phosphoramidon and Body-Weight

Using perfused hearts from streptozotocin-induced long-term diabetic rats, we studied the coronary vasoconstrictor effect of the endothelin-1 (ET-1) precursor big ET-1 and also whether this response was modulated by N(epsilon)-(carboxymethyl)lysine (CML; a representative advanced glycation end product that is implicated in the pathogenesis of diabetic vasculopathy). The big ET-1-induced vasoconstriction (a) developed more rapidly (i.e., was greater in the first 30 min) in the diabetic group than in the age-matched controls, and (b) in each group was largely suppressed by phosphoramidon [nonselective endothelin-converting enzyme (ECE)/neutral endopeptidase (NEP) inhibitor] or CGS35066 (selective ECE inhibitor), but not by thiorphan (selective NEP inhibitor). The ET-1 release occurring after treatment with big ET-1, which was greater in diabetic coronary arteries than in the controls, was reduced by CGS35066. The dose-response curve for ET-1 was shifted to the left in the diabetics, so that at some lower doses of ET-1 the vasoconstriction was greater than in the controls. CML enhanced big ET-1- or ET-1-induced vasoconstriction in the controls, but not in the diabetics. Finally, the plasma level of CML was higher in diabetic than in control rats. These findings suggest (a) that the increased responsiveness to big ET-1 shown by diabetic coronary arteries may be attributable both to a more rapid conversion of big ET-1 to ET-1 (by ECE), allowing it to exert its contractile activity, and to an increased vascular sensitivity to ET-1, and (b) that CML may be at least partly responsible for the diabetes-associated enhancement of big ET-1-mediated coronary vasoconstriction.

Topics: Animals; Aspartic Acid Endopeptidases; Benzofurans; Blood Glucose; Body Weight; Coronary Vessels; Diabetes Mellitus, Experimental; Endothelin A Receptor Antagonists; Endothelin B Receptor Antagonists; Endothelin-1; Endothelin-Converting Enzymes; Enzyme Inhibitors; Glycopeptides; Heart; Lipids; Lysine; Male; Metalloendopeptidases; Myocardium; Oligopeptides; Organ Size; Organophosphonates; Peptides, Cyclic; Perfusion; Piperidines; Rats; Rats, Wistar; Receptor, Endothelin A; Receptor, Endothelin B; Thiorphan; Vasoconstriction

Neutral endopeptidase 24.11 (NEP), widely distributed in the body, hydrolyzes and inactivates a number of endogenous vasoactive peptides, some of which could alter various functions of cells present in the arterial wall. Recently NEP has been found to exist in the vascular endothelium. The aim of this study was to assess the influence of chronic NEP inhibition by daily administration of UK79300 (candoxatril), an orally active NEP inhibitor (NEPI), on the development of atherosclerotic changes in high-cholesterol-fed rabbits. Male New Zealand White rabbits were fed for 8 weeks as follows: normal rabbit diet (Normal, n = 15), 1.5% cholesterol diet (Cholesterol, n = 15), or 1.5% cholesterol diet containing NEPI (20 mg.kg-1.d-1) (Cholesterol+NEPI, n = 15). At the end of the dietary period, NEPI treatment was found to suppress the surface area of the aorta covered by plaques (% surface area: Cholesterol, 59 +/- 6 versus Cholesterol+NEPI, 36 +/- 7, P < .01) and decreased contents of cholesterol and cholesterol esters in the aortas. NEPI also reduced plasma total cholesterol by 27% of Cholesterol rabbits (1781 +/- 130 mg/dL). The endothelial function, estimated by the endothelium-dependent relaxation of the isolated aortas in response to acetylcholine, was preserved in Cholesterol+NEPI rabbits compared with that in Cholesterol rabbits. NEP enzymatic activities in plasma and the particulate fraction of the homogenates from the aortas in Cholesterol rabbits were both increased, 3.1- and 3.9-fold, respectively, above those in Normal rabbits, but the activities in Cholesterol+NEPI rabbits were significantly lower than those in Cholesterol rabbits. UK73967, an active form of UK79300, or phosphoramidon partly reversed the atherosclerotic impairment of relaxation of the isolated thoracic aortic rings from Cholesterol rabbits in response to exogenous additions of C-type natriuretic peptide (CNP) and substance P, which are NEP substrates known to exist endogenously in the vascular endothelium. The results suggest that the increased NEP activity plays a significant role in atherogenesis, and NEPIs might be therapeutically useful in the prevention of atherosclerosis. Reduction of plasma cholesterol and suppression of degradations in the arteries of endogenously released CNP, substance P, or possibly other kinins known to have anti-atherosclerotic actions may at least partially contribute to the inhibitory effects of NEPIs on atherosclerotic changes.

