172 JiM Krecek, et al, 



kidney parenchyma or to the fact that from the end of the 

 fourth week a regulatory factor is present which can be 

 influenced by loading the organism with water. It therefore 

 seemed all the more interesting to us to find out whether the 

 function of the adrenals changes at the time of weaning. 



After adrenalectomy the ability to eliminate a water load is 

 strongly reduced in infant rats. It is difficult therefore to use 

 this method for solving the problem. A less direct way was 

 chosen — a study of the effect of substances that act in a 

 similar way to the main corticoids. Cortisone or cortexone 

 was administered for six days in various doses to 18-23 and 

 28-33-day-old animals. Then a water load was given. It 

 appeared that the effect of these substances also depends on 

 the age of the rats. 



The effect of cortisone is shown in Fig. 2. The elimination 

 of a water load, sodium and potassium was determined in rats 

 that received 0-125, 0-25 or 0-5 mg. cortisone/100 g. body 

 weight. The hormone has opposite effects in the younger 

 and in the older age groups. In 23-day-old animals it increases 

 the excretion of water (as it does in the 3-day-old rats of 

 Falk, 1955) and sodium, while in the 33-day-old rats it 

 decreases both. After a dose of • 25 mg./lOO g. body weight, 

 renal water and sodium losses in the younger animals reach 

 approximately the levels of the older control animals. It 

 appears as if the administration of cortisone compensates for 

 a factor missing in the younger animals but present in the 

 older rats. This, however, is not borne out by the way in 

 which a water load is eliminated by the younger rats after 

 cortisone. Fig. 3 shows changes in the concentration of 

 sodium in the urine during the course of water diuresis in 

 normal animals and after cortisone (0-25 mg./lOO g.). In the 

 control 33-day-old animals the concentration rises as the in- 

 tensity of water diuresis falls. In the younger group there is no 

 such relationship and the concentration is not lowest during 

 the highest diuresis. If cortisone were only a substituting 

 substance the course of the curves of sodium concentration 

 ought to be the same in 23-day-old rats receiving cortisone 



