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

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.

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

“…Rats trained by running excreted significantly less NA during rest than did controls and coldacclimated rats. In a previous study (Ostman & Sjostrand 1975) cold-acclimated rats and rats trained by swimming were found to excrete significantly less NA during resting conditions than did sedentary warm-acclimated rats. All groups showed significantly increased NA-excretions in the urine collected after exercise, when compared with the corresponding values obtained during the resting state (increase in per cent: controls= 44; coldacclimated rats = 60; trained rats I = 22; trained rats I1 = 28).…”

“…The sampling of resting CA-excretion was preceded by 2-3 days of rest in the case of the trained rats and by 3-4 days at 2426°C in the case of the cold-acclimated rats. The same periods of rest and exposure to room-temperature preceded the 2 h ofswimming to which the rats were subjected before urine collection ufrer exercise started (Ostman & Sjostrand 1975). Urine collection during cold stress was performed after 15-19 weeks of training or cold-acclimation, respectively.…”

Renal Responses to Bicycle Exercise in Trained Athletes: Influence of Exercise Intensity

“…Changes in renal function during exercise are generally considered as secondary to the effect of the activity of the sympathetic nervous system on renal blood flow (8). Sympathetic nervous activity, as reflected by plasma norepinephrine, has been shown to be related to the intensity of work (6) and to be affected by previous training (10). Furthermore, renal blood flow has been found to be reduced during alarm, conflict or other behavioral conditions (7).…”