Regional blood flow and oxygenation of the rabbit heart subjected to acute coronary occlusion — effect of phenoxybenzamine

Abstract

The effect of phenoxybenzamine (2 mg/kg) on subepicardial (EPI) and subendocardial (ENDO) blood flow and oxygenation was determined in ischemic and non-ischemic areas of hearts subjected to acute coronary occlusion in 24 pentobarbital-anesthetized open-chest New Zealand white rabbits. Ten minutes after occlusion, blood flow measure with radioactive microspheres was 57% lower in the occluded region compared to the non-occluded area. There were no EPI vs. ENDO differences at this time. Phenoxybenzamine was then administered and one hour after occlusion, flow in all areas was significantly reduced. Flow in the occluded area fell to a lesser extent than in the non-occluded area. ENDO flows were lower than EPI in both areas. After occlusion, relative tissue PO2 fell significantly in the affected areas. No other changes were significant. Phenoxybenzamine lowered relative tissue PO2 in the occluded ENDO but had no other effect. This indicates that the relationship of O2 supply to consumption is preserved in the heart after phenoxybenzamine except in the occluded ENDO. In this region, the fall in relative tissue PO2 indicates that the reduction in flow is large compared to any change in metabolism. The reduction in this relationship may be due to reduced perfusion pressure for collateral flow and/or "coronary steal".

REGIONAL O2 SUPPLY/CONSUMPTION IN NORMAL AND ISCHAEMIC RABBIT MYOCARDIUM: EFFECT OF NIFEDIPINE

“…Therefore the rabbit ischaemic model should be useful for visualizing any benefits in O2 supp1y:demand balance exerted by nifedipine. The extensive collateral network in the rabbit heart was determined by Weiss (1982), where LAD occlusion decreased coronary blood flow by approximately 50%, as was observed also in the present study. This is in contrast to the 70-75% reductions in blood flow in the dog occlusion model (Gorman & Sparks 1980;Conway & Weiss 1982).…”

“…Regional blood flow decreases with LAD occlusion were similar to those decreases seen in other ischaemic rabbit preparations (Weiss 1982;Briden et al 1979), averaging 51% in this experiment. When the low dose of nifedipine was given, there was no significant increase in blood flow in either nonoccluded or occluded regions, despite the maintenance of systolic blood pressure.…”

“…This is in contrast to the 70-75% reductions in blood flow in the dog occlusion model (Gorman & Sparks 1980;Conway & Weiss 1982). Rabbits also have a high degree of noncollateral overlap flow, comprising approximately 21% of the blood flow to an occluded region (Weiss 1982). For this reason, tissue samples in this study were obtained either from the core of the darkened ischaemic area, or from nonoccluded tissue in the left ventricular free wall as far as possible away from the ischaemic zone.…”

“…An anaesthetized open-chest rabbit model was employed for observation of 0 2 supply and 0 2 consumption in the nifedipine infused animal. The rabbit was chosen for demonstration of nifedipine's effects because of the extensive collateral development in the rabbit heart compared to the dog (Weiss 1982). Any changes in blood flow to the ischaemic region of a rabbit heart should thus be more dramatic.…”

Effect of ouabain on O2 supply/demand in normal and ischemic heart

“…Small-vessel blood content can be used as an estimate of the number of open capillaries. It has, however, been found that rabbits have better collateral circulation (18). The estimated values are shown in Figure 1.…”