Vital microscopic studies on the capillary distribution of leukocytes in the rat cremaster muscle

Leukocyte capillary distribution was studied with vital fluorescence microscopy in the rat cremaster muscle. Ten terminal arterioles, each in a different animal, with 2 to 7 capillaries and with a total leukocyte flux ranging from 97 to 571 cells, were analysed. Nonparametric statistics was used for the analyses of the experimental data. In order to characterize the pathways for leukocyte flux in the networks, the leukocyte concentration for each capillary was calculated in relation to the network inflow leukocyte concentration and to the bifurcation inflow leukocyte concentration. The study shows a strong positive correlation between the relative capillary leukocyte concentration and the capillary volume flow and the position of the capillary in the network, respectively. There was no correlation between the relative capillary leukocyte concentration and capillary branching angle. A relative leukocyte concentration above unity, indicating an enrichment of leukocytes, was found in capillaries with a high volume flow and in capillaries located at the downstream end of the arterioles. In addition, the analyses show a very strong correlation between capillary volume flow and the position of the capillary along the arteriole, the capillaries located at the downstream end having the highest volume flows. In conclusion, the present study provides evidence for the existence of volume flow dependent preferential pathways for leukocyte passage across the capillary network in the rat cremaster muscle.