Effects of calcium antagonists on sympathetic nerve activity

The effect of oral treatment with calcium antagonistic drugs on the activity of sympathetic nerves was investigated by studying the uptake and release of 3H-norepinephrine and the residual 3H-content in arteries of spontaneously hypertensive rats. After three to four weeks administration of verapamil, diltiazem or nifedipine, each at two dose levels, the uptake of 3H-norepinephrine was significantly lower than in control animals. Transmural stimulation induced release of 3H-norepinephrine had a tendency to be lower in treated than in untreated rats. Residual 3H in the vessels incubated with 3H-norepinephrine was significantly lower in all but one group of animals than in controls. In previous studies we found that calcium entry blockers in vitro can release norepinephrine from tissues with sympathetic innervation. The results of present experiments suggest that oral administration of verapamil, diltiazem and nifedipine can release norepinephrine and can lead, after a few weeks, to partial depletion of norepinephrine in the vessels.