Platelet-activating factor stimulates protein tyrosine kinase in hamster cheek pouch microcirculation

We studied the interactions between platelet-activating factor (PAF) and protein tyrosine kinase (PTK) in the modulation of microvascular responses in the hamster cheek pouch using intravital microscopy and computer-assisted image analysis. Changes in arteriolar diameter and in integrated optical intensity (IOI; an index of vascular permeability) were measured. Fluorescein isothiocyanate-labeled dextran 150 (FITC-Dx 150) served as a tracer for macromolecular transport. Genistein and tyrphostin 25, two PTK inhibitors, were applied topically in separate experiments. Pretreatment with 10^-4, 10^-6, and 10^-8 M genistein and with tyrphostin 25 at 10^-5 and 10^-7 M attenuated the maximal increment in mean IOI (±SE) induced by PAF at 10^-7 M (19.9 ± 5.3, 21.5 ± 4.5, 58.5 ± 11.4, 28.7 ± 7.6, and 35.0 ± 10.9 vs. 70.7 ± 8.9 units, respectively). Pretreatment with PTK inhibitors resulted in vasodilation but did not inhibit PAF-induced vasoconstriction. Our results suggest that PTK represents a biochemical pathway involved in the PAF modulation of microvascular permeability but not PAF modulation of arteriolar tone.