Pharmacological Properties of Hydrallazine, Dihydrallazine and Some Related Compounds

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Abstract
Hydrallazine and dihydrallazine cause adrenaline reversal and antagonise the pressor effects of noradrenaline on the cat blood pressure. Both hydrallazine and dihydrallazine antagonise vasoconstriction caused by adrenaline, noradrenaline, histamine, 5-hydroxytryptamine or barium chloride in isolated perfused preparations of the rat hind quarters or rabbit ear. In isolated aortic strips antagonism is shown to the constrictor action of adrenaline, noradrenaline, histamine and 5-hydroxytryptamine but not to barium chloride. Marked antagonism to 5-hydroxytryptamine is shown only on the perfused rat hind quarters or rabbit ear. Antagonism to pressor reflexes is of moderate potency or is absent. Applied locally to the carotid sinuses of the cat, hydrallazine causes a rise of blood pressure. Hydrallazine and dihydrallazine have mainly a peripheral site of action involving an effect upon the contractile elements of the blood vessel walls. 3-Phenyl-6-hydrazino-pyridazine HCl, 1-hydrazinoisoquinoline HCl and 3:6-dihydrazino-pyridazine nitrate appear to have similar properties to hydrallazine and dihydrallazine.
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