단백질과 식염(食鹽)섭취량과의 상관성 및 이들이 신(腎)기능에 미치는 영향

Abstract

[한글]

Interrelationship Between Sodium Chloride and Protein Intake and Its Effect on

Renal Function

Won Chul Choe

Department of Physiology, Yonsei University College of Medicine, Seoul, Korea

(Directed by Drs. P.H. Lee, S.K. Hong and K.Y. Lee)

It has teen widely established that the Korean ingest large amounts of sodium

chloride, while living on a low protein diet(Lee et al., 1962; Kim, 1963; Hong et

at., 1961). As a result of this high salt and low protein diet, certain renal

functions of the Korean are known to be different from those of the occidental(Hong

et al., 1961; Suh, 1961; Kim, 1773; Chang, 1965). In a series of investigations

regarding this problem, Kim (1963) speculated earlier that a high salt intake by

the Korean is perhaps attributable to the ingestion of a l7w Protein diet. In fact,

Lee (1965) showed in his extensive studies on the daily excretion of Na, K and

nitrogen in the Korean that the salt intake is an inverse function of the protein

intake. However, quantitative studies on the interrelationship between salt and

protein intake have never been reported in the literature. Hence, this

investigation was undertaken to study in the rat a Quantitative interrelationship

between the salt and the protein intake. In addition, attempts have been also male

to study the electrolyte and urea concentration Profiles of the renal medulla in

these rats, in order that one can evaluate the renal concentrating operation under

various dietary conditions.

104 immediately weaned albino rats(Sprague-Dawley strain), weighing about 25 gm.

were used. They were divided into four different dietary groups according to the

content of salt and protein in their basal diet:

Group Ⅰ-high protein diet(50% casein in diet)

Group Ⅱ-low protein diet (6% casein in diet)

Group Ⅲ-high salt diet(1.6% NaCl in diet)

Group Ⅳ-low salt diet(0.03% NaCl in diet)

All rats were provided with tap water and the assigned diet ad libitum. In

addition, 5% NaCl solution for the Groups Ⅰ and Ⅱ, and casein for the Groups Ⅲ

and Ⅳ were provided ad libitum. The experiment was carried out for 4 months during

which the body weight, the food intake, the water consumption, and the urine

osmolarity were determined. At the end of 4 months, a blood sample was collected

from each rat under light ether anesthesia from the femoral artery for the analysis

of plasma Na and K. The rats were then sacrificed and the intestine, the kidney,

the adrenal glands, the heart and the liver were removed for the determination of

weight. In addition, the electrolytes and urea concentrations of the various

segments of the renal medulla were also determined.

The results may be briefly summarized as follows:

(1) The Group Ⅰ ingested approximately 7 times more casein than the Group Ⅱ,

while the Group Ⅲ ingested approximately 60 times more salt than time Group Ⅳ.

(2) The growth rate was greatest in the Group Ⅰ and was significantly greater

than the rest of groups (p<0.05) , The growth rate of Groups Ⅱ, Ⅲ and Ⅳ showed

no significant difference, although the Group Ⅱ showed somewhat a Bower growth

rate than time other two groups.

(3) The daily fond intake was greater in the Group Ⅱ than in the Group Ⅰ,

whereas it was greater in the Groups Ⅲ and Ⅳ than in the Groups Ⅰ and Ⅱ.

However, there was no difference in the amount of food intake between the Groups Ⅲ

and Ⅳ, On the other hand, the daily water intake was closely related to the salt

intake.

(4) The salt intake was significantly greater in the Group Ⅱ than in the Group

Ⅰ (p <0.05). However, there was no significant difference in the casein intake

between the Groups Ⅲ and Ⅳ.

(5) The weights of the kidney and the liver were smallest in the Group Ⅱ while

the weights of the heart, the spleen and the adrenal glands were not different

among 4 groups

(6) In general, the tissue concentrations of Na and urea in the kidney were

lowest in the cortex and increased progressively toward the papilla. However, the

papillary concentration of Na was highest in the Group Ⅲ while that of urea was

highest in the Group Ⅰ.

(7) The papillary urea concentrations were proportional to the urine osmolarity.

The papillary Na concentration also linearly increased as a function of the urine

osmolarity until the Na concentration reached a level of 350 mEq/kg tissue water

after which there has no further increase in Na. In other words, the renal

concentrating operation seems to be carried out by two me chanisms: the first by

increasing the concentrations of both Na and urea in the renal medulla until the

former reaches a maximum, and the second by increasing the urea concentration only.

(8) The tissue concentration of K in the kidney was highest in the cortex and

decreased progressively toward the papilla. Moreover, the tissue concentration of K

at a given portion of the kidney was not different among 4 groups.

These results indicate that the amount of protein intake seems to determine the

amount of salt intake while the amount of salt intake does not regulate the amount

of protein intake. This finding consistent with the view speculated earlier by Kim

(1963) and may have an important bearing on the dietary habit of the people who are

usually living on a low protein diet, However, the underlying mechanism for this

interrelationship between the protein and the salt intake is yet to be studied. It

is also clear from this investigation that the enhancement of renal concentrating

operation in the high protein dietary group is attributable to the ability to

concentrate urea in the renal

medulla. Although both Na and urea are the mast important determinants of the

medullary osmotic gradient, the renal medulla can not concentrate Na beyond a

certain level. On the other hand, urea can be concentrated in the renal medulla

without showing any maxim71 level whereby providing additional amounts of solute to

the renal medulla for further water reabsorption in the collecting duct.

