The central hypotensive action of amphetamine, ephedrine, phentermine, chlorphentermine and fenfluramine

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Abstract
The influence of amphetamine, ephedrine, phentermine, chlorphentermine and fenfluramine on blood pressure after infusion into the vertebral artery was studied in anaesthetized cats. All drugs lowered blood pressure after infusion into the vertebral artery but showed hypertensive properties upon intravenous administration in the same dosage, although chlorphentermine (i.v.) decreased pressure after a minor initial rise. The hypotensive action of amphetamine was blocked by piperoxan or yohimbine (α-adrenoceptor blocking agents) and by haloperidol which is known to block central adrenoceptors. The hypotensive action of amphetamine was abolished in reserpinized cats and usually a small increase in blood pressure was observed in these animals after infusion of amphetamine in the vertebral artery. The hypotensive action of amphetamine is probably due to the mobilization of noradrenaline in the brain. The results suggest that the drugs show central hypotensive properties probably brought about by stimulation of central α-adrenoceptors, thus causing a decrease in peripheral sympathetic tone. This general principle would also explain the central hypotensive properties of α-methyl- dopa, α-methylnoradrenaline, l-dopa and m-tyrosine.