Background Vasopeptidase inhibition is a new antihypertensive approach combining inhibition of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP), but severe oedema, mainly angio-oedema, has been reported. As ACE and NEP catalyse degradation of the permeability-increasing peptide bradykinin, and NEP also catalyses degradation of permeability-increasing peptides such as atrial natriuretic peptide, substance P, endothelin-1 and angiotensin II, vasopeptidase inhibition may increase microvascular permeability. Objective To analyse the effects of vasopeptidase inhibition on permeability. Design The study was performed on the autoperfused cat calf skeletal muscle, evaluating the effects on fluid and protein permeability of a clinically relevant dose of the vasopeptidase inhibitor, omapatrilat. The effects were compared with those of the vehicle, of selective ACE and NEP inhibition, and of omapatrilat during bradykinin receptor blockade. Methods Effects on fluid permeability were determined with a capillary filtration coefficient (CFC) technique, and effects on protein permeability were assessed from changes in the osmotic reflection coefficient for albumin. Results After 1.5 h of intravenous infusion of omapatrilat (0.35 mg/kg per hour), mean arterial pressure was reduced from 114 mmHg to 86 mmHg (P< 0.01) and skeletal muscle vascular resistance was reduced from 14.5 peripheral resistance units (PRU) to 11.5 PRU (P< 0.05). CFC was increased by 22% (P< 0.01) and the reflection coefficient was decreased by 17% (P< 0.01). Infusion of vehicle had no effects. Inhibition of NEP increased permeability without affecting blood pressure, whereas ACE inhibition decreased blood pressure without affecting permeability. The increase in permeability associated with omapatrilat was reduced by bradykinin blockade. Conclusions A clinically relevant antihypertensive dose of omapatrilat reduces vascular resistance and increases fluid and protein permeability, the permeability effect more by inhibition of NEP than by inhibition of ACE, by a mechanism involving bradykinin.

Recent studies have shown that angiotensin-converting enzyme (ACE) inhibitors attenuate endothelin-1 (ET-1)-induced hypertension, but the mechanisms for this effect have not been clarified. Initial experiments were conducted to contrast the effect of the ACE inhibitor enalapril, the combined ACE-neutral endopeptidase inhibitor omapatrilat, and the angiotensin II receptor antagonist candesartan on the hypertensive and renal response to ET-1 in anesthetized Sprague-Dawley rats. Acute intravenous infusion of ET-1 (10 pmol x kg(-1) x min(-1)) for 60 min significantly increased mean arterial pressure (MAP) from 125 +/- 8 to 145 +/- 8 mmHg (P < 0.05) and significantly decreased glomerular filtration rate (GFR) from 0.31 +/- 0.09 to 0.13 +/- 0.05 ml x min(-1) x 100 g kidney wt(-1). Pretreatment with enalapril (10 mg/kg iv) before ET-1 infusion inhibited the increase in MAP (121 +/- 4 vs. 126 +/- 4 mmHg) before and during ET-1 infusion, respectively (P < 0.05) without blocking the effect of ET-1 on GFR. In contrast, neither omapatrilat (30 mg/kg) nor candesartan (10 mg/kg) had any effect on ET-1-induced increases in MAP or decreases in GFR. To determine whether the effect of enalapril was due to the decrease in angiotensin II or increase in kinin formation, rats were given REF-000359 (1 mg/kg iv), a selective B(2) receptor antagonist, with or without enalapril before ET-1 infusion. REF-000359 completely blocked the effect of enalapril on ET-1 infusion (MAP was 117 +/- 5 vs. 135 +/- 5 mmHg before and during ET-1 infusion, respectively, P < 0.05). REF-000359 alone had no effect on the response to ET-1 infusion (MAP was 117 +/- 4 vs. 144 +/- 4 mmHg before and during ET-1 infusion, respectively, P < 0.05). REF-000359 with or without enalapril had no significant effect on the ability of ET-1 infusion to decrease GFR. These findings support the hypothesis that decreased catabolism of bradykinin and its subsequent vasodilator activity oppose the actions of ET-1 to increase MAP.

