Regional distributions of blood flow and tissue uptake rates of vitamin B₁₂ and albumin within single rabbit skeletal muscles

Abstract

The mechanism underlying the marked regional variations in blood flow within single skeletal muscles has not been identified. The present investigation was prompted by previous data pointing to a regional distribution of the number of perfused vessels as one possible determinant for the heterogeneous perfusion pattern. We examined this possibility by assessing the regional tissue uptake rates of vitamin B12 and albumin assuming that these are related to the number of perfused vessels. This is the first study that has included simultaneous measurements of regional blood flow and of regional tissue uptake rates of vitamin B12 and albumin within single skeletal muscles in the intact animal. The microsphere method was adopted to measure regional blood flow in 0.25 g muscle regions in awake and in anaesthetized rabbits. Various tracers were used to assess the regional distributions of tissue uptake rates and of vascular and interstitial volumes. Albeit displaying a marked regional heterogeneity, neither the tissue uptake rate of vitamin B12 nor that of albumin were correlated to regional blood flow (P less than 0.05) at rest (awake or anaesthetized rabbits) or during exercise hyperaemia (anaesthetized). At rest, but not during exercise, the distributions of regional tissue uptake rates of the two tracers showed a striking bimodal pattern. Vascular and interstitial volumes showed minimal interregional variations. The lack of correlation between regional blood flow and tissue uptake rates and the minute interregional variation in vascular volume, argue against variations in the number of perfused vessels as the explanation for the regional heterogeneity in blood flow.