12 Discussion 



lower total urine output. Our results are expressed in terms of the amount 

 of water reabsorbed from the glomerular filtrate, that is the urine /plasma 

 (U/P) ratio of inulin. A maximum water diuresis was induced by the 

 oral administration of water plus an intravenous infusion of 5 per cent 

 glucose. There were three groups of subjects — young, middle-aged and 

 old. The young group represents nine individuals aged 26-45, the middle- 

 aged group ten subjects from 46-65 years old, and the old group was 

 from 66-90. Under conditions of maximum diuresis the U/P ratio was 

 about 10 for all three groups of subjects. We gave 0-5 m-u./kg. body 

 weight of pitressin, not enough to cause a rise in blood pressure, but there 

 was a marked inhibition of the diuresis. The U/P ratio in the young group 

 increased to 120 within 10 minutes as compared to 75 in the middle-aged 

 and about 40 for the old. After a period of roughly 50 minutes the diur- 

 esis was again re-established in all three groups (Miller, J. II., and Shock, 

 N. W. (1953). J. Geront, 8, 446) (see Shock, Fig. 10, p. 240). 



Heller: In connexion with your results. Prof. Adolph, I should like to 

 clear up a point which has led to some misunderstanding. Some years 

 ago (Heller, H. (1952). J. Endocrin., 8, 214) we were also interested in 

 the response of newborn and infant rats to vasopressin. Our experiments 

 were not suitable for establishing at w hat time after birth the rats first 

 responded to vasopressin. But we could determine by means of inulin 

 U/P ratios, i.e. by the same technique as that used by Dr. Shock in 

 man, at what postnatal age the antidiuretic response to vasopressin 

 became quantitatively comparable to the response of adult animals. 

 We found that this occurred only in rats older than 22 days. I would like 

 to stress this because some workers have misinterpreted these results: 

 they assumed that we had tried to show that a significant inhibition 

 occurred /or the first time after 22 days. I think that one must expect that 

 this datum of around 20 days may change somewhat in the hands of 

 other workers. Clearly a comparison between the antidiuretic responses 

 of adult and infant rats depends on the choice and strictness of appli- 

 cation of the criteria of comparison. But I think that our data agree with 

 some work which Dr. Falk did later (1955. Amer. J. Physiol., 181, 157). 

 She injected nicotine into infant rats and tried to find out at what post- 

 natal age sufficient vasopressin was secreted by the pituitary gland to 

 produce an inhibition of diuresis which would be quantitatively com- 

 parable to that in adult animals. She found that this occurred at about 

 17-22 days after birth. 



Adolph: I think Dr. Falk (1955) got a significant inhibition consider- 

 ably before 17 days. She also injected vasopressin itself, and by the 

 method of collecting the urine which is expelled in response to perineal 

 stimulation in the infant rat, she was able to get significant inhibition in 

 the first week of postnatal life. There is evidence that antidiuretic 

 hormone or something comparable which could inhibit water diuresis 

 was then being put out by the animal. 



Heller: This is precisely the misunderstanding to which I have been 

 referring. Dr. Falk did get responses to nicotine in animals three days 

 after birth, so you are quite right in saying that responses were obtained 

 much earlier than after 20 days of postnatal life. But she also compared 



