Effect of Acetyl Derivatives of some Sympathomimetic Amines on the Blood Pressure of the Rat

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Abstract
The effect of 5 sympathomimetic amines and some of their acetyl derivatives on the blood pressure of the rat was determined on the left carotid artery. After chlorisondamine (1 mg/kg s.c.) pretreatment the blood pressure rise by sympathomimetic amines and their acetyl derivatives was compared with that of adrenaline. If the potency of adrenaline is specified as 100, the potencies of the other drugs are phenylephrine (metaoxedrinum, NFN) 37, tyramine 1.1, O-acetyltyramine 0.52, amphetamine 0.50, O-diacetylphenylephrine 0.25, ephedrine 0.23, O-acetylephedrine 0.02, N-acetylphenylephrine 0.01. The effects of N-acetyltyramine, N-acetylephedrine and N-acetylamphetamine are even weaker. Reserpine (5.0 or 0.05 mg/kg, i.p.) 24 h before the experiment increased the blood pressure rise by directly acting sympathomimetic amines and their acetyl derivatives, but decreased the effects of indirectly acting drugs. After phenoxybenzamine (2 mg/kg i.p.), adrenaline exhibited the greatest blood pressure decrease and the effects of the other drugs in descending order: orciprenaline, O-acetyltyramine, phenylephrine, ephedrine, amphetamine, O-diacetylphenylephrine and O-acetylephedrine. Tyramine showed no blood pressure decrease. The blood pressure decrease by sympathomimetic amines and by their acetyl derivatives was probably due to .beta.-receptor stimulation since this response was prevented by propranolol. The N-acetyl derivatives resembled their parent drugs with regard to the immediate onset and short duration of their effects. The O-acetyl derivatives exhibited slower onset and longer duration of effect than their parent drugs. Physostigmine-pretreatment diminished the rise in blood pressure by O-acetyltyramine, but the effect of tyramine remained unchanged.