ENALAPRIL BLUNTS THE ANTINATRIURETIC EFFECT OF CIRCULATING NORADRENALINE IN MAN

Objective: The present study examines the effect of angiotensin conver ting enzyme inhibition on the renal haemodynamic and sodium excretory responses to noradrenaline in man. Design: We studied the effects of i ntravenous noradrenaline (0.075 mug/kg per min) and enalapril pretreat ment (5 mg/day for 5 days), alone and in combination, on urinary sodiu m excretion, effective renal plasma flow, glomerular filtration rate a nd segmental tubular function in nine normal subjects. Methods: The su bjects were studied during maximal water diuresis. The clearance of in ulin and of para-aminohippurate were used to estimate the glomerular f iltration rate and effective renal plasma flow, respectively. Segmenta l tubule handling of sodium was assessed by the lithium clearance meth od. Results: Noradrenaline alone decreased urinary sodium excretion (P <0.01) and the effective renal plasma flow (P<0.01) without altering t he glomerular filtration rate. Enalapril pretreatment significantly at tenuated this fall in sodium excretion (P<0.05) and effective renal pl asma flow (P<0.05), and had a similar attenuating effect on the noradr enaline-induced decrease in the fractional excretion of lithium. The p ressor response to noradrenaline infusion was not, however, influenced by the enalapril pretreatment. Conclusions: Enalapril blunts the rena l vasoconstrictive effect and the antinatriuretic effect of noradrenal ine in man. Our results indicate that there is an important interactio n between the sympathetic nervous system and the renin-angiotensin sys tem in the kidneys in man.