[Kidney function in calves in the neonatal period. II. Studies of the capacity to reduce and increase urine concentration].

Examinations were made with the use of same materials as in Part I and according to the same methodology. The great capability of the calves kidneys to economise water was observed. The kidneys are able already in the second week of calves life to reduce and increase urine concentration within limits from 65.70 to 955.54 mmol/kg H2O, keeping at the same time molality of the body fluids on relatively the same level. It may prove high efficiency of the hypothalamic pituitary antidiuretic system. It seems, that because of the probable immaturity of tubules it was difficult to create the high osmotic gradient in the renal medulla what is confirmed by the changing clearances of the free water and the resorption water. It also seems, that the rate with which urine is passing through the renal tubules is of great importance in the process of thickening the urine in this period.