Comparison of relaxation induced by glyceryl trinitrate, isosorbide dinitrate, and sodium nitroprusside in bovine airways
Abstract
Nitrates are generally regarded as bronchial smooth muscle relaxants. However, reports about the clinical efficacy of the nitrates in the treatment of asthma are conflicting. In the present study, the relaxant effects of glyceryl trinitrate, isosorbide dinitrate, sodium nitroprusside, and isoproterenol were measured and compared in vitro in airway preparations isolated from variously sized airways in bovine lung. Strips of trachealis from cervical and thoracic ends of the trachea and rings of intrapulmonary bronchi of various diameters (14 to 1 mm outer diameters) were mounted for recording of isometric tension. Submaximal tone was induced using 10(-6) M carbachol, and responses to cumulatively increasing concentrations of glyceryl trinitrate, isosorbide dinitrate, sodium nitroprusside, or isoproterenol were measured. Isoproterenol (10(-8) to 10(-4) M) was equiactive as a relaxant in all preparations. Glyceryl trinitrate (10(-7) to 10(-5) M) relaxed trachealis, but was progressively and significantly less effective as a relaxant as the diameters of the bronchial rings decreased. Although less potent than isoproterenol, sodium nitroprusside (10(-6) to 10(-4) M) was effective in relaxing all the airway preparations. Similar to gl...Continue Reading
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