60% of chronic caval dogs with ascites did not respond to atrial natriuretic peptide (ANP) (75 ng.kg-1.min-1) with a natriuresis (TIVC-NR; delta UNaV = 2 +/- 0.8 mu eq/min) whereas the remaining 40% responded normally (TIVC-R; delta UNaV = 216 +/- 50 mu eq/min). Since proximal tubule neutral endopeptidase 24:11 (NEP) destroys most of intrarenal luminal ANP and kinins, we attempted to convert TIVC-NR into TIVC-R by providing NEP inhibition with SQ 28603 at 30 mg/kg. This potent and specific NEP inhibitor produced a natriuresis when administered alone to nine TIVC-NR dogs (delta UNaV = 67 +/- 2 mu eq/min) and permitted a natriuresis in the presence of ANP (delta UNaV = 97 +/- 18 mu eq/min). A natriuretic response to ANP could also be induced in TIVC-NR dogs by providing renal arterial bradykinin or intravenous captopril, a kininase inhibitor. Urodilatin, a natriuretic peptide not destroyed by intrarenal NEP was without effect in TIVC-NR dogs but increased UNaV when given to TIVC-R and normal dogs. Providing bradykinin to TIVC-NR now permitted an increment in delta UNaV (62 mu eq/min) when urodilatin was reinfused. TIVC-R dogs could be converted into TIVC-NR by pretreating with a specific bradykinin antagonist before infusing ANP. We conclude that TIVC-NR dogs are deficient in intrarenal kinins but are converted to responding dogs after NEP inhibition because of increased kinin delivery to the inner medullary collecting duct.
L Legault, P Cernacek, M Levy, E Maher, D Farber