Concentration dependent effects of calcium blockade on vessel diameter and microvascular macromolecular clearance.
The dose-dependents effects of topically applied verapamil (a calcium entry blocker) on vessel diameter and macromolecular clearance (as an index of permeability) were investigated in the hamster cheek pouch. Verapamil at concentrations between 10(-10)M and 10(-7)M produced a gradual and parallel increase in both vessel diameter and in macromolecular clearance. At concentrations between 10(-7)M and 10(-5)M verapamil greatly increased macromolecular transport, but only modestly increased vessel diameter. Our data indicate that low doses of verapamil influence microvascular transport by modulation of flow and associated changes in microvascular pressure, while doses of verapamil greater than or equal to 10(-7)M produce a more direct effect on microvascular permselectivity.