Kazuyuki Fujishima

Potentiation of stretch-induced myogenic tone of dog cerebral artery by hemolysate and the inhibitory action of calcium antagonists

Quick stretching of a helical strip of dog basilar artery at a rate of 10 cm/s to 140% of the slack length of the muscle evoked a delayed contraction. A small amount of hemolysate (0.01-0.2 mg/ml as hemoglobin), which increased the basal tone by 10-15% of the maximum contracture produced by 80 mM K+, potentiated the stretch-induced contraction 2- to 3-fold over the control. The enhanced response to stretch was attenuated by removal of the endothelium and was readily suppressed by Ca2+ antagonists such as nisoldipine and other dihydropyridine drugs as well as diltiazem. The hemolysate had no apparent effect on the contraction due to a quick stretch in Ca2+-free medium or on the contractile response of a chemically skinned arterial strip in the relaxing solution. The results suggest that the hemolysate potentiates the contractile response to stretch by promoting the transmembrane supply of Ca2+. The presence of endothelium seems to amplify the vasoconstrictor action of the hemolysate.