Related Experiment Videos
Capillary supply and cardiac performance in the rabbit after chronic dobutamine treatment
1Department of Physiology, University of Birmingham, United Kingdom.
Insights
Increased cardiac contractility, not just blood flow, significantly promotes myocardial capillary growth. Chronic dobutamine treatment enhanced cardiac work capacity and capillary density in adult rabbit hearts.
Area of Science:
- Cardiovascular Physiology
- Myocardial Biology
- Angiogenesis Research
Background:
- Capillary growth in the adult heart is achievable with long-term vasodilator therapy.
- The role of increased cardiac workload in promoting myocardial capillary growth requires further investigation.
Purpose of the Study:
- To investigate the impact of enhanced stroke volume and/or contractility, alongside coronary blood flow, on myocardial capillary growth.
- To determine if increased cardiac workload can stimulate capillary angiogenesis in the adult heart.
Main Methods:
- New Zealand Red rabbits received chronic dobutamine infusion (20 µg/kg/min) for two weeks.
- Coronary blood flow, cardiac function (left ventricular dP/dtmax, noradrenaline-induced cardiac work), and myocardial capillary density were assessed.
- Radiolabeled microspheres, thermodilution, and alkaline phosphatase staining were employed for measurements.
Main Results:
- Dobutamine treatment resulted in a 29% increase in capillary density compared to controls, surpassing effects of vasodilators alone.
- Cardiac function improved, with significantly higher maximum stroke work and enhanced response to noradrenaline.
- Coronary blood flow remained unchanged, indicating enhanced efficiency of coronary flow utilization for cardiac work.
Conclusions:
- Increased myocyte stretch and contraction force, in addition to moderate blood flow changes, elicit greater capillary growth than increased blood flow alone.
- Chronic dobutamine treatment promotes adaptive enhancement of maximal cardiac work capacity through increased capillary supply.
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 less than 0.05) and coronary blood flow by 60% (NS).
Experimental Material:
New Zealand Red rabbits received dobutamine (20 micrograms.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/dtmax and maximum noradrenaline induced cardiac work, computed from cardiac output (thermodilution) and blood pressure. Capillary density.mm-2 was estimated in frozen 12 microns 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 less than 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.