Transcapillary osmotic flows in the in vitro perfused heart

Hearts were removed from rabbits anesthetized with pentobarbitol sodium, heparinized, and then perfused through the aorta with Ringer solution. Addition of sucrose to the perfusate caused an osmotic transcapillary flow (Jv). Measurements of Jv with two independent methods, one using the rate of organ weight change and the other the variation of effluent concentration of an impermeant dye (Blue dextran), agreed very closely, giving an initial Jv per unit concentration and wet heart weight of 0.306 (microliters/s) (mmol/l).g (corrected for viscosity, 25 degrees C). Because dye dilution was free of vascular volume interference, its agreement with weight measurements suggests that vascular volume changes were relatively small. Measurements using 51Cr-labeled erythrocytes supported the above conclusion. The effect of temperature and concentration on Jv was ascribed to viscosity changes. Organ condition remained stable for several hours, based on maximum ventricular pressure (107 +/- 6.4 cmH2O) and dP/dt (1,145 +/- 98 cmH2O/s) values close to those in blood-perfused rabbit hearts. Repeat weight response to osmotic testing showed approximately 5% variation during an experiment.