Heterogeneities in regional volumes of distribution and flows in rabbit heart

The heterogeneity of volumes of distribution in the heart influences the rates of uptake and washout of substrates and metabolites; thus it is important to evaluate their variability in the normal heart. Several tracers were injected intravenously into anesthetized adult closed-chest rabbits, and time was allowed for equilibration in the heart. Tracer microspheres were injected into the left ventricular cavity at the apex for the measurement of regional flows, the chest was opened, another set of microspheres was injected, and the heart was frozen rapidly in situ with liquid nitrogen-cooled Freon-22. Each heart was divided into 72 pieces of less than 0.1 g weight, and the tracer content of each was determined by multichannel gamma-counting and the water content by desiccation. The regional myocardial flows were (closed chest) 0.62 +/- 0.16 ml.g-1.min-1 and (open chest) 0.63 +/- 0.37 ml.g-1.min-1. The volumes of distribution (ml/g) for the 432 pieces for six rabbits, given as mean +/- SD (% coefficient of variation), were as follows: for plasma, VP = 0.11 +/- 0.03 (26%); erythrocytes, VRBC = 0.041 +/- 0.015 (37%); vascular space, VV = 0.15 +/- 0.04 (26%); extracellular space, VECF = 0.33 +/- 0.05 (15%); interstitial space, VISF = 0.21 +/- 0.03 (15%); and water space, VW -0.79 +/- 0.022 (2.8%). Regional hematocrits were 77% +/- 9% of the large-vessel hematocrits.