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Acute changes in microvascular blood flow distribution in the myocardium of the rat during partial occlusion of the right coronary artery; effects of dihydroergotamine.

Changes in blood flow during restricted right coronary perfusion were studied in anesthetized rats. By use of a carotid-coronary shunt system, coronary perfusion pressure could be reduced to 40 mm Hg, leading to a fall in flow from 0.9 ml/min to 0.3 ml/min. The perfusion pattern within the flow-restricted area was determined by labelling the blood plasma with fluoresceinisothiocyanate (FITC) globulin (demonstration of the entire vascular system) and lissamine-rhodamine B200 (RB200) globulin (demonstration of actually perfused myocardial capillaries). In histological sections, arterial ramifications were evaluated with respect to the arrival of RB200 in their branches. Large filling defects were observed when flow was obstructed. After 10s labelling, in ramifications with a feeding artery larger than 15 microns in diameter, 10.5% of the vessels displayed dye in only one of the branches, and 13.5% in neither of the two branches. For smaller ramifications (less than 8 microns), these values amounted to 17.5% and 41.5%, respectively. A similar pattern was observed after vascular labelling for 60 s. When dihydroergotamine (2.0 micrograms/kg i.v.) was applied one minute after onset of occlusion, the perfusion inhomogeneity was significantly reduced (labelling in one branch and in none of the two, respectively: greater than 15 microns: 60% and 10.0%; less than 8 microns: 13.5%, and 26%). It can therefore be concluded that dihydroergotamine reduces hypoperfusion-induced inhomogeneity in myocardial blood flow.