[Selective vasodilatation of the subepicardial coronary vasculature induced by carbochromen (author's transl)].

The effect of carbochromen on total and regional coronary blood flow was investigated in 6 anesthetized open-chest dogs. Total and regional myocardial blood flow was measured by radioactive microspheres, using the reference sample method. Left circumflex coronary flow was monitored by an electromagnetic flowmeter. In 4 dogs (Group 1) carbochromen was injected intravenously; in 2 dogs (Group 2) it was infused directly in the circumflex coronary artery. No significant changes in heart rate, left atrial left ventricular and aortic pressures were observed following carbochromen administration in both Groups. Left circumflex coronary blood flow progressively increased and a level slightly higher than peak reactive hyperemia was reached in both Groups. Regional myocardial blood flow measurements in Group 1 showed that the inner third of the left ventricular wall (ENDO) increased 2.7 times relative to control, the middle layer increased 3.4 times relative to control and the external third 4.5 times relative to control. A similar pattern was observed after intracoronary administration of carbochromen (Group 2). The ENDO/EPI flow ratio dropped from 0.98 +/- 0.16 to 0.58 +/- 0.18 in Group 1 and from 1.03 and 1.20 to 0.71 and 0.53 respectively in the two experiments of Group 2. Replacement of carbochromen with adenosine infusion in Group 2 produced a further increase in flow, mainly in the subendocardium resulting in ENDO/EPI flow ratio close to unity. These data demonstrate that the powerful coronary vasodilatory effect of carbochromen is not uniform being vasodilation more prominent in the vasculature of the external third of the left ventricular wall as compared to the inner third. Consequently a major redistribution of coronary blood flow, favouring the external layers of the left ventricle, results from carbochromen administration. This effect distinguishes carbochromen from other vasodilating stimuli than elicit a uniform response in the coronary vasculature and do not affect the ENDO/EPI ratio, including transient ischemia, adenosine, and dipyridamole.