Regional hemodynamics after chronic nitric oxide inhibition in spontaneously hypertensive rats

Background: Inhibition of nitric oxide (NO) synthase by L-arginine analogs is associated with elevation of blood pressure in rats. Because endothelium -dependent vasomotion in different vascular beds is not homogenous, the aim of this study was to characterize and compare regional hemodynamic respons es in carotid, femoral, and renal vascular beds after chronic NO inhibition in spontaneously hypertensive rats. The possible role of circulating endot helin and renin angiotensin systems in mediating the effects of chronic NO inhibition was also studied. Methods: Systemic and regional hemodynamics, l eft ventricular mass, plasma renin activity, and plasma endothelin-l were d etermined in control and N-omega-nitro-L-arginine methyl ester (L-NAME)-tre ated (10 mg/kg/day, 4 weeks) spontaneously hypertensive rats. Results: L-NA ME treatment increased arterial pressure and total peripheral and regional vascular resistance and decreased cardiac output, stroke volume, and region al blood flow. An in-crease in blood flow ratio and a decrease in vascular resistance ratio between carotid and renal as well as femoral and renal vas cular beds in rats treated with L-NAME was found. Blood flow and vascular r esistance ratios between femoral and carotid vascular beds remained unchang ed. L-NAME increased plasma renin activity and left ventricular weight/body weight ratio, whereas plasma endothelin-l was not modified. Conclusions: T he results of this study showed that the renal circulation seemed to be mor e sensitive to the effects of chronic NO inhibition than carotid and femora l vascular beds. Simultaneous activation of the renin angiotensin system ma y further potentiate cardiovascular effects of chronic NO inhibition. No ev idence that circulating endothelin-l plays a role in this model of hyperten sion was found. KEY INDEXING TERMS: Nitric oxide; Regional hemodynamics; Pl asma renin activity; Endothelin; Spontaneously hypertensive rats.