Commentary on the reduced urinary noradrenaline excretion following cold stress and exercise in physically trained rats.

Abstract

Urinary catecholamine excretions of rats trained by swimming or running were compared with those of cold-acclimated rats and controls i.e. sedentary warm-acclimated rats. During cold stress the trained rats excreted less noradrenaline (NA) than did controls. In fact rats trained by swimming excreted less NA than did cold-acclimated rats, while rats trained by running excreted about the same amount as did cold-acclimated rats. 2 h of swimming increased the urinary catecholamine (CA) excretion of all groups but trained rats excreted less NA than did controls and cold-acclimated rats, which had excretions of similar magnitude. The NA excretions of the two trained groups never deviated statistically from each other. It is concluded that concerning NA requirement in order to maintain homeostasis, training produces "cross tolerance" to cold stress but cold-acclimation does not produce "cross tolerance" to acute exercise. Furthermore the positive effect of training on NA excretion during the stress of cold or that of acute exercise seems essentially to be an effect of increased locomotor activity as such regardless of the type of training. It is also suggested that increased levels of locomotor activity of the rat may be of importance for seasonal acclimation of the species by increasing its tolerance to cold.