Measurement of coronary blood flow velocity in conscious rats

This study describes a technique for the continuous recording of coronary blood flow velocity (CBV) in conscious unrestrained rats. A pulsed Doppler flow probe consisting of a 1-mm2 crystal mounted in a 4-mm suction cup was positioned over the left coronary artery of pentobarbital sodium-anesthetized rats. The probe was held in place with mild suction and sutured to the surface of the myocardium. Probes were connected to a pulsed Doppler flowmeter, which measures Doppler shift and provides an index of blood flow velocity. While rats were still anesthetized, the measurement of CBV was validated by determining that CBV peaked during diastole and increased in parallel with arterial pressure. Phasic CBV signals obtained in conscious rats were similar to those observed in anesthetized animals. Intravenous infusion of dipyridamole (0.5-3 mg.kg-1 x mg-1) produced a dose-dependent increase in CBV and decrease in coronary vascular resistance in conscious unrestrained rats 7 days after placement of the probe. Light microscopic review of cardiac tissue from instrumented rats revealed minimal epicardial reaction (fibrin deposition) restricted to the immediate area of the probe without distortion of the coronary architecture, edema, inflammation, or necrosis compared with controls. Heart weight-to-body weight ratios of instrumented rats were also not different from those of control rats. This study describes the first technique by which CBV can be measured continuously in chronically instrumented rats.