Reduced Urinary Noradrenaline Excretion during Rest, Exercise and Cold Stress in Trained Rats: a Comparison between Physically-Trained Rats, Cold-Acclimated Rats and Warm-Acclimated Rats

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Abstract
Physically trained rats were compared with cold-acclimated rats. Trained as well as cold-acclimated rats showed cardiac and adrenal hypertrophy. Cardiac noradrenaline (NA) content was increased in both groups of rats but only the trained rats had an increased cardiac NA concentration. The adrenal NA content was increased in both groups but only the trained rats had an increased adrenal content of adrenaline (A). The spleen of trained rats had an increased NA content, while that of cold-acclimated rats had a decreased NA content. The submandibular glands of cold-acclimated rats were enlarged and had an increased NA content. Trained as well as cold-acclimated rats had lower urinary NA excretions during rest, after exercise and during cold stress when compared with controls. However, only the trained rats had a reduced net increment in NA excretion after exercise, whereas there was no difference between the increments of cold-acclimated and control rats. Six months after cessation of training, ex-trained rats still had an increased heart ratio and a reduced urinary NA excretion after exercise. It is suggested that physical training induces "cross tolerance" to cold stress, while cold-acclimation does not lead to "cross tolerance" to acute exercise.