[영문]

It has teen widely established that the Korean ingest large amounts of sodium chloride, while living on a low protein diet(Lee et al., 1962; Kim, 1963; Hong et at., 1961). As a result of this high salt and low protein diet, certain renal functions of the Korean are known to be different from those of the occidental(Hong et al., 1961; Suh, 1961; Kim, 1773; Chang, 1965). In a series of investigations regarding this problem, Kim (1963) speculated earlier that a high salt intake by the Korean is perhaps attributable to the ingestion of a l7w Protein diet. In fact, Lee (1965) showed in his extensive studies on the daily excretion of Na, K and nitrogen in the Korean that the salt intake is an inverse function of the protein intake. However, quantitative studies on the interrelationship between salt and

protein intake have never been reported in the literature. Hence, this investigation was undertaken to study in the rat a Quantitative interrelationship between the salt and the protein intake. In addition, attempts have been also male to study the electrolyte and urea concentration Profiles of the renal medulla in these rats, in order that one can evaluate the renal concentrating operation under various dietary conditions.

104 immediately weaned albino rats(Sprague-Dawley strain), weighing about 25 gm. were used. They were divided into four different dietary groups according to the content of salt and protein in their basal diet:

Group Ⅰ-high protein diet(50% casein in diet)

Group Ⅱ-low protein diet (6% casein in diet)

Group Ⅲ-high salt diet(1.6% NaCl in diet)

Group Ⅳ-low salt diet(0.03% NaCl in diet)

All rats were provided with tap water and the assigned diet ad libitum. In addition, 5% NaCl solution for the Groups Ⅰ and Ⅱ, and casein for the Groups Ⅲ and Ⅳ were provided ad libitum. The experiment was carried out for 4 months during which the body weight, the food intake, the water consumption, and the urine

osmolarity were determined. At the end of 4 months, a blood sample was collected from each rat under light ether anesthesia from the femoral artery for the analysis of plasma Na and K. The rats were then sacrificed and the intestine, the kidney, the adrenal glands, the heart and the liver were removed for the determination of weight. In addition, the electrolytes and urea concentrations of the various segments of the renal medulla were also determined.

The results may be briefly summarized as follows:

(1) The Group Ⅰ ingested approximately 7 times more casein than the Group Ⅱ, while the Group Ⅲ ingested approximately 60 times more salt than time Group Ⅳ.

(2) The growth rate was greatest in the Group Ⅰ and was significantly greater than the rest of groups (p<0.05) , The growth rate of Groups Ⅱ, Ⅲ and Ⅳ showed no significant difference, although the Group Ⅱ showed somewhat a Bower growth

rate than time other two groups.

(3) The daily fond intake was greater in the Group Ⅱ than in the Group Ⅰ, whereas it was greater in the Groups Ⅲ and Ⅳ than in the Groups Ⅰ and Ⅱ.

However, there was no difference in the amount of food intake between the Groups Ⅲ and Ⅳ, On the other hand, the daily water intake was closely related to the salt intake.

(4) The salt intake was significantly greater in the Group Ⅱ than in the Group Ⅰ (p <0.05). However, there was no significant difference in the casein intake between the Groups Ⅲ and Ⅳ.

(5) The weights of the kidney and the liver were smallest in the Group Ⅱ while the weights of the heart, the spleen and the adrenal glands were not different among 4 groups

(6) In general, the tissue concentrations of Na and urea in the kidney were lowest in the cortex and increased progressively toward the papilla. However, the papillary concentration of Na was highest in the Group Ⅲ while that of urea was highest in the Group Ⅰ.

(7) The papillary urea concentrations were proportional to the urine osmolarity.

The papillary Na concentration also linearly increased as a function of the urine osmolarity until the Na concentration reached a level of 350 mEq/kg tissue water after which there has no further increase in Na. In other words, the renal concentrating operation seems to be carried out by two me chanisms: the first by increasing the concentrations of both Na and urea in the renal medulla until the former reaches a maximum, and the second by increasing the urea concentration only.

(8) The tissue concentration of K in the kidney was highest in the cortex and decreased progressively toward the papilla. Moreover, the tissue concentration of K at a given portion of the kidney was not different among 4 groups.

These results indicate that the amount of protein intake seems to determine the amount of salt intake while the amount of salt intake does not regulate the amount of protein intake. This finding consistent with the view speculated earlier by Kim

(1963) and may have an important bearing on the dietary habit of the people who are usually living on a low protein diet, However, the underlying mechanism for this interrelationship between the protein and the salt intake is yet to be studied. It is also clear from this investigation that the enhancement of renal concentrating operation in the high protein dietary group is attributable to the ability to concentrate urea in the renal

medulla. Although both Na and urea are the mast important determinants of the medullary osmotic gradient, the renal medulla can not concentrate Na beyond a certain level. On the other hand, urea can be concentrated in the renal medulla without showing any maxim71 level whereby providing additional amounts of solute to

the renal medulla for further water reabsorption in the collecting duct.