Topics: Administration, Oral; Animals; Aorta, Thoracic; Arteriosclerosis; Atrial Natriuretic Factor; Body Weight; Cholesterol, Dietary; Diet, Atherogenic; Drug Evaluation, Preclinical; Enzyme Inhibitors; Glycopeptides; Hemodynamics; Hypercholesterolemia; Indans; Lipids; Male; Natriuretic Peptide, C-Type; Neprilysin; Nitroprusside; Organ Culture Techniques; Propionates; Proteins; Rabbits; Substance P; Vasodilation

Alpha-naphthylthiourea when injected intraperitoneally to rats (10 mg kg-1 i.p.) produced lung oedema as indicated by an increase in lung weight/body ratio and pleural effusion reaching a maximum within 4 hours. Prior intravenous single bolus injection of endothelin-1 elicited a significant and dose-dependent inhibition in both parameters. However, prior i.v. injection of angiotensin II using relatively higher doses did not alter the oedema-producing effect of alpha-naphthylthiourea indicating a characteristic for endothelin-1. The inhibitory effect of endothelin-1 on pleural effusion is more prominent than lung weight/body weight ratio. The resolution of lung oedema by single bolus i.v. injection of endothelin-1 is probably due to the acute long-lasting and potent vasoconstrictor effect of the peptide and its large accumulation in lung tissue. Phosphoramidon, an inhibitor of endothelin converting enzyme, did not alter the oedema producing effect of alpha-naphthylthiourea indicating the lack of the participation of endothelin-peptide cascade to this pathological event. Bosentan, a non-selective receptor blocker of endothelin-1, did not inhibit the preventive effect of the peptide against alpha-naphthylthiourea-induced lung oedema. Possible mechanisms of the acute effect of endothelin-1 on lung oedema are discussed.

Topics: Angiotensin II; Animals; Aspartic Acid Endopeptidases; Body Weight; Bosentan; Endothelin-1; Endothelin-Converting Enzymes; Glycopeptides; Male; Metalloendopeptidases; Organ Size; Pleural Effusion; Protease Inhibitors; Pulmonary Edema; Rats; Sulfonamides; Thiourea

1. Chronic hypoxic rats are always polycythaemic. It is possible that an increase in packed cell volume may enhance erythrocyte trapping with a consequent increase in renal damage after renal ischaemia. These experiments were designed to assess renal functional changes after renal arterial occlusion in chronic hypoxic rats. 2. Chronic hypoxic rats were prepared by exposure (15h/day) to an altitude chamber (5486m) for 4 weeks. 3. After 45 min of left renal arterial occlusion, there were significant decreases in the excretion of potassium, p-aminohippurate and inulin and in the p-aminohippurate extraction ratio in 12 sea level ischaemic insulted kidneys. In 12 chronic hypoxic rats, the same parameters were changed after left renal ischaemia but only the p-aminohippurate ratio was significantly altered. 4. Administrations of 1 or 5 mg/kg phosphoramidon did not cause any significant improvement in the measured renal parameters in both kidneys and in both groups of rats after ischaemia. 5. In the second experiment, the rats were challenged by rapid infusion of 10 ml of saline intravenously, and urine was collected for 90 min from each ureter. Four hours after left renal arterial occlusion, the insulted kidney showed increased water and sodium excretion in both sea level and chronic hypoxic rats. However, 24 h after left renal ischaemia, the responses of sea level and chronic hypoxic rats were different. Urinary excretion was significantly reduced in sea level rats, but was almost normal in chronic hypoxic rats. 6. This report suggests that some beneficial factors after chronic hypoxia might play important roles in reducing the damage after renal ischaemia.

Topics: Acute Kidney Injury; Animals; Body Weight; Chronic Disease; Glycopeptides; Hematocrit; Hypoxia; Insulin; Ischemia; Kidney; Male; p-Aminohippuric Acid; Potassium; Rats; Rats, Sprague-Dawley

Neutral endopeptidase 3.4.24.11 (NEP) has been identified as the major atrial natriuretic factor (ANF) degrading enzyme in rat kidney, therefore, suggesting a possible role for this enzyme in blood volume and pressure regulation. Various experimentally induced and genetically hypertensive rat models have been used to test NEP inhibitors. The presence of different isoforms of NEP in the various hypertensive rat models would have relevance when searching for novel NEP inhibitors. Therefore, we compared the properties of NEP in kidney cortex homogenates in order to test for possible differences in the following hypertensive rat models and their appropriate controls: spontaneously hypertensive rats (SHR), Wistar Kyoto strain (WKY), DOCA-salt hypertensive rats, and Sprague Dawley control rats (SD). No relevant differences were found when comparing the following parameters: (1) specific activity (mean: 204 U/mg protein), (2) Michaelis constant (mean: 280 microM), (3) IC50 of thiorphan (mean: 6.5 nM) and phosphoramidon (mean: 54 nM), (4) pH profiles (optimum at pH 8.0), (5) heat inactivation profiles (half-life 20 min at 65 degrees C), (6) immunotitration of kidney cortex homogenates, (7) molecular weight as determined by gel filtration (92,000 Dalton) and (8) affinity chromatography with concanavalin A. Without evidence for the presence of different NEP isoforms, it is unlikely that divergent findings in DOCA-salt rats and SHR using a given NEP inhibitor are due to isoforms of NEP.

Topics: Animals; Body Weight; Desoxycorticosterone; DNA; Glycopeptides; Hot Temperature; Hydrogen-Ion Concentration; Hypertension; Kidney Cortex; Neprilysin; Organ Size; Protein Denaturation; Proteins; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Sprague-Dawley; Salts; Thiorphan