248 Discussion 



individual in the renal series was able to concentrate his urine at least 

 to a specific gravity of 1 • 020 on a Fishberg routine. However, Lewis and 

 Alving (1938. Amer. J. Physiol., 123, 500) have published blood urea 

 levels in 100 subjects aged 20 to 80. They found little increment in 

 blood urea up to the age of about 70, but from 70 on it does increase in 

 their data. 



I must make it clear that the increment in Tm following lactate infu- 

 sion occurs only during the time that the blood lactate level is raised. We 

 have not been able to show that it induced any kind of renal hypertrophy. 



Fejfar: I would not expect the blood urea level to increase, because in 

 a paper on chronic nephritis, Brod (1948. Cas. Lek. des., 87, 711) showed 

 that the blood urea did not rise markedly in patients with low protein 

 intake unless the glomerular filtration rate decreased to less than 25-30 

 ml./min.; in your work the glomerular filtration rate was far above this 

 figure. 



In congestive failure or other situations where cardiac output is inade- 

 quate, there is usually a decrease in renal blood flow, and an increase in 

 tubular reabsorption of water. The normal concentration test might 

 point to a diversion of blood from the kidneys due to this insufficient 

 cardiac output. 



Shock : I did not perhaps make it clear that unfortunately we only got 

 the cardiac output method in operation rather late in the series, so that 

 the cardiac output results that I showed you in the average curve were 

 not determined on the same subjects as the renal functions. We are now 

 measuring cardiac output and renal function in the same subjects simul- 

 taneously. The crucial point to me is whether there is a change in the 

 percentage of cardiac output that gets through the kidney, and I just 

 cannot answer that at the moment. 



Milne: I have some difficulty about this fall in glomerular filtration 

 rate without a rise in blood urea with advancing age. It seems to me that 

 this could only be possible if the older people were not taking in so much 

 protein, or if the urea back-diffusion was diminishing and therefore the 

 clearance of urea was approaching the inulin clearance. I should have 

 thought that a fall in glomerular filtration rate of this magnitude would 

 necessitate a rise in blood urea, although it might not of course go above 

 some arbitrary upper limit of normal such as 40 mg./lOO ml. 



Black: My question on blood urea really referred to blood urea in a 

 population and not in an individual. I think Van Slyke showed that in 

 terms of a population, even with 80 per cent of normal urea clearance 

 there is a detectable increase in the blood urea. All our clinical experi- 

 ence is that the glomerular filtration can be down to 30 per cent without 

 the blood urea being outside the so-called normal range in that individual 

 but if you do it in a population you then find that even with an 80 per 

 cent clearance the level is raised. 



Borst: Dr. Shock, you eliminated all diseased people, but at what 

 blood pressure was a man eliminated as not having normal kidneys? 



Shock : We excluded anyone who had a systolic pressure greater than 

 160 and a diastolic greater than 90 mm. Hg. Prof. Olbrich (Olbrich et 

 al. (1950). Edinh. med. J., 57, 117) was doing similar renal functional 



