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Lang NN, Ahmad FA, Cleland JG, O'Connor CM, Teerlink JR, Voors AA, Taubel J, Hodes AR, Anwar M, Karra R, Sakata Y, Ishihara S, Senior R, Khemka A, Prasad NG, DeSouza MM, Seiffert D, Ye JY, Kessler PD, Borentain M, Solomon SD, Felker GM, McMurray JJV. Haemodynamic effects of the nitroxyl donor cimlanod (BMS-986231) in chronic heart failure: a randomized trial. Eur J Heart Fail 2021; 23:1147-1155. [PMID: 33620131 DOI: 10.1002/ejhf.2138] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 02/01/2021] [Accepted: 02/18/2021] [Indexed: 12/22/2022] Open
Abstract
AIMS Nitroxyl provokes vasodilatation and inotropic and lusitropic effects in animals via post-translational modification of thiols. We aimed to compare effects of the nitroxyl donor cimlanod (BMS-986231) with those of nitroglycerin (NTG) or placebo on cardiac function in patients with chronic heart failure with reduced ejection fraction (HFrEF). METHODS AND RESULTS In a randomized, multicentre, double-blind, crossover trial, 45 patients with stable HFrEF were given a 5 h intravenous infusion of cimlanod, NTG, or placebo on separate days. Echocardiograms were done at the start and end of each infusion period and read in a core laboratory. The primary endpoint was stroke volume index derived from the left ventricular outflow tract at the end of each infusion period. Stroke volume index with placebo was 30 ± 7 mL/m2 and was lower with cimlanod (29 ± 9 mL/m2 ; P = 0.03) and NTG (28 ± 8 mL/m2 ; P = 0.02). Transmitral E-wave Doppler velocity on cimlanod or NTG was lower than on placebo and, consequently, E/e' (P = 0.006) and E/A ratio (P = 0.003) were also lower. NTG had similar effects to cimlanod on these measurements. Blood pressure reduction was similar with cimlanod and NTG and greater than with placebo. CONCLUSION In patients with chronic HFrEF, the haemodynamic effects of cimlanod and NTG are similar. The effects of cimlanod may be explained by venodilatation and preload reduction without additional inotropic or lusitropic effects. Ongoing trials of cimlanod will further define its potential role in the treatment of heart failure.
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Affiliation(s)
- Ninian N Lang
- BHF Glasgow Cardiovascular Research Centre, Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - Faheem A Ahmad
- BHF Glasgow Cardiovascular Research Centre, Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - John G Cleland
- Robertson Centre for Biostatistics & Clinical Trials, University of Glasgow, Glasgow, UK.,National Heart & Lung Institute, Royal Brompton & Harefield Hospitals, Imperial College, London, UK
| | | | - John R Teerlink
- Department of Cardiology, San Francisco Veterans Affairs Medical Center and School of Medicine, University of California, San Francisco, San Francisco, CA, USA
| | - Adriaan A Voors
- Department of Cardiology, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands
| | | | - Anke R Hodes
- Department of Cardiology, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands
| | - Mohamed Anwar
- Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, UK
| | - Ravi Karra
- Department of Medicine, Duke Advanced Heart and Lung Failure Clinic, Duke University School of Medicine, Durham, NC, USA
| | - Yasushi Sakata
- Department of Cardiovascular Medicine, Osaka University Hospital, Suita, Osaka, Japan
| | - Shiro Ishihara
- Department of Cardiology, Nippon Medical School, Kawasaki-shi, Japan
| | - Roxy Senior
- Department of Cardiovascular Research, Northwick Park Hospital & Department of Cardiology, Royal Brompton Hospital, London, UK
| | - Abhishek Khemka
- Department of Cardiology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Narayana G Prasad
- Cardiovascular Division, Brigham and Women's Hospital, Boston, MA, USA
| | | | | | - June Y Ye
- Bristol-Myers Squibb, Princeton, NJ, USA
| | | | | | - Scott D Solomon
- Cardiovascular Division, Brigham and Women's Hospital, Boston, MA, USA
| | - G Michael Felker
- Division of Cardiology, Duke Clinical Research Institute (DCRI), Duke University School of Medicine, Durham, NC, USA
