Comparative effects of diuretics and atrial peptide in chronic caval dogs

Anesthetized chronic caval dogs with ascites were given atrial natriuretic peptide (ANF) at 75 ng.kg-1.min-1 iv and were characterized as to natriuretic response [n = 21; urinary excretion rate of Na (UNaV): 28-362 mu eq/min] or lack of response (n = 14; UNaV: 0-10 mu eq/min). Sixteen normal dogs showed an increment in UNaV between 38 and 288 mu eq/min following the same dose of ANF. Both caval "responders" and "nonresponders" were equivalent with regard to pre- and post-ANF hemodynamics and renal function. When various diuretic agents (glucagon, acetazolamide, furosemide, thiazide, amiloride) were administered, equivalent natriuretic responses were obtained between both groups of caval dogs and the controls. An acute saline load (7% body wt), however, produced a greater natriuresis in controls than in caval dogs, but in this latter group the response was similar in responders and nonresponders. When six caval dogs each were initially pretreated with either amiloride or ANF, and then treated with a second agent, an additive natriuretic effect was obtained. These results suggest that tubular resistance to diuretics in caval dogs is unique to ANF, and this peptide appears to act at an additional Na transport site separate from amiloride-inhibitable channels.