EFFECT OF HYDRAZINOPHTHALAZINES ON CATECHOLAMINES IN RATS

The actions of hydralazine and dihydralazine on the noradrenaline content of the heart, adrenals and brain were investigated in rats. Both drugs decreased the concentration of bound dl-7-3H-noradrenaline in the rat heart. The only significant change in the endogenous catecholamine content of tissues after the drugs were given twice daily for two days was observed in the hearts of rats treated with dihydralazine. After a single injection of dihydralazine, the endogenous noradrenaline content of the heart decreased, the lowest concentration being reached after 4 hours, and then returned rapidly to normal levels 6 hours after the administration of the drug. The repeated administration of dihydralazine to rats which had received tritium-labelled noradrenaline, led to a decrease in the specific activity of the cardiac noradrenaline in the treated groups as compared with the controls. the depletion of cardiac noradrenaline is interpreted as the consequence of an increased activity of the sympathetic cardiac nerves, triggered off by the decrease in the peripheral vascular resistance. © 1969.