Effects of calcium antagonists on myogenic and neurogenic control of resistance and capacitance vessels in cat skeletal muscle

The effects of five different calcium antagonists (diltiazem, felodipine, nifedipine, nimodipine, and verapamil) on cat skeletal muscle resistance and capacitance vessels were studied in a whole organ preparation. These calcium antagonists seemed to have the similar qualitative effects on these vascular functions. Calcium antagonists were found to be potent inhibitors of myogenic vascular reactivity (here defined as the maximal increase in flow resistance evoked by a sudden rise of transmural pressure). Basal vascular tone and vascular tone induced by low frequency stimulation of sympathetic nerves were both less sensitive to these drugs than vascular tone induced by myogenic vascular reactivity. Sympathetically mediated vascular tone at high stimulation frequencies seemed to be least sensitive. Further, resistance vessels were much more sensitive to these drugs than capacitance vessels. Finally, basal tone in the large bore arterioles were more sensitive than in the small bore arterioles, a surprising finding which was interpreted with the aid of computer simulations using a mathematical model of local vascular control in cat skeletal muscle. The model suggested that this difference could be due to a delicate interaction between myogenic vascular reactivity and metabolic vascular control. It is suggested that the inhibition of myogenic vascular reactivity is a factor contributing to the edema formation of calcium antagonists.