1. Regulation of magnesium balance is poorly understood. However, hypomagnesaemia has been reported in patients in clinical situations where circulating catecholamines are raised including myocardial infarction, cardiac surgery and insulin-induced hypoglycaemia stress tests.

2. The effects of l-adrenaline infusions, sufficient to achieve pathophysiological levels of adrenaline, and of therapeutic intravenous infusions of salbutamol, a β2-agonist, on plasma magnesium, plasma potassium, plasma glucose and plasma insulin levels were studied in a placebo-controlled design in eight normal subjects.

3. Plasma magnesium levels fell significantly during the adrenaline infusion and also during the salbutamol infusion, though more slowly. In a 1 h period of observation after cessation of the infusions no recovery of plasma magnesium levels was seen. Significant falls in plasma potassium levels were also observed during both infusions with spontaneous recovery within 30 min after the infusions.

4. No significant changes in plasma insulin levels occurred with either salbutamol or l-adrenaline compared with control. Plasma glucose levels rose significantly during the adrenaline infusion.

5. The study suggests that both l-adrenaline and salbutamol cause shifts in plasma magnesium which are not mediated by insulin. We propose that intracellular shifts of magnesium occur as a result of β-adrenergic stimulation.

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