Angelo J. Trapani

Norepinephrine produces tension through electromechanical coupling in rabbit ear artery.

Abstract Membrane potential (E m ) and contractile responses to norepinephrine (NE) were measured to determine whether electromechanical coupling is important in the rabbit ear artery. NE contraction and depolarization of the vascular muscle cells were both dose dependent, with a positive correlation between depolarization and tension generated by the vessel. These studies suggest that NE regulates vascular muscle contraction through an E m signal in the rabbit ear artery.

Cgs 35601 and its Orally Active Prodrug Cgs 37808 as Triple Inhibitors of Endothelin-converting Enzyme-1, Neutral Endopeptidase 24.11, and Angiotensin-converting Enzyme

CGS 35601 is a potent triple inhibitor of endothelinconverting enzyme-1, neutral endopeptidase 24.11, and angiotensinconverting enzyme. It inhibited the activities of these three enzymes with IC50 values of 55, 2 and 22 nM, respectively. In conscious rats, CGS 35601 suppressed the big endothelin-1-induced pressor response by 82% and 72% at 30 and 120 minutes, respectively, following injection at a dose of 10 mg/kg, intravenously. At the same dose, CGS 35601 increased plasma atrial natriuretic peptide (ANP) immunoreactivity by 170% for up to 4 hours in conscious rats infused with ANP, and it inhibited the angiotensin I-induced pressor response by 74-94% within the first 2 hours after dosing. Similar in vivo activities were also observed with its orally active prodrug, CGS 37808. This compound blocked the big endothelin-1- induced pressor response by 71% and 67% at 30 and 120 minutes, respectively, after an oral dose of 10 mgEq/kg in conscious rats. It also increased plasma ANP immunoreactivity by 103% for up to 4 hours and inhibited the angiotensin I-induced pressor response by an average of 49% within the first 4 hours after the same dosing regimen. By suppressing the biosyntheses of endothelin-1 and angiotensin II, two potent vasoconstrictors, while simultaneously potentiating the circulating levels of ANP, a vasorelaxant and diuretic, CGS 35601 and CGS 37808 may represent novel agents for the treatment of cardiovascular and renal diseases.

Benzofused Macrocyclic Lactams as Triple Inhibitors of Endothelin-converting Enzyme, Neutral Endopeptidase 24.11, and Angiotensin-converting Enzyme

The purpose of this study was to identify endothelin-converting enzyme (ECE) inhibitors that also possess inhibitory activity for neutral endopeptidase 24.11 (NEP) and angiotensin-converting enzyme (ACE). The ortho-substituted benzofused macrocyclic lactams, such as CGS 26670, are generally potent NEP inhibitors but poor ACE inhibitors. CGS 26670 inhibited ECE activity with an IC50 of 600 nM, whereas it inhibited NEP and ACE activities with IC50 values of 0.9 and > 10,000 nM, respectively. This compound also prevented the conversion of big endothelin-1 (big ET-1) to ET-1 by denuded porcine coronary arterial smooth muscle with an IC50 of 200 nM. The ACE inhibitory activity is greatly is greatly improved in metasubstituted benzofused macrocyclic lactams. For example, CGS 26582 inhibited ECE, NEP, and ACE activities with IC50 values of 620, 4, and 175 nM, respectively. When injected at 30 mg/kg i.v. in conscious rats, followed by a challenge with big ET-1 at 1 nmol/kg i.v., this compound suppressed by 44% the increase in mean arterial blood pressure owing to the generation of ET-1 by ECE. Because ECE, NEP, and ACE play regulatory roles in cardiovascular and renal function, triple inhibitors of these enzymes may represent a novel class of agents for treatment of cardiovascular and renal diseases.

Trophic effect of norepinephrine on the rat portal vein in organ culture.

Rat portal veins were maintained in organ culture to study the development of charac-teristic denervation changes and a possible trophic effect of the neurotransmitter norepinephrine (NE). Vessels maintained in organ culture for 2 days showed supersensitivity to NE and Ba2+, a more rapid rate of relaxation from a Ba2+contracture, and partial depolarization of the myovascular cells. All of these changes except the quicker relaxation from Ba2+contracture could be prevented by incubating the preparations in a NE-containing medium. This evidence suggests that functional changes in vascular muscle cells are caused by the removal of a trophic influence of NE, but can be prevented by NE replacement. However, the failure of NE in the culture media to prevent the increased rate of relaxation from Ba2+contracture found after 2 days in organ culture suggests that NE is not the only trophic influence acting on the portal vein. In addition, incubation of veins in a NE-containing medium produced a marked subsensitivity to the contractile effects of NE, but not Ba2+, and thus possible desensitization of noradrenergic receptors. The data thus support a trophic role for NE in the rat portal vein. Circ Res 47: 770-775, 1980

Design and synthesis of a potent and selective endothelin-converting enzyme inhibitor, CGS 35066.

