Vasopeptidase inhibitors, such as omapatrilat are single molecules that simultaneously inhibit neutral endopeptidase (NEP) and angiotensin converting enzyme (ACE). In normotensive rats, a single dose of oral omapatrilat (10 mg/kg) and 1 mg/kg inhibited plasma ACE (P < .01) for 24 h and increased plasma renin activity for 8 h (P < .01). In vitro autoradiography using the specific NEP inhibitor radioligand 125I-RB104 and the specific ACE inhibitor radioligand 125I-MK351A showed omapatrilat (10 mg/kg) caused rapid and potent inhibition of renal NEP and ACE, respectively, for 24 h (P < .01). In spontaneously hypertensive rats, 10 days of oral omapatrilat (40 mg/kg/day) reduced blood pressure (vehicle 237 +/- 4 mm Hg; omapatrilat, 10 mg/kg, 212 +/- 4 mm Hg; omapatrilat 40 mg/kg, 197 +/- 4 mm Hg, P < .01) in a dose-dependent manner (10 v 40 mg/kg, P < .01). Left ventricular hypertrophy was significantly reduced by high-dose omapatrilat (vehicle 2.76 +/- 0.03 mg/g body weight; omapatrilat, 10 mg/kg, 2.71 +/- 0.02 mg/g; omapatrilat 40 mg/kg, 2.55 +/- 0.02 mg/g, P < .01) and omapatrilat also increased kidney weight compared to vehicle (both doses, P < .01). Omapatrilat caused significant inhibition of plasma ACE and increased plasma renin activity (both doses, P < .01), and in vitro autoradiographic studies indicated sustained inhibition of renal ACE and NEP (both doses, P < .01). Omapatrilat is a potent vasopeptidase inhibitor, and its antihypertensive effects are associated with inhibition of NEP and ACE at the tissue level and beneficial effects on cardiovascular structure. Relating the degree of tissue inhibition to physiologic responses may allow further definition of the role of local renin angiotensin and natriuretic peptide systems in the beneficial effects of vasopeptidase inhibitors.

These results indicate that selective NEP inhibition has major benefits in the regression of cardiac hypertrophy and reduction of fibrosis but has limited antihypertensive effects. The dual NEP/ACE inhibitor S21402 offered no advantage over the selective ACE inhibitor in terms of blood pressure reduction, or attenuation of cardiac hypertrophy and fibrosis, but did increase plasma ANP and blunted the reactive rise in renin with ACE inhibition. Further studies are needed to determine whether more complete blockade of the renin-angiotensin system with dual NEP/ACE inhibition results in additional benefits in terms of morbidity and mortality in cardiovascular disease.

Abstract-S21402 is a vasopeptidase inhibitor that simultaneously inhibits neutral endopeptidase (NEP) and angiotensinconverting enzyme (ACE). This study determined whether chronic treatment with S21402 produced different effects on sodium and water excretion, hormonal parameters, and cardiovascular structure compared with selective inhibition of ACE and NEP in a rat model of myocardial infarction-induced congestive heart failure (CHF). CHF rats received the vasopeptidase inhibitor (S21402, 100 mg ⅐ kg), or vehicle for 4 weeks. S21402 alone caused a diuresis and natriuresis (PϽ0.01) in CHF. After 4 weeks, blood pressure was lowered by captopril but not other treatments (PϽ0.01). Both S21402 and captopril increased plasma renin activity (PϽ0.01), all treatment lowered plasma aldosterone (PϽ0.05) and plasma natriuretic peptide levels were unchanged. In the kidney, S21402 inhibited NEP and ACE (PϽ0.01), SCH42495 inhibited NEP (PϽ0.01), and captopril inhibited ACE (PϽ0.01). Heart mass was reduced by all active treatments; captopril reduced left ventricular mass (PϽ0.01), SCH42495 reduced right ventricular mass (PϽ0.01), and S21402 decreased left (PϽ0.05) and right ventricular mass (PϽ0.01), atrial mass (PϽ0.05), and lung mass (PϽ0.01). In CHF, vasopeptidase inhibition with S21402 produces effects that differ from those of selective NEP or ACE inhibition. S21402 improved sodium and water excretion, reduced pulmonary congestion, and attenuated both right and left ventricular remodeling. These effects, which occurred in the absence of any hypotensive action, suggest that S21402 may offer several advantages over ACE inhibition alone in the treatment of heart failure. Key Words: vasopeptidase inhibitors Ⅲ neutral endopeptidase Ⅲ heart failure Ⅲ myocardial infarction Ⅲ natriuretic peptides Ⅲ cardiac remodeling C ongestive heart failure (CHF) is a progressive disease characterized by neurohormonal activation, salt and water retention, and cardiac remodeling. Inhibitors of angiotensin converting-enzyme (ACE), which prevent the formation of the constrictor, antinatriuretic, and trophic hormone angiotensin (Ang) II, attenuate ventricular remodeling, improve cardiac function and survival, and are standard treatment for CHF. 1 Atrial natriuretic peptide (ANP) is elevated in proportion to the degree of left ventricular dysfunction 2 and acts as an endogenous antagonist of the renin-angiotensin system (RAS) to cause natriuresis and diuresis, and vasodilation and suppression of the sympathetic nervous system. 3 An increase in endogenous levels of ANP by inhibition of its enzymatic degradation by neutral endopeptidase 24.11 (NEP) is a potential therapeutic strategy in heart failure. 4 Selective NEP inhibition has met with limited success as hyporesponsiveness to the biological actions of ANP occurs with increasing severity of heart failure, whereas the addition of an ACE inhibitor restores some benefits of NEP inhibition, including natriuresis. 5,6 Several compounds that simultaneously inhibit NEP and ACE, or vasopeptidase inhibitor...