Effect of exercise and adrenal insufficiency on urea production in rats.

Experiments on Wistar rats were designed to study the effect of exercise on urea production in the liver of intact and adrenalectomized rats. The urea production rate was assessed by the 14C-urea content in liver tissue after administration of NaH14CO3. In intact rats swimming caused increases in 14C-urea content in the liver compared to the resting concentrations in intact control rats: by 45% after 30 min of swimming carrying an additional load of 10% body mass by, 35% after 3 h of swimming without an additional load and by 103% after 10 h of swimming. Concentrations of urea in liver and blood were elevated simultaneously. The specific activity of 14C-urea did not change significantly as a result of the exercise performed. In adrenalectomized rats the basal rate of urea production was reduced by an insignificant amount, but swimming for 3 h resulted in a decrease in liver 14C-urea (by 24%). The results confirmed the exercise-induced increase in urea production and indicated as essential role for adrenal hormones in this response.