EVALUATION OF SQ-28-603, AN INHIBITOR OF NEUTRAL ENDOPEPTIDASE, IN CONSCIOUS MONKEYS

The potent neutral endopeptidase inhibitor SQ 28 603 (N-(2-(mercaptomethyl)-1-oxo-3-phenylpropyl)-beta-alanine) significantly increased excretion of sodium from 4.9 +/- 2.3 to 14.3 +/- 2.1-mu-equiv./min and cyclic 3'.5'-guanosine monophosphate from 118 +/- 13 to 179 +/- 18 pmol/min after intravenous administration of 300-mu-mol/kg (approximately 80 mg/kg) in conscious female cynomolgus monkeys. SQ 28 603 did not change blood pressure or plasma atrial natriuretic peptide concentrations in the normal monkeys. In contrast, 1-h infusions of 3, 10, or 30 pmol . kg-1 . min-1 of human atrial natriuretic peptide lowered blood pressure by -3 +/- 4, -9 +/- 4, and -27 +/- 3 mmHg (1 mmHg = 133.322 Pa), increased cyclic guanosine monophosphate excretion from 78 +/- 11 to 90 +/- 6,216 +/- 33, and 531 +/- 41 pmol/min, and raised plasma atrial natriuretic peptide from 7.2 +/- 0.7 to 21 +/- 4, 62 +/- 12, and 192 +/- 35 fmol/mL without affecting sodium excretion. In monkeys receiving 10 pmol . kg-1 . min-1 of atrial natriuretic peptide, 300-mu-mol/kg of SQ 28 603 reduced mean arterial pressure by -13 +/- 5 mmHg and increased sodium excretion from 6.6 +/- 3.2 to 31.3 +/- 6.0-mu-equiv./min, cyclic guanosine monophosphate excretion from 342 +/- 68 to 1144 +/- 418 pmol/min, and plasma atrial natriuretic peptide from 124 +/- 8 to 262 +/- 52 fmol/mL. In conclusion, SQ 28 603 stimulated renal excretory function in conscious monkeys, presumably by preventing the degradation of atrial natriuretic peptide by neutral endopeptidase.