Microvascular effects and oedema formation of felodipine in man

The microvascular mechanisms responsible for oedema formation following the administration of calcium antagonists were studied in 10 healthy volunteers given intravenous felodipine and vehicle in a double-blind crossover trial. Plethysmography and laser Doppler flowmetry were used to measure microvascular parameters. Felodipine increased both skin and forearm blood flow. Due to a more pronounced inhibition of vascular tone in pre- than in postcapillary resistance vessels, capillary hydrostatic pressure increased and caused a net fluid filtration from blood to tissue. No evidence for increased vascular permeability was found. Under control conditions, a hydrostatic load led to fluid filtration despite constriction of resistance vessels and precapillary sphincters. Felodipine increased this fluid filtration and impaired the local vasoconstrictor responses. It is concluded that oedema formation induced by felodipine and other calcium antagonists can partly be ascribed to the vasodilatory effect of the drug (increased capillary pressure) and partly to interference with the local vascular control (probably the myogenic component) that protects dependent vascular regions from enhanced fluid filtration.