Study on some selective β‐adrenoreceptor blocking effects of 1‐(4‐nitrophenyl)‐1‐hydroxy‐2‐methyl isopropylaminoethane (α‐methyl INPEA)

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Abstract
1 . The effect of methyl substitution in the α-carbon position of the ethanolamine side chain of INPEA was investigated on its β-adrenoreceptor blocking activity in the isolated turtle heart and anaesthetized cats. 2 . In the turtle heart preparation, the pA2 value for erythro-α-methyl INPEA was 5·3, as compared with 6·9 for INPEA, while threo-α-methyl INPEA was extremely weak and its pA2 value could not be determined. 3 . In the intact cat experiments, α-methyl INPEA produced a competitive blockade of the peripheral vasodilator effect of isoprenaline in doses ranging from 5 to 20 mg/kg. However, this agent had a minimal effect on the cardiac stimulant effect of the catecholamine. 4 . These results are consistent with the hypothesis that the β-adrenoreceptors comprise a family of nonhomogeneous receptors and a selective blockade of only some, but not all, responses mediated through their activation can be achieved by specific molecular modification of the β-adrenoreceptor blocking agents.

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