1. Adrenaline was infused intravenously in nine normal volunteers to plasma concentrations similar to those found after myocardial infarction. This study was undertaken on three occasions after 5 days' treatment with placebo or the β-adrenoceptor antagonists, atenolol or timolol.

2. Adrenaline increased the systolic pressure by 11 mmHg, decreased the diastolic pressure by 14 mmHg, and increased the heart rate by 7 beats/min. These changes were prevented by atenolol. However, after timolol the diastolic pressure rose (+19 mmHg) and heart rate fell (− 8 beats/min).

3. 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.

4. The serum potassium fell from 4.06 to 3.22 mmol/l after adrenaline. Serum potassium fell to a lesser extent to 3.67 mmol/l after atenolol and actually increased to 4.25 mmol/l after timolol. Adrenaline-mediated hypokalaemia appears to result from the stimulation of a β2-adrenoceptor linked to membrane Na+/K+-ATPase causing potassium influx.

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