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Twenty-five patients (aged 18 to 72 years), who recovered after the first bleed from a cerebral aneurysm, were operated on under neuroleptanaesthesia. Isoflurane was added to induce hypotension. It was found that the required hypotension (51 (SEM 1) mmHg) could be obtained and maintained at much lower isoflurane concentrations (less than 1%) after blockade of the angiotensin converting enzyme activity by enalaprilat (2.5 mg i.v.) than without such inhibition. During the hypotension which lasted 78 (SEM 10) min, only minor adjustments of the isoflurane concentration (0.70 (0.04%) were needed. The desired level of hypotension was obtained with preservation of the cardiac output and without tachycardia. No resistance to the blood pressure lowering effect of isoflurane was observed. On recovery from anaesthesia, a small increase of blood pressure above control values was seen in 16 patients and was easily reversed by small doses of clonidine (mean total dose: 220 (61) micrograms). The operative conditions were excellent and the postoperative recovery was uneventful and complete in 23 patients.
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Podocytes were incubated with a medium of mesangial cells co-incubated with aIgA1, which was isolated from IgAN patients, and enalaprilat (10(-5) M), valsartan (10(-5) M) and anti-mouse tumour necrosis factor-alpha antibody (50 ng mL(-1)) separately. Nephrin expression in podocytes was measured by real-time polymerase chain reaction and Western blot analysis.
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Although early studies suggested little role for angiotensin-converting enzyme (ACE) inhibitors in older hypertensive patients, more careful evaluation has confirmed their efficacy and good tolerability. Although the elderly tend to have low plasma renin levels, the fall in blood pressure after ACE inhibitors is at least as great (and in several studies greater) than in younger age groups. Because several ACE inhibitors, including captopril and enalaprilat, are eliminated by the kidneys, there are predictable age-related effects on pharmacokinetics. Reduced renal clearance will contribute, at least in part, to the enhanced intensity and duration of action seen in elderly patients. However, not all the effects of age on the kinetics and dynamics of ACE inhibitors are predictable. Studies with perindopril and benazepril in the elderly confirm the efficacy of this group of drugs but highlight other pharmacokinetic differences. ACE inhibitors are effective in reducing blood pressure and can be considered for wider use in elderly hypertensives.
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Angiotensin converting enzyme (ACE) plays a critical role in the circulating or endocrine renin-angiotensin system (RAS) as well as the local regulation that exists in tissues such as the myocardium and skeletal muscle. Here we report the high-resolution crystal structures of testis ACE (tACE) in complex with the first successfully designed ACE inhibitor captopril and enalaprilat, the Phe-Ala-Pro analogue. We have compared these structures with the recently reported structure of a tACE-lisinopril complex [Natesh et al. (2003) Nature 421, 551-554]. The analyses reveal that all three inhibitors make direct interactions with the catalytic Zn(2+) ion at the active site of the enzyme: the thiol group of captopril and the carboxylate group of enalaprilat and lisinopril. Subtle differences are also observed at other regions of the binding pocket. These are compared with N-domain models and discussed with reference to published biochemical data. The chloride coordination geometries of the three structures are discussed and compared with other ACE analogues. It is anticipated that the molecular details provided by these structures will be used to improve the binding and/or the design of new, more potent domain-specific inhibitors of ACE that could serve as new generation antihypertensive drugs.
Furosemide-131I-hippuran renography with ACE inhibition is highly predictive in identifying patients with RVH.
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The pharmacodynamic profile of the new angiotensin-converting enzyme (ACE) inhibitor moexipril and its active diacid, moexiprilat, was studied in vitro and in vivo. In vitro, moexiprilat exhibited a higher inhibitory potency than enalaprilat against both plasma ACE and purified ACE from rabbit lung. Upon oral administration of moexipril (10 mg/kg/day) to spontaneously hypertensive rats, plasma angiotensin II concentration decreased to undetectable levels, plasma ACE activity was inhibited by 98% and plasma angiotensin I concentration increased 8.6-fold 1 h after dosing. At 24 h, plasma angiotensin I and angiotensin II concentrations had returned to pretreatment levels, whereas plasma ACE activity was still inhibited by 56%. Four-week oral administration of moexipril (0.1-30 mg/kg/day) to spontaneously hypertensive rats lowered blood pressure and differentially inhibited ACE activity in plasma, lung, aorta, heart and kidney in a dose-dependent fashion. Equidose treatment (10 mg/kg/day) with moexipril and enalapril over 4 weeks led to comparable decreases in blood pressure, inhibition of plasma ACE and reduction of plasma angiotensinogen and to a similar attenuation of the pressor responses to angiotensin I and potentiation of the depressor responses to bradykinin. In contrast, ACE inhibition in aorta, heart and lung was significantly greater with moexipril than with enalapril, whereas in the kidney both drugs inhibited ACE activity to a similar extent. In summary, moexipril is an orally active ACE inhibitor that is comparable to enalapril in potency and duration of antihypertensive activity. The results of the present study demonstrate that 1) the antihypertensive potency of a given ACE inhibitor cannot be predicted from its in vitro characteristics and 2) the degree of blood pressure reduction does not correlate with tissue ACE inhibition.
