Arteriovenous distribution of transit times in cremaster muscle of the rat

Video digitization was applied to determine the arteriovenous transit time (TT) of blood flow between functionally paired arterioles and venules in cremaster muscle (rat). After a bolus injection of cell-free dye (FITC-Dextran) into a contralateral femoral artery, intensity-time curves (ITCs) of the fluorescent emissions were recorded in successive network divisions. TTs were calculated by cross-correlation of ITCs acquired from the video images digitized at rates of 5-10 frames/sec for up to 10 arteriole-venule (AV) pairs per video field whose position in the network was characterized in terms of centrifugal order of branching. Mean TT for first-order AV pairs averaged 3.74 +/- 1.62 (SD) sec and decreased significantly to 0.76 +/- 0.95 sec in the fifth-order pairs, with 75% of this reduction occurring between the first- and third-order pairs. A near threefold increase in coefficient of variation from first to fifth orders evidenced a marked increase in the spatial heterogeneity of TT at the level of the true capillaries. Comparison of TT with distance along the arterial tree from the tissue hilus revealed consistently stronger correlations than with AV order. These trends suggest that TT may be a superior indicator of the functional deployment of microvessels compared to branching order.