Renal urea clearance in normal and adrenalectomized rats after exercise.

In groups of male Wistar rats, blood level, urinary excretion of urea, and renal urea clearance were determined in resting conditions or during 48-60 h after swimming for 30 min with an additional load of 10% of body weight as well as after swimming for 3 or 10 h without additional load. Both types of swimming exercise caused a significant increase in the blood level, urinary excretion, and renal clearance of urea. After 10-h swimming, the increase of renal urea clearance was observed only from the second period (0-12 h) of urine collection. In this type of exercise, an elevation of blood level of corticosterone was obtained after 6-h restitution. The increased urinary excretion and renal urea clearance persisted for a longer time than was necessary for the normalization of the blood level. A significant rise in blood urea level and a drop in renal urea clearance occurred after adrenalectomy. In adrenalectomized rats, increased urea excretion and renal clearance were observed 12-24 h after 3-h swimming, but the level of renal clearance obtained in sedentary normal rats was not achieved. The blood level of urea did not increase. This suggested that the glucocorticoids play a role both in urea formation during exercise and in its elevated renal clearance after exercise.