Both phosphate and NH^^3 contribute to determination of the acidity of urine and it is well known that the amount of urinary phosphate is dependent on the amount of dietary protein.
According to recently published papers (Lee et al., 1962; william et al., 1959), Korean are living on a low protein diet, and thus the capacity of urinary concentration and of urea excreation is lower in the Korean than in the Europeans (and N. Americans of European origin), who take a sufficient amount of protein. The effects of low protein intake are such as to make the kidney lower the urea excretion and the capacity of urinary concentration. Low protein intake also changes the pattern of urinary excreation of phosphate and titratable acidity (Such
and Hong, 1961; Kim, 1963).
For these reasons, attempts have been made to investigate the relationship between the low protein intake and the manner of renal excretion of phosphate and titratable acidity, and this report tends to indicate the important role of TmPO^^4 in the nutritionally low protein state.
To determine normal excretion of titratable acidity, phosphate and NH^^3, subjects were selected at random; 20 men among healthy young medical students (A group) and 15 men from psychiatric patients (B group). From checking the 24 hour urine volume, osmolar concentration, amount of phosphate, ammonia, titratable
acidity and C1**- were measured 3 times each. Phosphate concentration was measured in cubital venous blood.
To investigate the effects of protein on the excretion of titratable acidity, on phosphate and ammonia in urine, healthy adult men were chosen. They were given first low protein diets for 4 days and then high protein diets for 5 days. Finally
they took low protein diets for 4 days (a return to the pre-experimental state).
During the whole experimental period, the same environmental factors were provided for the subjects.
Osmolar concentration, amounts of phosphate and of ammonia, including nitrogen and K**+ concentration, were measured in the 24 hour urine. Venous blood was sampled to determine the phosphate concentration.
To determine TmPO^^4, inulin and 0.11M sodium phosphate solution (pH 7.4) were infused into the antecubital vein. First inulin (50mg/kg) and the Na phosphate solution were given at rate of 500ml per 30min as a priming dose. Then a sustaining dose of inulin (32.5mg per min.) and of the Na phosphate solution (500ml/hr) were infused. When equilibrium in the subjects was reached after 30min to 60min, urine and blood samples were taken to measure phosphate and inulin.
Results and Discussion :
(1) Urinary phosphate, titratable acidity and ammonia excretions showed lower values in both A and B groups than in the Europeans. The figures were for group A, 0.61gm/day, 221ml/day and 0.46gm/day, and for group B, 0.32gm/day, 108ml/day, and
0.3gm/day, respectively. Even in the Korean, it was easily concluded that difference in the dietary condition was well reflected in urinary pH which was lowered to 5 or 6. There was no difference in the blood phosphate between the Korean and European data.
(2) With high protein diet the urinary phosphate was 0.98gm/day and titratable acidity was 245ml/day. However with low protein diet, they were 0.84gm/day and 192ml/day, respectively. They apparently decreased, while ammonia excretion and urinary pH showed little change, and blood phosphate was not affected.
(3) The correlations between urinary nitrogen and urinary phosphate and also between urinary nitrogen and titratable acidity were 0.50 and 0.65, showing a linear relationship. However, the correlation between urinary nitrogen and ammonia
excretion was proved not to be linear in functions, showing 0.42.
(4) The mean value of tubular TmPO^^4 was 183μM/min (ranging from 74 to 355 μM/min) and it was concluded to be much higher in Korean than in Europeans.
As stated above, the amount of protein intake is small in Koreans as compared with that of Europeans, with resultant peculiarities in renal function.
This functional peculiarity of the kidney has already been reported by Suh and Hong (1961) and Kim (1963). According to the above investigators, urea reabsorption capacity is lower and urine concentrating ability is also lower in the Korean.
Moreover, high protein diets proved experimentally effective in correcting the altered renal function.
Many investigators have reported a decrease in renal blood flow and in glomerular filtration rate on a low protein diet, but, interestingly enough, these changes are not seen in the Koreans who have conventionally lived on a low protein diet (Suh
and Hong, 1961). The explanation of this fact waits further studies.
This seemingly conflicting fact (the lack of change in glomerular filtration rate on a low protein diet) is important in the consideration of urine acidification processes involved in the Korean. Since both glomerular filtration rate and plasma
phosphate concentration are the same in both races, the amount of filtered phosphate per unit time in the Korean will be close to that of the European.
However the greater TmPO^^4 in the renal tubules of the Korean, where urine acidification predominantly takes place, may lead to lower intratubular phosphate concentration.
On the other hand, as clearly seen in titratable acid excretion data, the production of fixed acid is so low in the Korean that a smaller amount of H**+ will be secreted in the renal tubules. In spite of this, not only is urine pH lowered to 5 or 6, but also urinary NH^^3 excretion is much lower in the Korean. Hence one may suppose that the smaller H**+ secreted may be completely buffered by small amount of phosphates in the distal tubules.
The Korean, who usually lives on a low protein and low fat diet, excretes only a small amount of phosphates and produces simultaneously a low level of fixed acid.
Accordingly urine acidification in the Korean may occur to the same degree as in European without a need for increased NH^^3 secretion. However, as phosphate excretion is small, urine buffer ability is correspondingly weak. Consequently, should acidosis occur with a resultant greater H**+ secretion, a larger amount of
NH^^3 secretion is required for buffering in the Korean than in the European.