| | - John J V McMurray
- BHF Glasgow Cardiovascular Research Centre, Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
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Bezemer K, McLennan L, van Duin L, Kuijpers CJ, Koeberg M, van den Elshout J, van der Heijden A, Busby T, Yevdokimov A, Schoenmakers P, Smith J, Oxley J, van Asten A. Chemical attribution of the home-made explosive ETN – Part I: Liquid chromatography-mass spectrometry analysis of partially nitrated erythritol impurities. Forensic Sci Int 2020; 307:110102. [DOI: 10.1016/j.forsciint.2019.110102] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Revised: 12/12/2019] [Accepted: 12/13/2019] [Indexed: 12/24/2022]
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Daiber A, Oelze M, Coldewey M, Bachschmid M, Wenzel P, Sydow K, Wendt M, Kleschyov AL, Stalleicken D, Ullrich V, Mülsch A, Münzel T. Oxidative stress and mitochondrial aldehyde dehydrogenase activity: a comparison of pentaerythritol tetranitrate with other organic nitrates. Mol Pharmacol 2004; 66:1372-82. [PMID: 15331769 DOI: 10.1124/mol.104.002600] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mitochondrial aldehyde dehydrogenase (ALDH-2) was recently identified to be essential for the bioactivation of glyceryl trinitrate (GTN). Here we assessed whether other organic nitrates are bioactivated by a similar mechanism. The ALDH-2 inhibitor benomyl reduced the vasodilator potency, but not the efficacy, of GTN, pentaerythritol tetranitrate (PETN), and pentaerythritol trinitrate in phenylephrine-constricted rat aorta, whereas vasodilator responses to isosorbide dinitrate, isosorbide-5-mononitrate, pentaerythritol dinitrate, pentaerythritol mononitrate, and the endothelium-dependent vasodilator acetylcholine were not affected. Likewise, benomyl decreased GTN- and PETN-elicited phosphorylation of the cGMP-activated protein kinase substrate vasodilator-stimulated phosphoprotein (VASP) but not that elicited by other nitrates. The vasodilator potency of organic nitrates correlated with their potency to inhibit ALDH-2 dehydrogenase activity in mitochondria from rat heart and increase mitochondrial superoxide formation, as detected by chemiluminescence. In contrast, mitochondrial ALDH-2 esterase activity was not affected by PETN and its metabolites, whereas it was inhibited by benomyl, GTN applied in vitro and in vivo, and some sulfhydryl oxidants. The bioactivation-related metabolism of GTN to glyceryl-1,2-dinitrate by isolated RAW macrophages was reduced by the ALDH-2 inhibitors benomyl and daidzin, as well as by GTN at concentrations >1 microM. We conclude that mitochondrial ALDH-2, specifically its esterase activity, is required for the bioactivation of the organic nitrates with high vasodilator potency, such as GTN and PETN, but not for the less potent nitrates. It is interesting that ALDH-2 esterase activity was inhibited by GTN only, not by the other nitrates tested. This difference might explain why GTN elicits mitochondrial superoxide formation and nitrate tolerance with the highest potency.
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MESH Headings
- Aldehyde Dehydrogenase/metabolism
- Animals
- Aorta
- Benomyl/pharmacology
- Endothelium, Vascular/drug effects
- Endothelium, Vascular/physiology
- Esterases/metabolism
- Ethanol/pharmacology
- In Vitro Techniques
- Isometric Contraction/drug effects
- Isometric Contraction/physiology
- Mitochondria, Heart/drug effects
- Mitochondria, Heart/enzymology
- Mitochondria, Heart/metabolism
- Models, Animal
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/physiology
- Nitroglycerin/pharmacology
- Oxidative Stress/drug effects
- Oxidative Stress/physiology
- Pentaerythritol Tetranitrate/pharmacology
- Rats
- Rats, Wistar
- Reactive Oxygen Species/metabolism
- Vasodilator Agents/pharmacology
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Affiliation(s)
- Andreas Daiber
- Universitätsklinikum Eppendorf, Medizinische Klinik III, Angiologie und Kardiologie, Hamburg, Germany.
