Nitrovasodilators ITF 296 and isosorbide dinitrate exert antiischemic activity by dilating coronary penetrating arteries

We examined the effect of the novel nitrovasodilator ITF 296 and isosorbide dinitrate (ISDN) on myocardial blood flow (BF) distal to a coronary artery stenosis. Eleven dogs with a Doppler velocity probe, hydraulic occluder, and indwelling microcatheter in the left anterior descending coronary artery (LAD) were studied during treadmill exercise in the presence of a coronary artery stenosis. On separate days, the effects of ITF 296 in doses of 4 and 20 μg/kg/min i.v. or ISDN 20 μg/kg/min i.v. were compared. Coronary pressure distal to the stenosis was maintained constant during the control period and after administration of either nitrovasodilator. Neither ITF 296 nor ISDN significantly altered heart rate (HR), arterial blood pressure (BP), or left ventricular enddiastolic pressure (LVEDP). In the presence of a stenosis that decreased distal coronary pressure to 58 ± 4 mm Hg, mean myocardial BF measured with microspheres was 0.91 ± 0.08 ml/min/g in the LAD-dependent region and 2.36 ± 0.11 ml/min/g in the posterior control region, respectively. With no change in distal coronary pressure, ITF 296 increased mean BF in the LAD region to 1.25 ± 0.05 ml/min/g (4 μg/kg/min i.v.) and 1.40 ± 0.10 ml/min/g (20 μg/kg/min i.v.), whereas ISDN (20 μg/kg/min i.v.) increased flow to 1.28 ± 0.18 ml/min/g (each p < 0.05). The increase in BF occurred exclusively in the deeper layers, with no change in subepicardial BF. Consequently, the endocardial/epicardial (endo/epi) BF ratio increased from 0.33 ± 0.04 during control stenosis to 0.70 ± 0.10 after ITF 296 (20 μg/kg/min), and to 0.56 ± 0.08 after ISDN (each p < 0.05). Neither ITF 296 nor ISDN had an effect on myocardial BF in the normally perfused control region. Therefore, both ITF 296 and ISDN improved BF to the deeper myocardial layers distal to a coronary artery stenosis. This effect occurred without alterations in stenosis severity or diastolic intraventricular pressure, suggesting that these agents act by dilating the penetrating arteries which deliver BF to the subendocardium.