SODIUM LOADS ENHANCE THE NATRIURETIC RESPONSES TO ATRIAL NATRIURETIC PEPTIDE AND NEUTRAL ENDOPEPTIDASE INHIBITORS IN CONSCIOUS CYNOMOLGUS MONKEYS

1. The effects of sodium supplements on the renal responses to human atrial natriuretic peptide (hANP 99–126) and to the selective inhibitors of neutral endopeptidase 3.4.24.11 (NEP) SQ 28 603 and candoxatrilat were determined in conscious monkeys. 2. When the monkeys’ diet was changed from 0.55% sodium to 1.1% sodium, the natriuretic response to 100 μmol/kg intravenous of SQ 28603 increased from 665 ± 64 to 1015 ± 224 μEq/3h. An acute oral load of 25 mEq sodium significantly increased the natriuresis stimulated by 300 pmol/kg, P.o., of SQ 28603 from 700 ± 332 μEq/3h in normal monkeys to 2437 ± 841 μEq/3h. Therefore, the non-human primate model was appropriate for investigating the effects of sodium loads on the urinary ANP and cGMP responses to exogenous ANP in the presence and absence of NEP inhibitors. 3. Graded intravenous infusions of saline increased basal urine volume and excretion of sodium and ANP. Salt supplements enhanced the diuretic, natriuretic and ANP responses to 0.3 nmol/kg intravenous of hANP 99–126 in monkeys treated with vehicle or 10 μmol/kg intravenous of candoxatrilat. The sodium and ANP excretions stimulated by hANP 99–126 were positively correlated with each other and with the calculated intravenous sodium load in the presence or absence of candoxatrilat. 4. SQ 28 603 and candoxatrilat (0.3 to 10 μmol/kg intravenous) each produced significant, dose-related potentiation of the natriuretic, cGMP and ANP responses to 0.3 nmol/kg intravenous of hANP 99–126 in monkeys receiving 5 mL/kg + 0.2 mL/min saline. In addition, the highest dose of SQ 28 603 produced significant depressor activity. 5. In conclusion, the increased natriuretic activity of hANP 99–126 in sodium loaded monkeys was mediated, in part, by increased ANP delivery to the guanylate cyclase linked ANP receptors in the distal renal tubules.