Shunting of leukocytes in rabbit tenuissimus muscle

Leukocyte distribution was studied in 58 arterioles and capillaries constituting eight networks in the fascia adjacent to the rabbit tenuissimus muscle. Fluorescence video microscopy (acridine red) and digital image processing were used to visualize the leukocytes. Leukocyte concentration in the transverse arterioles leaving the muscle proper to irrigate the fascia was significantly elevated to 143 +/- 13% (mean +/- SE) of the systemic count. Leukocytes were found to further accumulate along the arteriolar tree, reaching 244 +/- 16% of systemic in the most remote branches. Leukocyte accumulation in the connective tissue can be calculated to lead to a decrease of leukocyte concentration in muscle capillaries to 89% of the systemic value. This shunting effect may be important in preventing leukocyte-induced capillary obstruction. At individual arteriolar bifurcations, leukocytes were found to preferentially enter the downstream branch with higher flow rate (regression coefficient 1.11 +/- 0.04, n = 100). This preferential distribution is quantitatively sufficient to account for the observed leukocyte distribution in the network.