Recent studies have shown that angiotensin-converting enzyme (ACE) inhibitors attenuate endothelin-1 (ET-1)-induced hypertension, but the mechanisms for this effect have not been clarified. Initial experiments were conducted to contrast the effect of the ACE inhibitor enalapril, the combined ACE-neutral endopeptidase inhibitor omapatrilat, and the angiotensin II receptor antagonist candesartan on the hypertensive and renal response to ET-1 in anesthetized Sprague-Dawley rats. Acute intravenous infusion of ET-1 (10 pmol.kg -1 .min -1 ) for 60 min significantly increased mean arterial pressure (MAP) from 125 ± 8 to 145 ± 8 mmHg (P < 0.05) and significantly decreased glomerular filtration rate (GFR) from 0.31 ± 0.09 to 0.13 ± 0.05 ml.min -1 .100 g kidney wt -1 . Pretreatment with enalapril (10 mg/kg iv) before ET-1 infusion inhibited the increase in MAP (121 ± 4 vs. 126 ± 4 mmHg) before and during ET-1 infusion, respectively (P < 0.05) without blocking the effect of ET-1 on GFR. In contrast, neither omapatrilat (30 mg/kg) nor candesartan (10 mg/kg) had any effect on ET-1-induced increases in MAP or decreases in GFR. To determine whether the effect of enalapril was due to the decrease in angiotensin II or increase in kinin formation, rats were given REF-000359 (1 mg/kg iv), a selective B 2 receptor antagonist, with or without enalapril before ET-1 infusion. REF-000359 completely blocked the effect of enalapril on ET-1 infusion (MAP was 117 ± 5 vs. 135 ± 5 mmHg before and during ET-1 infusion, respectively, P < 0.05). REF-000359 alone had no effect on the response to ET-1 infusion (MAP was 117 ± 4 vs. 144 ± 4 mmHg before and during ET-1 infusion, respectively, P < 0.05). REF-000359 with or without enalapril had no significant effect on the ability of ET-1 infusion to decrease GFR. These findings support the hypothesis that decreased catabolism of bradykinin and its subsequent vasodilator activity oppose the actions of ET-1 to increase MAP.

Vasopeptidase inhibitors are a new class of antihypertensive drugs that are single molecules having dual inhibitory action on angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP). The best known drug in this class is omapatrilat, which has been proposed to be more efficacious than ACE inhibitors because of its ability to inhibit NEP and prevent the breakdown of atrial peptides and bradykinin. However, survival of endothelin (ET) may also be enhanced and therefore, NEP inhibitors may have limited efficacy under conditions of low renin and high ET production. The purpose of the current study was to contrast the effects of the ACE inhibitor, enalapril, with omapatrilat in a model of established hypertension where ACE inhibitors are ineffective, the deoxycorticosterone acetate (DOCA)-salt-treated rat. Two weeks after starting DOCA-salt treatment, rats were given either enalapril (10 mg/kg/day) or omapatrilat (30 mg/kg/day) for 5 days. Mean arterial pressure (MAP) measured by radiotelemetry in untreated DOCA-salt rats increased from 102±2 to 181±12 mm Hg (P<.05) as a result of DOCA-salt treatment for 3 weeks. MAP was unaffected by either enalapril (189±3 mm Hg) or omapatrilat (184±8 mm Hg). DOCA-salt treatment significantly increased urinary ET excretion compared to baseline (1.6±0.2 vs. 0.5±0.1 pmol/day). Administration of omapatrilat significantly increased urinary ET excretion in DOCA-salt rats (2.9±0.4 pmol/day) compared to enalapril-treated (1.6±0.2 pmol/day) or untreated (1.5±0.1 pmol/day) rats. These results indicate that combined ACE/NEP inhibition does not lower blood pressure in a model of established hypertension with high ET activity. These results also support the hypothesis that combined ACE/NEP inhibition can increase renal ET production.

The current study was conducted to determine the potential influence of ibuprofen on the renal and systemic response to AT1 receptor blockade in conscious rats developing spontaneous hypertension. Experiments used spontaneously hypertensive rats (SHR) during the early developmental phase of hypertension (6 to 7 wk old). Six groups of rats were given the following during a 2-wk treatment protocol: (1) candesartan cilexetil (AT1 receptor antagonist) at 1 mg/kg body wt per d; (2) candesartan cilexetil at 10 mg/kg per d; (3) ibuprofen at 30 mg/kg per d; (4) a combination of candesartan cilexetil at 1 mg/kg per d + ibuprofen; (5) candesartan cilexetil at 10 mg/kg per d + ibuprofen; and (6) untreated (controls). All compounds were added to the drinking water at concentrations adjusted to maintain the desired dosage. In the young untreated SHR, systolic arterial pressure significantly increased from 134+/-4 to 170+/-11 mmHg. Candesartan at 1 mg/kg per d prevented any increase in arterial pressure (131+/-5 mmHg at week 0 versus 131+/-4 mmHg at week 2). At a dose of 10 mg/kg per d, candesartan lowered arterial pressure from 131+/-2 to 91+/-4 mmHg. Ibuprofen treatment alone had no effect on the increase in arterial pressure observed in young SHR over the study period, and had no effect on the changes produced by candesartan at either dose. In the two groups of rats receiving candesartan at 10 mg/kg per d (with and without ibuprofen), a significant increase in urine volume and water intake was observed; urine volume rose from 9.5+/-1.0 to 22.9+/-1.1 ml/d in rats given only candesartan and from 11.5+/-0.7 to 22.0+/-0.6 ml/d in rats given candesartan + ibuprofen. Urine volume and water intake were unchanged in all other groups. These effects on water handling are consistent with previous findings that chronic angiotensin II inhibition inhibits water reabsorption in the kidney. These results demonstrate that nonsteroidal anti-inflammatory drug treatment has no effect on the antihypertensive efficacy and diuretic effects of AT1 receptor blockade in rats developing hypertension.