Leukocyte adherence in arterioles following extravascular tissue trauma

To study the effect of tissue injury on leukocyte adherence in arterial microvessels, small regions of tissue adjacent to vessels in the wing of the bat were exposed to single doses of laser irradiation. The experimental design provided data on the effect of (1) tissue injury of variable extent but a fixed distance from the arterial vessel and (2) tissue injury of a constant extent but at varying distances from the arterial microvessels. Preirradiation controls showed that normally no leukocytes could be observed either adherent to, or rolling along, the vessel wall. Following injury and after a quite variable latency time there was a time-dependent increase in the number of observed leukocytes. Using the latency time as an index, an analysis was applied to test the hypothesis that the laser irradiation released some substance which subsequently diffused to the vessel wall. The results of this analysis have shown that all the experimental latency time data can be explained on the basis of a model in which a diffusable “leukotactic” substance is released from the laser site in an amount that is proportional to the surface area of induced injury. Though the precise nature of the released substance is speculative, analysis shows that the process is characterized by an effective diffusion coefficient of approximately 7.0 × 10⁻⁷ which is suggestive of highmolecular-weight substance.