[Effect of calcium inhibitors on sympathetic activity]

Interference with the function of the sympathetic nervous system is one of the possible mechanisms whereby calcium-antagonists may lower blood pressure. We have studied the effects of one of those drugs (verapamil) on blood pressure and basal levels of catecholamines. The hypotensive response appeared to be associated with a small insignificant rise in noradrenaline and a significant fall in adrenaline. To explore the role of extracellular calcium we infused calcium gluconate before and during treatment with verapamil. Calcium had only little effect on plasma noradrenaline, but markedly stimulated adrenaline. The latter was not affected by verapamil when given intravenously, but clearly blunted after a period of oral treatment with verapamil. Noradrenaline release was enhanced by calcium during administration of verapamil. It is concluded that extracellular calcium may be involved in the secretion of adrenaline and that this requires transmembrane calcium influx. Perhaps a reduction in circulating adrenaline contributes to the blood pressure lowering effects of verapamil.