Physiology of the kidney has shown a remarkable progress in past and thus many renal function tests have been designed by various investigators. However, some of these tests are developed rather recently by preclinical investigators and are still impractical from the clinical point of view. As a result, these function tests are not widely applied to the clinical practice and, hence, certain important renal functions are not well established to the date.
Moreover, some renal functions are known to be modified by many factors. For instance, the amount of daily protein intake is known to regulate the renal concentrating ability, which can be reversed upon returning to the usual high protein diet. This observation has a paramount importance to us when one considers
the fact that the majority of Korean people are living on a low protein diet.
In spite of these facts, very little is known about various renal functions of the normal Korean, with the results that it is virtually impossible to critically evaluate the renal functions of patients in the clinical practice. Therefore, this investigation was undertaken to analyze renal function of the Korean as thoroughly as possible by means all the known tests regardless of the clinical applicability. In the final analysis, results were compared with those obtained in other countries and attempts have been made to explain the differences between the Korean and others. The following renal functions were studied in this investigation:
(A) Renal Hemodynamics
(a) Glomerular filtration rate
(b) Renal plasma flow
(c) Filtration fraction
(d) Renal blood flow
(B) Diluting Capacity
(C) Concentrating Capacity
(c) Maximum free-water extraction during mannitol diuresis(T**c m^^(H^^2 O))
(D) Tubular Reabsorptive Capacity of Glucose(Tm^^G)
(E) Tubular Secretory Capacity of PAH(Tm^^PAH)
(F) Tubular Reabsorption of Urea
In total, 46 healthy Koreans (42 males and 4 females) whose age ranged from 18 to 37 years old wereused in this investigation.
In most tests, both inulin and PAH clearnaces were routinely determained as measures of the glomerular filtation rate(GFR) and the renal plasma flow (RPF), respectively. All the numerical figures indicating various renal functions were recalculated for the body surface area of 1.73㎡ and the values of standard
deviation were also calculated in order that these values can be compared with those reported in other countries.
Results obtained from various function tests may be briefly summarized as follows:
(A) Renal Hemodynamics:
(a) Glomerular filtration rate: In 37 subjects, the inulin clearance was measured in order to determine the glomerular filtration rate. A priming dose of 50㎎ of inulin per ㎏ was infected intravenously, followed by a sustaining dose of 32.5㎎ per min. The average inulin clearance was 117±21.9㏄/min.
(b) Renal plasma flow: In 25 subjects, the PAH clearance was measured for the determination of renal plasma flow. As a priming dose, 8㎎ of PAH per ㎏ was injected intravenously, followed by a sustaining dose of 12㎎ per min during the experimental period. The average PAH clearance was 706±149.5㏄/min.
(c) Filtratin fraction : As calculated from the above results, the filtration fraction was averaged to be 0.17±0.037.
(d) Renal blood flow. The hematocrit ratio was determined in 8 subjects along with the PAH clearance, in order to calculate the renal blood flow(RBF). The calculated renal blood flow was 1133±85㏄/min.
(B) Diluting Capacity: In 6 subjects, 1000㏄ of water was initially given following which the amount of water excreted in urine was replaced during the experimental period. During maximum water diuresis, the urine osmolarity and the urinary concentration of chloride were averaged to 105±12.5 mOsm/L and 26±7.0 mEq/L, respectively, whereas the maximal urine flow and the osmolar clearance were averaged to be 20.0±3.7 and 6.8±1.6㏄/min, respectively, with the result that the positive free-water clearance(C^^(H^^2 O)) was claculated to be 13.2±2.2㏄/min.
(C) Concentrating Capacity
(a) ADH-induced: In 4 hydrated subjecs, a priming dose of 200 mu of pitressin was given intravenously following which a sustaining dose of 4 mu per min was infused throughout the entire experimental period. At the peak of maximum antidiuresis, the urine osmolarity and urinary concentration of chloride were
averaged to 630±146mOsm/L and 210±64mEq/L, respectively; the average negative free-water clearance(T**c(H^^2 O) was 3.2±0.6㏄/min.
