CAPILLARY SUPPLY AND CARDIAC-PERFORMANCE IN THE RABBIT AFTER CHRONIC DOBUTAMINE TREATMENT

Study objective - Growth of capillaries in the adult heart can occur after long term vasodilator treatment. This study investigated the effects of increased stroke volume and/or force of contraction in addition to coronary blood flow on myocardial capillary growth. Design - Coronary blood flow, cardiac function, and capillary supply were evaluated after chronic treatment with the inotrope dobutamine, at a dose shown to increase contraction force (dP/dt) acutely by 20% (p < 0.05) and coronary blood flow by 60% (NS). Experimental material - New Zealand Red rabbits received dobutamine (20-mu-g.kg-1.min-1 by intravenous infusion) for 2 weeks prior to measurements, under pentobarbitone anaesthesia, of coronary blood flow by radiolabelled microspheres, left ventricular dP/dt(max) and maximum noradrenaline induced cardiac work, computed from cardiac output (thermodilution) and blood pressure. Capillary density-mm-1 was estimated in frozen 12-mu-m sections of left ventricular myocardium stained for alkaline phosphatase. Measurements and main results - Capillary density was 29% greater after 2 weeks dobutamine infusion than in saline infused controls, which exceeds increases observed after longer infusions of vasodilators alone. Cardiac function was improved; maximum stroke work was significantly higher, stroke volume capacity larger, and dP/dt increased more during noradrenaline challenge. Coronary blood flow was unchanged in dobutamine treated hearts, hence efficiency of utilisation of coronary flow in terms of work was enhanced. Heart to body weight ratio was also greater after dobutamine, at 0.238(SEM 0.008) v 0.206(0.120), p < 0.05. Conclusions - Greater capillary growth can be elicited in the heart by increased stretch and/or force of contraction of myocytes in addition to moderate changes in blood flow than by increased blood flow alone. Chronic dobutamine treatment induced adaptive enhancement of maximal cardiac work capacity.