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We determined whether local bradykinin production modulates cardiac adrenergic activity. Depolarization of guinea pig heart sympathetic nerve endings (synaptosomes) with 1 to 100 mmol/L K+ caused the release of endogenous norepinephrine (10% to 50% above basal level). This release was exocytotic, because it depended on extracellular Ca2+, was inhibited by the N-type Ca(2+)-channel blocker omega-conotoxin and the protein kinase C inhibitor Ro31-8220, and was potentiated by the neuronal uptake-1 inhibitor desipramine. Typical of adrenergic terminals, norepinephrine exocytosis was enhanced by activation of prejunctional angiotensin AT1-receptors and attenuated by adrenergic alpha 2-receptors, adenosine A1-receptors, and histamine H3-receptors. Exogenous bradykinin enhanced norepinephrine exocytosis by 7% to 35% (EC50, 17 nmol/L), without inhibiting uptake 1. B2-receptor, but not B1-receptor, blockade antagonized this effect. The kininase II/angiotensin-converting enzyme inhibitor enalaprilat and the addition of kininogen or kallikrein enhanced norepinephrine exocytosis by approximately equal to 6% to 40% (EC50, 20 nmol/L) and approximately equal to 25% to 60%, respectively. This potentiation was prevented by serine protease inhibitors and was antagonized by B2-receptor blockade. Therefore, norepinephrine exocytosis is augmented when bradykinin synthesis is increased or when its breakdown is inhibited. This is the first report of a local kallikrein-kinin system in adrenergic nerve endings capable of generating enough bradykinin to activate B2-receptors in an autocrine/paracrine fashion and thus enhance norepinephrine exocytosis. This amplification process may operate in disease states, such as myocardial ischemia, associated with severalfold increases in local kinin concentrations.
The contribution of nonangiotensinergic effects of converting enzyme inhibitors to their hemodynamic effects in patients with chronic heart failure is not clear. A comparison of the effects of renin and converting enzyme inhibition should help to clarify this issue.
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The purpose of this study was to determine whether angiotensin-converting enzyme is present in cultured human bronchial epithelial cells and which types of epithelial cells possess this enzyme. It is well known that serum promotes squamous differentiation of airway epithelial cell culture in vitro. We found that whole-cell homogenates of both basal (serum-untreated) and squamous-differentiated bronchial epithelial cells degraded hippuryl-L-histidyl-L-leucine, a synthetic substrate for angiotensin-converting enzyme. Analysis of RNA expression by reverse transcription-polymerase chain reaction (RT-PCR) showed the presence of mRNA for angiotensin-converting enzyme in both types of cells. In addition, we found that squamous cells secreted the enzyme into the culture medium more than basal cells did. Angiotensin-converting enzyme inhibitors (imidaprilat, enalaprilat) inhibited the enzyme activity in bronchial epithelial cells with an IC50 of 0.9-3.6 nM. Exogenously added bradykinin was degraded to bradykinin-(1-5), an inactive fragment, in the squamous cell cultures. Our data indicate the presence of angiotensin-converting enzyme in cultured human bronchial epithelial cells and also that the enzyme is secreted by squamous differentiated cells.
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The aims of this study were to 1) determine whether renal localization of aliskiren and its antihypertensive and renoprotective effects persist after administration of the drug is stopped and 2) define the renal localization of aliskiren by light microscopy autoradiography. Hypertensive double transgenic rats (dTGR) overexpressing genes for human renin and angiotensinogen were treated with aliskiren (3 mg·kg(-1)·day(-1) sc; osmotic minipumps) or enalapril (18 mg/l in drinking water). After a 2-wk treatment, dTGR were assigned to either continued treatment with aliskiren ("continued"), or to cessation of their respective treatment ("stopped") for a 3-wk washout. One week of treatment with aliskiren and enalapril reduced blood pressure and albuminuria vs. baseline. After cessation of either treatment, blood pressure had returned to pretreatment levels and albuminuria remained relatively low for 1 wk, but rose thereafter similarly in both groups. In contrast, renal mRNA for transforming growth factor-β and renal collagen IV was reduced by aliskiren (continued and stopped groups), but not after cessation of enalapril. Similar patterns were found for collagen IV protein expression. Even 3 wk after stopping aliskiren treatment, renal levels of the drug exceeded its IC50, whereas enalaprilat was not detected. To localize aliskiren accumulation, Wistar rats were treated with [(3)H]-aliskiren for 7 days. Autoradiography demonstrated specific labeling in glomeruli, arterioles, and afferent arterioles as well as in the distal nephron. Labeling could still be observed even after 7 days' washout. These results suggest that the renophilic properties of aliskiren are different from enalapril and could have contributed to the renoprotective mechanism of this renin inhibitor.
The ACE inhibitors increase bradykinin, an agonist of NO synthase (NOS). Nitric oxide inhibits beta-adrenergic myocardial contractility in patients with heart failure.