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Hacker A, Müller S, Meyer W, Kojda G. The nitric oxide donor pentaerythritol tetranitrate can preserve endothelial function in established atherosclerosis. Br J Pharmacol 2001; 132:1707-14. [PMID: 11309242 PMCID: PMC1572738 DOI: 10.1038/sj.bjp.0704021] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Recent results suggested that long-term treatment with a low dose of the organic nitrate pentaerythritol tetranitrate (PETN, 6 mg kg(-1) per day) for 16 weeks slightly decreases aortic superoxide production in normal rabbits. We sought to determine if PETN can preserve endothelium dependent relaxation (EDR) in atherosclerotic rabbits. Three groups of 9 - 10 New Zealand White rabbits received a cholesterol chow (0.75%) for 16 weeks. One group (CHOL16) served as control and two groups were fed for another 16 weeks a cholesterol-chow without (CHOL32) or with 6 mg PETN kg(-1) per day (PETN32). Isolated aortic rings of CHOL16 showed a typical impairment of EDR with a maximal relaxation at 1 microM acetylcholine of 28+/-16%. In CHOL32-rings EDR was completely impaired. In striking contrast, EDR in PETN32 (24+/-15%) was similar to that of CHOL16 indicating a protective effect of PETN on endothelial function. Vascular superoxide production measured with the lucigenin method was not different between the groups. Aortic lesion formation in PETN32 was smaller than in CHOL32 (P<0.008). The onset of copper-induced LDL-oxidation (lag-time) after 16 weeks of cholesterol feeding (214+/-9 min) was reduced in CHOL32 (168+/-24 min, P=0.035) but not in PETN32 (220+/-21 min). This indicates prevention of increased LDL oxidation by PETN. The halfmaximal effective vasodilator concentrations of PETN (in -logM) were identical in CHOL16 (7.9+/-0.1), CHOL32 (7.6+/-0.2) and PETN32 (7.7+/-0.2). Similar results were obtained with S-nitroso-N-acetyl-D,L-penicillamine. These data suggest that PETN can reduce the progression of lesion formation, endothelial dysfunction and of LDL-oxidation in established atherosclerosis.
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Affiliation(s)
- Andreas Hacker
- Institut für Pharmakologie, Heinrich-Heine-Universität, Moorenstr. 5, 40225 Düsseldorf, Germany
| | - Senta Müller
- Institut für Pharmakologie, Heinrich-Heine-Universität, Moorenstr. 5, 40225 Düsseldorf, Germany
| | - Wilfried Meyer
- Institut für Anatomie, Tierärztliche Hochschule Hannover, Bischofsholer Damm 15, 30173 Hannover, Germany
| | - Georg Kojda
- Institut für Pharmakologie, Heinrich-Heine-Universität, Moorenstr. 5, 40225 Düsseldorf, Germany
- Author for correspondence:
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Kojda G, Hacker A, Noack E. Effects of nonintermittent treatment of rabbits with pentaerythritol tetranitrate on vascular reactivity and superoxide production. Eur J Pharmacol 1998; 355:23-31. [PMID: 9754935 DOI: 10.1016/s0014-2999(98)00460-9] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Pentaerythritol tetranitrate is an organic nitrate ester that undergoes metabolization to pentaerythritol, pentaerythritol trinitrate, pentaerythritol dinitrate and pentaerythritol mononitrate. Recent data suggested that pentaerythritol tetranitrate is endowed with vasoprotective activities in experimental atherosclerosis. This study was undertaken to gain insight into the underlying mechanism. The basic mechanism of action of all pentaerythritol nitrates was evaluated by measuring liberation of nitric oxide (NO), stimulation of human soluble guanylate cyclase and vasorelaxation in rabbit aorta. A subsequent in vivo study in New Zealand White rabbits was performed to investigate the effects of a 4 months lasting nonintermittent oral treatment with 6 mg pentaerythritol tetranitrate kg(-1) day(-1) on vascular superoxide production, endothelium dependent vasorelaxation and vasorelaxation to pentaerythritol tetranitrate itself. The formation rates of NO from the pentaerythritol nitrates (100 microM, n = 5) in presence of 5 mM cystein were (in nM min(-1)): 62.1 +/- 3.2 (pentaerythritol tetranitrate), 21.3 +/- 0.9 (pentaerythritol trinitrate), 6.4 +/- 0.6 (pentaerythritol dinitrate) and 3.2 +/- 0.4 (pentaerythritol mononitrate). Similarly, the pD2 values (-log M) for half-maximal activation of soluble guanylate cyclase decreased from pentaerythritol tetranitrate (3.391 +/- 0.09, n = 4) to pentaerythritol mononitrate (2.655 +/- 0.04, n = 3) as did the pD2 values (in -log M) for half-maximal relaxation of rabbit aortic rings (n = 7) from pentaerythritol tetranitrate (8.3 +/- 0.17) to pentaerythritol mononitrate (5.0 +/- 0.11). Significant correlations were found between the NO formation rates and the pD2 values for enzyme stimulation (r = 0.98, P = 0.002) and vasorelaxation (r = 0.90, P = 0.049) suggesting that these effects of the pentaerythritol nitrates were mediated by NO. The results of the in vivo study showed that aging induces a significant increase of aortic superoxide production (median values, n = 10) from 2.45 nM mg(-1) min(-1) (age 7 months) to 3.39 nM mg(-1) min(-1) (age 11 months, P < 0.01) that was prevented by concurrent treatment with pentaerythritol tetranitrate (2.76 nM mg(-1) min(-1)). In vitro vasorelaxation to pentaerythritol tetranitrate was identical in all groups indicating absence of nitrate tolerance. Endothelium-dependent vasorelaxation was also identical in all groups. These data suggest that oral treatment with pentaerythritol tetranitrate reduces vascular oxidant stress by an NO-dependent pathway, which may contribute to the vasoprotective activity of pentaerythritol tetranitrate in experimental atherosclerosis.
