Studies on the water metabolism and renal functions of the Korean
[영문]PartⅠ. Water Metabolism of the Normal Korea Male
Earlier studies conducted in this laboratory by Suh and Hong(1961) indicated that the renal concentrating ability is lower in the Korean as compared to the occidental. These authors as well as others(Hong et al, 1961) demonstrated further that the osmotic composition of urine excreted by the Korean is somewhat unique in that NaCl accounts for nearly 2/3 of the total urine osmolality, suggesting that the salt intake is perhaps greater while the protein intake is less in the Korean than in the occidental. Regardless of whether this suggestion is true or not, it is of considerable interest to see if the above mentioned phenomena in the Koran are associated with any modification in the known pattern of water metabolism. Hence, in this investigation, the typical pattern of water exchange was determined quantitatively in 10 medical students during 3 different seasons, i.e. summer, autumn and winter. Regardless of the season, subjects were maintained on the sam diet, recommended by the Ministry of Health for the Korean, during the four-day
experimental period. The total amount of fluid inkake and output was determined; the former included drinks, water in food and water of oxidation, and the latter included the urine, water in feces and the evaporative water loss. Results may be summarized as follows:
A) The daily water intake was averaged to 3,810 ml of which 1,256 ml. was by drinks, 2,055 ml was contained in food and 500 ml was the water of oxidation.
B) Of the daily water output, the urinary loss was averaged to 1,844 ml. the fecal loss 144 ml and the evaporative loss 1,819 ml.
C) When the amount of caloric intake and the body weight of subjects were considered, the average daily water intake was 1.08 ml/Cal and 67.0 ml/Kg.
D) The above quantitative pattern of water exchange in the Korean remained unchanged through5tout a year.
E) Daily urinary outputs of NaCl and urea-nitrogen were in the order of 20 gm and 10 gm, respectively.
F) The magnitude of daily fluid intake was best correlated to the daily urinary output of NaCl and little to that of urea nitrogen.
G) These results clearly indicated that the daily fluid intake is significantly greater in the Korean as compared to the occidental.
H) Although the underlying reason(s) for this greater fluid intake in the Korean is not clear at present, it is suggested that the greater salt intake as reflected by its greater urinary exeretion is perhaps responsible for this finding.
PartⅡ. Effect of High Protein Diet on Water Metabolism and Renal Functions
In partⅠ of the present investigation, the average water intake is shown to be significantly greater in the Korean as compared to the occidental. Although this fact has been tentatively attributed to the greater salt intake, the possibility exists that this may be in some way related to the lower renal concentrating ability of the Korean. Hence the protein content of the diet was varied and its effects o the water metabolism and various renal functions have been studied in 4 medical students. Experiments were carried out for 3 weeks for each subjects. During the first and third week, the subject was maintained on a typical, Korean low protein diet, and only during the second week a high protein diet was given. During each week, the water exchange was studied for 6 days at the beginning and
the renal function tests were performed on the 7th day. Results obtained may be summarized as follows:
A) The daily water intake was averaged to approximately 3,000 ml of which 39% was by drinks, 49% the water in food and 12% the water of oxidation.
B) Of the daily water output, 53% was urine, 3% was included in the feces and 44% by the evaporation.
C) The daily water intake for a given caloric intake or body weight was still significantly greater in these subjects than in the occidental. Moreover, the quantitative pattern of water exchange was not modified by the changes in the protein content.
D) The urine osmolality as well as the urea concentration increased when the protein intake was augmented. However, the urinary concentrations of Na**+, Cl**- and K**+ were not influenced by the amount of protein intake.
E) When the high protein diet was given, the values of C^^IN, C^^PAH and Curea showed slight increase; the renal concentrating ability as judged by the magnitude of maximal negative free water clearance(T**c m H^^2O) showed a significant increase.
F) From these results, it is evident that the low renal concentrating ability as seen in the normal Korean is most likely due to the low protein intake. However, the greater fluid intake in the Korean is independent of the changes in the renal concentrating ability. On the basis of these facts, it is again suggested that the greater fluid intake in the normal Korean is attributable to the greater salt intake.
G) Possible reasons for the greater salt intake by the Korean are discussed in the light of maintaining normal hemodynamics while living on a low protein diet.