Exercise-induced hyperkalaemia: effects of beta-adrenoceptor blocker vs diuretic.

Four groups of eight normotensive male volunteers performed a 60 min bicycle exercise test before and after 2 weeks of either placebo, hydrochlorothiazide (HCTZ, 25 mg day-1), pindolol (PIND, 10 mg day-1) or both drugs in combination using a double-blind, randomized design. During exercise on placebo serum potassium increased by 0.8 mmol l-1. HCTZ significantly decreased potassium levels at rest and during exercise by 0.2 mmol l-1. PIND did not affect resting potassium levels but potentiated the increase by 0.4 mmol l-1 at the end of exercise, and delayed the return to normal of serum potassium after exercise. The addition of HCTZ to PIND offset the potentiating effect of PIND on exercise-induced hyperkalaemia (only after prolonged exercise) and accelerated the return to baseline after exercise. The results indicate that the hypokalaemic effect of HCTZ can oppose the hyperkalaemic effect of PIND during prolonged physical exercise and particularly during recovery.