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At least 127 records · Page 7Linked to original sources
PubMed1964

SOME OBSERVATIONS ON THE PHARMACOLOGY OF ALPHA-METHYLDOPA.

alpha-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 alpha-methyldopa showed no sign of impairment. Contractions of the cat nictitating membrane were reduced but not abolished by alpha-methyldopa. In cats, dogs and rats, pressor responses to noradrenaline were usually slightly increased by alpha-methyldopa. Pressor responses to tyramine were not affected consistently. alpha-Methyldopa, alpha-methyldopamine and alpha-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 alpha-methylnoradrenaline relative to noradrenaline ranged from one-half to one-ninth on various preparations. The results are discussed in relation to the antihypertensive action of alpha-methyldopa.

Animals↗
PubMed1964

THE EFFECTS OF BETHANIDINE ON THE PERIPHERAL CIRCULATION IN MAN.

Bethanidine has been administered intra-arterially and intravenously into normotensive subjects and its effects on the limb blood vessels, arterial blood pressure, vascular sensitivity to noradrenaline and the degree and time course of sympathetic nerve blockade have been studied. The drug caused an initial constriction of hand and forearm vessels which is attributed to release of catechol amines since it is abolished by the prior administration of phenoxybenzamine. The constriction was followed by a sustained vasodilatation lasting between 5 and 20 hr. Sympathetic blockade of hand vessels commenced immediately on infusion and was complete within 1 hr of administration. Recovery occurred in about 5 hr. Sensitivity to intra-arterial noradrenaline was increased within 10 to 15 min of infusion and before sympathetic blockade was complete. Intravenous administration caused a slight rise in blood pressure of supine subjects. Baroreceptor reflex responses of heart and of limb vessels elicited by tilting the subject feet downwards were abolished by bethanidine and postural hypotension occurred. Bethanidine is a potent sympathetic blocking agent in man with properties intermediate between those of bretylium and guanethidine.

Antihypertensive Agents↗