Mechanism of Reversal of the Vasomotor Effect of Isoprenaline

Abstract

IT has been recently reported that the usual depressor reaction to isoprenaline in the cat can become pressor when large doses (1 mg) are repeatedly administered^1,2. The reversal of the depressor response into a pressor response has been interpreted by Butterworth as being due to block of β-adrenergic receptors by the large dose of isoprenaline, after initial excitation of these receptors². No mechanism has been suggested, however, for this dual action of the drug. Specific block of β-receptors without affecting the α-receptors (responsible for vasoconstriction) would show up as a pressor response to the next injection of isoprenaline².