FUROSEMIDE-INDUCED NATRIURESIS IS AUGMENTED BY ULTRA-LOW-DOSE CAPTOPRIL BUT NOT BY STANDARD DOSES OF CAPTOPRIL IN CHRONIC HEART-FAILURE

Background. Ten chronic heart failure patients were studied on three occasions in randomized double-blind fashion to compare the acute hemodynamic, neurohormonal, and renal sodium-handling responses to 1 mg captopril versus 25 mg captopril, both in the absence of loop diuretic therapy and during furosemide-stimulated natriuresis. Methods and Results. Compared with placebo, 1 mg captopril caused nonsignificant decreases in mean arterial pressure and circulating angiotensin II level and had no effect on glomerular filtration rate as determined by Cr-51-EDTA elimination. Captopril (25 mg) produced marked suppression of serum angiotensin II with or without oral furosemide (both p<0.002), a marked decrease in mean arterial pressure (p<0.0001) that was accentuated by furosemide (p<0.00001), and a decrease in glomerular filtration rate (p=0.0007). No difference from placebo in renal sodium excretion was noted with either 1 or 25 mg captopril in the absence of furosemide. In contrast, while 25 mg captopril caused slight attenuation of the natriuretic response to furosemide, 1 mg captopril significantly enhanced furosemide-induced natriuresis (p<0.05). No correlation was found in our patients between the natriuretic effect of furosemide and either absolute mean arterial pressure or change in mean arterial pressure during the furosemide phase of each study session. This suggests that blood pressure is not the important factor mediating the divergent renal responses to furosemide of the two captopril dosage regimens. Conclusions. We propose that in the face of furosemide-induced postglomerular vasodilatation in chronic heart failure, captopril at a starting dose of 1 mg (but not 25 mg) preserves enough circulating angiotensin II to maintain efferent arteriolar tone and thus glomerular filtration, while offsetting the antinatriuretic renal tubular effects of angiotensin II.