The Effects of Cardioselective and Non-Selective β-Adrenoceptor Blockade on the Hypokalaemic and Cardiovascular Responses to Adrenomedullary Hormones in Man

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Abstract
Adrenaline [epinephrine] was infused i.v. in nine normal volunteers to plasma concentrations similar to those found after myocardial infarction. This study was undertaken on 3 occasions after 5 days treatment with placebo or the .beta.-adrenoceptor antagonists, atenolol or timolol. Adrenaline increased the systolic pressure by 11 mm Hg, decreased the diastolic pressure by 14 mm Hg, and increased the heart rate by 7 beats/min. These changes were prevented by atenolol. However, after timolol the diastolic pressure rose (+19 mm Hg) and heart rate fell (-8 beats/min). Adrenaline caused the corrected QT interval (QTc) to lengthen (0.36 .+-. 0.02 s to 0.41 .+-. 0.06 s). No significant changes were found in the QTc when subjects were pretreated with atenolol or timolol. The serum K fell from 4.06 to 3.22 mmol/l after adrenaline. Serum K fell to a lesser extent to 3.67 mmol/l after atenolol and actually increased to 4.25 mmol/l after timolol. Adrenaline-mediated hypokalemia appears to result from the stimulation of a .beta.2-adrenoceptor linked to membrane Na+/K+-ATPase causing K influx.