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Affiliation(s)
- G Kojda
- Institut für Pharmakologie, Heinrich-Heine-Universität, Düsseldorf, Germany.
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Chung SJ, Fung HL. A common enzyme may be responsible for the conversion of organic nitrates to nitric oxide in vascular microsomes. Biochem Biophys Res Commun 1992; 185:932-7. [PMID: 1378270 DOI: 10.1016/0006-291x(92)91716-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
We compared the nitric oxide (NO)-generating behavior of nitroglycerin (NTG), pentaerythritol trinitrate (PEtriN) and isosorbide dinitrate (ISDN), in the microsomal preparation of bovine coronary artery smooth muscle cells. The comparative NO generating activities among these nitrates were consistent with their relative reported vasodilating activities. Consistent with our previous observations with NTG, 400 microM bromosulfophthalein did not affect NO generation from PEtriN and ISDN in vascular microsomes while 400 microM 1-chloro-2,4-dinitrobenzene completely inhibited NO generation from these nitrates. Gel filtration chromatography with solubilized microsomes of bovine aortic smooth muscle cells showed the primary activity of NO generation from all three nitrates to be eluted at about 200 kD, consistent with that found with solubilized microsomes from the bovine coronary artery microsomes. These results suggest that organic nitrates may be converted to NO by one common enzyme in vascular microsomes.
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Affiliation(s)
- S J Chung
- Department of Pharmaceutics, School of Pharmacy, State University of New York, Buffalo 14260
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Hatano Y, Imai R, Komatsu K, Mori K. Intravenous administration of isosorbide dinitrate attenuates the pressor response to laryngoscopy and tracheal intubation. Acta Anaesthesiol Scand 1989; 33:214-8. [PMID: 2728825 DOI: 10.1111/j.1399-6576.1989.tb02893.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
In order to evaluate the effect of isosorbide dinitrate (ISDN), administered as a bolus intravenous injection, on the circulatory response to tracheal intubation, mean arterial pressure (MAP), and heart rate (HR) in response to laryngoscopy for 30 s followed by tracheal intubation were compared in patients not receiving ISDN (control) and receiving 40 micrograms/kg or 80 micrograms/kg of ISDN 45 s before starting laryngoscopy. Each group consisted of 10 patients undergoing elective surgery. Forty-five seconds after starting laryngoscopy, MAP was significantly (P less than 0.01) lower in patients receiving 80 micrograms/kg ISDN than in those receiving no or 40 micrograms/kg ISDN. HR increased to a similar extent in the three groups. These results indicate that a bolus injection of ISDN (80 micrograms/kg) is a simple, practical and highly effective means of attenuating the hypertensive response to direct laryngoscopy and tracheal intubation.
