Aims: Like potassium (K+), caesium (Cs+) tends to concentrate intracellularly. The aim here was to determine how moderate exercise affects the uptake of Cs+ from blood plasma.
Methods: After an intravenous Cs+ dose of 5 micromol kg(-1), plasma Cs+ concentration was followed for 100 min in goats and for 60 min in horses. The latter were divided into two groups, one resting and the other trotting on a treadmill (inclination 3 degrees, speed 5 m s(-1)).
Results: The plasma Cs+ concentration follows a multiphase exponential decay curve, which initially could be approximated with a two-phase curve. The initially high rate constant (approximately 10 h(-1)) decreased to around 1 h(-1) in 40 min. Exercise more than doubled the rate of removal of Cs+ from plasma between 20 and 40 min after the start of exercise. After exercise, the rate returned to resting levels within 10 min. Plasma K+, on the contrary, declined for at least 20 min after exercise had ended.
Conclusions: Moderate exercise significantly increases the rate of removal of Cs+ from the bloodstream. After exercise, the rate returns to the resting levels within 10 min. The increased rate of Cs+ removal during exercise is likely due to increased activity of Na+, K+-ATPase in working skeletal muscles.