CGS 26303 has previously been shown to inhibit human endothelin converting enzyme-1 (ECE-1) with an IC50 of 410 nM and to be efficacious in several animal disease models. However, it is a more potent inhibitor of neutral endopeptidase 24.11 (NEP) with an IC50 of 1 nM. The aim of this study was to optimize CGS 26303 for greater potency and selectivity towards ECE-1 inhibition. The in vivo activity of the compounds was assessed by inhibition of the big endothelin-1 (ET-1)-induced pressor response in anesthetized rats at 90 min after treatment with a dose of 10 mg/kg, i.v. Under these conditions, CGS 26303 inhibited the pressor response to big ET-1 by 50%. Replacement of the biphenyl and tetrazol groups in CGS 26303 with a dibenzofuran and carboxylic acid, respectively, yielded CGS 35066, a potent ECE-1 inhibitor having an IC50 of 22 nM. In contrast, these substitutions markedly weakened the NEP inhibitory activity of the compound to an IC50 of 2.3 microM. CGS 35066 also exhibited a potent and sustained ECE-1 inhibitory activity in vivo, blocking the pressor response to big ET-1 by 84%. Its orally active prodrug, CGS 35339, was obtained by introducing two phenyl groups at the phosphonic acid substituent in CGS 35066. Therefore, CGS 35066 and CGS 35339 represent novel compounds for assessing the pathogenic role of ET-1 overproduction in various disease states.

Pharmacological properties of CGS 35066, a potent and selective endothelin-converting enzyme inhibitor, in conscious rats.

The purpose of this study was to examine the pharmacologic properties of CGS 35066, a novel aminophosphonate inhibitor of endothelin-converting enzyme-1 (ECE-1). CGS 35066 inhibited the activity of human ECE-1 and rat kidney neutral endopeptidase 24.11 (NEP) in vitro with IC50 values of 22 +/- 0.9 nM and 2.3 +/- 0.03 microM, respectively. The in vivo effects of CGS 35066 were characterized in conscious, catheterized rats. At 30 and 120 min after treatment with vehicle, big endothelin-1 (big ET-1, 0.3 nmol/kg i.v.) produced increases in mean arterial pressure (MAP) of 982 +/- 31 and 992 +/- 43 mmHg x min (area under the curve), respectively. Doses of 0.3, 1.0, 3.0 and 10.0 mg/kg i.v., of CGS 35066 blocked these pressor responses by 61 +/- 7, 78 +/- 4, 93 +/- 4 and 98 +/- 2% at 30 min (p < 0.05 compared with vehicle controls, all doses), and by 29 +/- 7, 63 +/- 5, 63 +/- 5 and 84 +/- 10% at 120 min (p < 0.05, all doses). In contrast, the pressor effect (58 +/- 6 mmHg) of angiotensin-I (300 ng/kg i.v.) was unaffected by the ECE-1 inhibitor (10 mg/kg i.v.) indicating the absence of activity against angiotensin-converting enzyme. In rats infused with atrial natriuretic peptide (ANP), CGS 35066, at 1 mg/kg, had no effect on plasma irANP; however, irANP levels were doubled at a dose of 30 mg/kg. These results demonstrate that CGS 35066 is the most potent and selective ECE inhibitor identified to date.

Comparative Central and Peripheral Antihypertensive Mechanisms of Urapidil and Prazosin

The central effects of urapidil were investigated in conscious rats with sinoaortic denervation. Intraventricular urapidil administration (40 to 100 micrograms) produced a transient depressor response followed by a pressor response coupled with tachycardia. In comparison, intraventricular prazosin administration (2.5 to 5.0 micrograms) produced only a prolonged depressor effect. The effect of intravenously administered urapidil (3 mg/kg) on arterial pressure, heart rate, and mesenteric, renal, and hindquarter resistances was then compared with that of prazosin (0.5 mg/kg) in conscious rats with sinoaortic denervation, instrumented with pulsed Doppler flow probes. Both agents caused similar significant decreases in arterial pressure and vascular resistances, but urapidil decreased renal resistance significantly more than did prazosin. Prazosin increased heart rate, whereas no change was found with urapidil. Prazosin blocked the pressor and regional constrictor effects of intravenously administered norepinephrine more effectively than urapidil.

Pharmacologic profile of CGS 24128, a potent, long-acting inhibitor of neutral endopeptidase 24.11.

We compared the pharmacologic profiles of thiorphan, a neutral endopeptidase (NEP) inhibitor which is cleared rapidly from the circulation, and CGS 24128, an inhibitor with a much longer half-life (t1/2). Thiorphan and CGS 24128 inhibited NEP in vitro with IC50 values of 5.0 +/- 0.2 and 4.3 +/- 0.2 nM, respectively. After administration at 10 mg/kg intravenously (i.v.), the concentrations of CGS 24128 in the plasma were > 500 nM for 4 h but plasma thiorphan was detectable for only 60 min. Thiorphan 3 mg/kg administered intraarterially (i.a.) increased plasma atrial natriuretic peptide immunoreactivity (ANPir) levels by 58 +/- 12% in rats administered exogenous ANP(99-126). This response lasted < 60 min, whereas the same dose of CGS 24128 produced an average increase of 191 +/- 19% in ANPir concentrations that persisted for 4 h. ANP-induced (1 microgram/kg i.v.) natriuresis was significantly potentiated in anesthetized rats pretreated (60 min) with a bolus of CGS 24128 10 mg/kg i.v. The change in urinary sodium excretion (UNaV) produced by ANP was 28.8 +/- 4.0 and 15.8 +/- 1.8 muEq/kg/min in CGS 24128- and vehicle-treated rats, respectively. ANP-induced natriuresis was also greater during continuous infusion of thiorphan (5 mg/kg bolus + 0.1 mg/kg/min i.v.; delta UNaV = 29.2 +/- 5.8 and 13.8 +/- 3.2 muEq/kg/min in drug- and vehicle-treated rats, respectively) but not when thiorphan was administered as a bolus (10 mg/kg i.v.) 60 min before the ANP challenge.(ABSTRACT TRUNCATED AT 250 WORDS)