SOME OBSERVATIONS ON THE PHARMACOLOGY OF α‐METHYLDOPA

Abstract

α-Methyldopa in high concentrations impaired the responses of rabbit isolated ileum and guinea-pig isolated vas deferens to stimulation of the sympathetic nerves and to noradrenaline, but these preparations taken from animals previously treated with α-methyldopa showed no sign of impairment. Contractions of the cat nictitating membrane were reduced but not abolished by α-methyldopa. In cats, dogs and rats, pressor responses to noradrenaline were usually slightly increased by α-methyldopa. Pressor responses to tyramine were not affected consistently. α-Methyldopa, α-methyldopamine and α-methylnoradrenaline behaved like dopa, dopamine and noradrenaline respectively in restoring the responses of tissues from reserpine-treated animals to stimulation of the sympathetic nerves to the rabbit ileum, the guinea-pig vas deferens and the cat nictitating membrane and in restoring responses to tyramine of the cat blood pressure and nictitating membrane, and the rat blood pressure. The potency of α-methylnoradrenaline relative to noradrenaline ranged from one-half to one-ninth on various preparations. The results are discussed in relation to the anti-hypertensive action of α-methyldopa.