Effect of beta blockade on plasma catecholamine levels during psychological and exercise stress

The effect of a single oral dose of 50 mg of metoprolol on plasma catecholamine levels was examined in 11 healthy young men. Subjects were studied during baseline at rest, postural challenge, psychological stressors and graded maximal exercise testing. Metoprolol induced significant increases in plasma norepinephrine (NE) levels across most experimental conditions. Metoprolol did not have a consistent effect on plasma epinephrine levels. Because of wide interindividual variation in drug levels, the NE levels in subjects with high drug levels were compared with the NE levels in subjects who had negligible drug levels. NE levels were higher in subjects with higher drug levels.