Effects of leukocyte activation on capillary hemodynamics in skeletal muscle.

Leukocytes may be an important determinant of microvascular resistance, particularly during pathological states that cause cell activation and cytoplasmic stiffening. Significant mechanisms include capillary plugging and venular adhesion. Previous quantitative studies on leukocyte-capillary plugging focused solely on arteriolar-capillary branchpoints. There are no quantitative data on plugging throughout the capillary network either under normal conditions or after leukocyte activation. Plugging measurements were made throughout capillary networks at both arteriolar-capillary and capillary-capillary branchpoints in spinotrapezius muscle of anesthetized rats under normal physiological conditions and after leukocyte activation by superfusion with 1 x 10(-7) M N-formyl-methionyl-leucylphenylalanine (FMLP). These data were used to estimate the increase in microvascular flow resistance due to leukocyte plugging. The increase was 1.1% in control and 15.9% in the activated state. On an individual network basis, this represents an average 23-fold increase (P < 0.002) in network resistance, suggesting that leukocyte activation has a significant impact on microvascular blood flow.