Swimming capacity of mice after prolonged treatment with psychostimulants. I. Effects of caffeine on swimming performance and cold stress.

A comparative study of the effects of a single dose of caffeine (50 microgram/g s.c.) and of 6-weeks treatment with 150 microgram/g p.o. caffeine/day on swimming capacity and resistance to cold exposure was performed in mice. In contrast to acute treatment, chronic treatment with caffeine greatly reduced the swimming capacity and diminished the ability of the animals to withstand cold stress. It could be shown by indirect means that the detrimental effect of the prolonged treatment with caffeine was not due to an accumulation of toxic levels of caffeine. Motor coordination was unaffected. There was no deficiency of metabolic substrates, since glycogen, and fat stores, and blood glucose, and fatty acid levels were not lower than in control animals. It is proposed that caffeine may interfere with the animals' ability to mobilize and spend metabolic substrates for energy requirements of skeletal muscle.