Vascular and myocardial protective effects of converting enzyme inhibition in experimental heart failure

Systemic vasoconstriction due to stimulation of the sympathetic and renin-angiotensin-aldosterone systems is a hallmark of heart failure and this is accompanied by impaired endothelium-dependent relaxations at the level of large arteries. This study investigated, in a rat model of heart failure, whether such an endothelial dysfunction also exists at the level of the resistance artery, and whether this is associated with morphologic changes, as well as the effects of chronic treatment with the angiotensin-converting enzyme inhibitor perindopril (2 mg/kg/day). After 12 months, arterial pressure, left ventricular (LV) end diastolic pressure (LVEDP), and LV dP/dt were measured in anesthetized rats. Responses to acetylcholine and nitroprusside were determined in isolated and perfused mesenteric artery segments (diameter: 280 +/- 15 microns). After fixation, vessel diameter, media cross-sectional area, and media collagen and elastin densities were measured by image analysis. After 12 months, untreated rats showed signs of heart failure, i.e., reduced LV dP/dt, and increased LVEDP, heart weight/body weight, LV cavity circumference, and myocardial collagen density. In mesenteric vessels the endothelium-dependent vasodilator response to acetylcholine was impaired, whereas the response to the nitric oxide donor nitroprusside was unaffected. Heart failure did not affect vascular morphological parameters. Perindopril decreased blood pressure and LVEDP without any modification of LV dP/dt, and prevented cardiac remodeling. At the vascular level, perindopril improved the response to acetylcholine and reduced media cross-sectional area and collagen density without affecting internal vessel diameter or elastin density. Thus, heart failure decreases endothelium-dependent vasodilator response to acetylcholine without modification of vessel structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of endothelium in the mechanical response of the carotid arterial wall to calcium blockade in spontaneously hypertensive and Wistar-Kyoto rats

OBJECTIVES

Calcium blockade has been reported to inhibit the contraction of the vascular smooth muscle and the liberation of vasoactive substances by endothelial cells. We tested the effects of calcium blockade on the mechanical properties of the carotid artery in normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) in the presence and in the absence of endothelium.

METHODS

The pressure-volume relationships of isolated carotid arteries were recorded in situ in SHR (n = 20) and WKY rats (n = 20) before and after calcium blockade by local incubation with clentiazem.

RESULTS

With intact endothelium, calcium blockade induced a significant shift in the pressure-volume curve in both strains, volume being significantly higher after calcium blockade than under control conditions. In WKY rats the carotid mechanical properties were similar after calcium blockade and after abolition of the smooth muscle tone by potassium cyanide (KCN) poisoning. In SHR the carotid compliance measured after incubation with clentiazem was significantly lower than that measured after KCN poisoning. Removal of the endothelium induced a significant shift in the pressure-volume curve towards the volume axis in both strains, and an increase in carotid compliance. Local incubation with clentiazem or KCN did not induce further modifications of the pressure-volume relationship either in WKY rats or in SHR. Furthermore, in SHR and WKY rat carotid arteries, the pressure-volume relationship and the compliance measured after incubation with clentiazem were identical in the presence and in the absence of endothelium.

CONCLUSIONS

In WKY rat and SHR carotid arteries, acute calcium blockade increases the arterial compliance independently of the endothelium integrity. Furthermore, part of the compliance enhancement induced by the calcium antagonist could be related to an antagonizing mechanism of the production of endothelial constricting factor or factors.