DIFFERENTIAL EFFECTS OF THE CALCIUM ANTAGONIST, VERAPAMIL, ON LUMEN SIZES OF TERMINAL ARTERIOLES AND MUSCULAR VENULES IN THE RAT MESENTERIC, PIAL AND SKELETAL MUSCLE MICROVASCULATURES

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Abstract
The actions of the local perivascular application of verapamil to rat mesenteric, pial and cremaster muscle arterioles and muscular venules (15 to 35 μm i.d.), was examined in situ, at the microcirculatory level, by use of a high-resolution closed circuit television microscope recording system. Local application of verapamil (1 to 100 μg) to cremaster muscle arterioles and venules of the rat induces dose-dependent vasodilatation and increased perfusion of capillaries. However, neither arteriolar nor muscular venular lumen sizes and capillary blood flow of the rat mesenteric or pial vasculatures were altered by even high doses of verapamil. Although these direct in situ microvascular findings do indicate that verapamil can induced dilatation of microscopic resistance and capacitance vessels in skeletal muscle, our data do not support the concept that verapamil induces non-specific peripheral vasodilatation.