < 0.01). In the presence of intact indothelium, local incubation with converting enzyme inhibitor increased CC by 23% (p < 0.05) in WKY rats and by 14% (p < 0.01) in SHR. In contrast, after endothelium removal, converting enzyme inhibitors did not significantly increase further CC in either strain. The present results suggests that the mechanical properties of the wall of the carotid artery are endothelium dependent. The relative constricting role of the endothelium seems to be more predominant in normotensive than in genetically hypertensive rats. The vascular converting enzyme seems to be involved in the endothelium dependent wall properties bacause endothelium removal and local application of converting enzyme inhibitors had similar effects on CC.