(b) Dehydration-induced: In 8 subjects(4 males and 4 females), the water intake was completely prohibitited for at last 12 hours prior to the experiment during which samples of the maximally concentrated urine as well as plasma samples were obtained. The plasma osmolarity and the chloride concentration of plasma were averaged to be 304±24.3mOsm/L and 112±7.6mEq/L, respectively, whereas the urine osmolarity and the chloride concentration of urine were averaged to be
1172±266mOsm/L and 312±84.8mEq/L, respectively. The average urine flow and the osmolar clearance were 0.35±0.05㏄/min and 1.2±0.67㏄/min, respectively, with the result that the negative free-water clearance T**c m^^(H^^2O)) was 0.89±0.47㏄/min. The U/P osmolar ratio was, on the average, 3.84±0.83.
(c) Maximum free-water extraction during mannitol diuresis(T**c m^^(H^^2O)): In 5 subjects, a priming dose of 200 mu of pitressin was given intravenously following which 4 mu of pitressin per minute was constantly infused during the entire
experimental period, while 20% mannitol solution was infused as rapidly as possible. During the maximum urine flow, the urine osmolarity was 448±54mOsm/L and calculated T**c m^^(H^^2 O)) was 4.2±1.3㏄/min.
(D) Tubular peabsorptive Capacity of Hlucose(Tm^^G) : In 5 subjects, a priming dose of 125 gm of dextrose in 50% solution was given intravenously, followed by a sustaining dose of 2 gm/min, in order to raise the plasma level of glucose. The average plasma level of glucose was 623±160mg% while the calculated Tm^^G was 280±41.1 mg/min
(E) Tubular Secretory Capacity of PAH(Tm^^PAH) : In 5 subjects, a priming dose of 160 mg of PAH per kg was given intravenously, followed by a sustaining dose of 120 mg/min. The plasma concentration of PAH was maintained, on the average, at the
level of 30.2±12.3 mg% and the calculated Tm^^PAH was 93±25.8 mg/min.
(F) Tubular Reabsorption of Urea : In 6 subjects, the average urea clearance was 51.6±9.5 cc/min which was equivalent to 0.399±0.061 of the inulin clearance.
When the above described results obtained from the normal Korean are compared with those reported in other countries, the following conclusions may be drawn:
(A) Although the value of GFR was somewhat lower while RPF was somewhat higher in the Korean as compared to the corresponding values reported in the U.S.A., there was no statistical significance. Therefore the filtration fraction was also nearly
identical in both groups. The calculated value of RBF was also similar to others.
(B) The diluting capacity, as may be clearly defined by the value of positive free-water clearance, was not significantly different from others.
(C) Both ADH-induced and dehydration-induced concentrating capacities tended to lower in the Korean as compared to others reported in the U.S.A. and England. The maximum free-water extraction (T**c m H^^2 O) was also less in the Korean than
others. Furthermore, the urinary concentration of NaCl, as estimated by multiplying the chloride concentration by 2, accounted for approximately 2/3 of the total urinary osmotic constituent in the Korean while it is less than 1/2 in others. As
will be mentioned below, this is due to the fact that the urea reabsorption is greater in the Korean than others.
(D) Tm^^G was lower in the Korean than that reported in the U.S.A.
(E) Although Tm^^PAH tended to be higher in the Korean than that in the U.S.A., there was no significant difference.
(F) When the urea/inulin clearance ratio was analyzed as a function of urine, plasma inulin concentration ratio, there was a distinct tendency for the former to be lower in the Korean than that in the U.S.A.
In summary, may be emphasized that certain renal functions of the Korean are not indentical to those reported in the literature, but ar similar to those which are seen upon feeding a low protein diet. The fact that Korean people are living on a
low protein diet may have an important nearing in bringing about unique renal functions in the normal Korean.