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Affiliation(s)
- Y Hatano
- Department of Anesthesia, Kyoto University Hospital, Japan
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8
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King SY, Fung HL. Pharmacokinetics of pentaerythritol tetranitrate following intra-arterial and oral dosing in the rat. J Pharm Sci 1986; 75:247-50. [PMID: 3701607 DOI: 10.1002/jps.2600750308] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The pharmacokinetics of pentaerythritol tetranitrate (2,2-bis(hydroxymethyl)-1,3-propanediol tetranitrate, 1) were studied in rats following a single intra-arterial or oral dose (2 mg/kg) of the 14C-labeled drug. Blood levels of the tetranitrate and its metabolites were determined using a thin-layer radiochromatographic procedure. The apparent systemic clearance of 1 was 0.61 +/- 0.16 L/min/kg (mean +/- SD, n = 6) which exceeded the value of normal cardiac output in rats. The steady-state volume of distribution was 4.2 +/- 1.1 L/kg (n = 6), and the elimination half-life was estimated at 5.8 +/- 0.6 min (n = 6). Blood levels of 1 were only detectable (higher than 4.0 ng/mL) in three of the six rats examined after the oral dose. The trinitrate derivative (2,2-bis(hydroxymethyl)-1,3-propanediol trinitrate, 2) the active metabolite of 1, was not detectable following oral dosing with the tetranitrate. The oral bioavailability of 1 was in the range of 0-8%. In spite of the low water solubility of 1 (i.e., 1 microgram/mL), a rather high fraction of the radioactive oral dose [25.7 +/- 10.3% (n = 4) versus 62.4 +/- 14.5% (n = 4) from the intra-arterial dose] was recovered in the urine. A significant portion of the intra-arterial dose (32.7 +/- 11.0%, n = 4) was eliminated in feces, indicating enterohepatic recycling of radioactivity. Analysis of the metabolite pattern in urine indicated extensive metabolism of 1, 2, and the dinitrate derivative 3 (2,2-bis(hydroxymethyl)-1,3-propanediol dinitrate). Less than 0.2% of the dose was recovered as unchanged drug and 2 following either route of administration.
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Fiedler VB, Nitz RE. Effects of molsidomine, nitroglycerin, and isosorbide dinitrate on the coronary circulation, myocardial oxygen consumption, and haemodynamics in anaesthetized dogs. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1981; 317:71-7. [PMID: 6792547 DOI: 10.1007/bf00506260] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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Watkins RW, Davidson IW. Comparative effects of nitroprusside and nitroglycerin; actions on phasic and tonic components of arterial smooth muscle contraction. Eur J Pharmacol 1980; 62:191-200. [PMID: 6769682 DOI: 10.1016/0014-2999(80)90275-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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Shane SJ, Iazzetta JJ, Chisholm AW, Berka JF, Leung D. Plasma concentrations of isosorbide dinitrate and its metabolites after chronic high oral dosage in man. Br J Clin Pharmacol 1978; 6:37-41. [PMID: 666946 PMCID: PMC1429383 DOI: 10.1111/j.1365-2125.1978.tb01679.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
1 We have previously reported that vasodilator headache due to isosorbide dinitrate (ISDN) can be circumvented by using small 'priming' doses for an induction period of 1-2 weeks, after which it is possible to increase to dose rapidly to 360-720 mg, daily without recurrence of headache and without toxicity. The present study corroborates this earlier finding. 2. Chronic oral administration of doses of ISDN of this order of magnitude results in prolonged high plasma concentrations of the parent compound, as well as higher levels of the metabolites 2-ISMN and 5-ISMN. 3. It is our thesis that chronic high oral dosage of ISDN saturates the intrahepatic biotransformation process, and allows high concentrations of ISDN and its metabolites to enter the systemic circulation.
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Mikkelsen E, Andersson KE, Bengtsson B. Effects of verapamil and nitroglycerin on contractile responses to potassium and noradrenaline in isolated human peripheral veins. ACTA PHARMACOLOGICA ET TOXICOLOGICA 1978; 42:14-22. [PMID: 414517 DOI: 10.1111/j.1600-0773.1978.tb02166.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Isolated ring preparations of human vein were contracted by potassium (127 mM) and noradrenaline (1.8 X 10(-5) M). The potassium-induced contracture developed more rapidly and had a higher maximum amplitude than that produced by noradrenaline. Addition of phentolamine (10(-5) M) reduced the amplitude of the potassium contracture by 22% and abolished the noradrenaline response. Verapamil and nitroglycerin relaxed preparations contracted by potassium and noradrenaline, and, when added prior to stimulation, reduced the contractile responses to these agents. Both verapamil and nitroglycerin inhibited the contractile effect of noradrenaline more strongly than that of potassium. After immersion of the preparations for 30 min. in a calcium-free medium, the responses to potassium and noradrenaline were reduced to 21.3 +/- 2.5% and 7.1 +/- 0.8%, respectively, of the control. Addition of verapamil caused a further reduction of the response to potassium, but not of that to noradrenaline. Nitroglycerin caused a further reduction of the contractions induced by both agents. When the calcium concentration in the extracellular medium was increased from 0 to 4 mM, the contractile responses to potassium and noradrenaline returned to the control level. Both verapmil and nitroglycerin inhibited the contractile responses to calcium; the inhibiting effects of verapamil were significantly more marked than those of nitroglycerin. Tachyphylaxis to nitroglycerin was demonstrated on contractions induced by potassium, but not on noradrenaline-produced responses.
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