EFFECTS OF EXOGENOUS CATECHOLAMINES AND EXERCISE ON PLASMA MAGNESIUM CONCENTRATIONS

Abstract

Catecholamines and physical exercise are known to influence the metabolism of several minerals in man, but the effects on magnesium (Mg) have been scarcely investigated. In the present study, infusion of adrenaline (5 .mu.g/min for 30 min followed by 10 .mu.g/min for 30 minutes) significantly reduced the plasma Mg levels in healthy males. This effect was abolished by simultaneous infusion of propranolol. Noradrenaline had no such effect. In order to stimulate endogenous catecholamine release healthy males carried out physical exercise in four different ways: (1) ergometer bicylcing at maximum load until exhaustion with and without oral beta-blockade, (2) ergometer bicycling with stepwise increasing load until exhaustion, (3) isokinetic maximal exercise with one leg, with blood sampling both from the venous effluent of the exercising leg and the opposite resting arm and (4) long-term (60 min) steady state ergometer bicycling at approximately 65% of estimated maximum capacity. During short-term (less than 20 min) intense exercise (i.e. experiments 1-3) the plasma Mg concentrations were increased. This was probably due to a reduction of plasma volume and to an influx of Mg to the vascular pool. During long-term steady state exercise (experiment 4) the Mg levels were not significantly affected but decreased during the first hour of recovery. These results suggest that both the beta-adrenergic system and muscular activity by itself affect Mg homoestasis.