INFLUENCE OF A LARGE AMOUNT OF SODIUM CHLORIDE INGESTION ON THE BASAL METABOLISM AND ON RESISTANCE TO COLD AND FROST-BITE

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1 INFLUENCE OF A LARGE AMOUNT OF SODIUM CHLORIDE INGESTION ON THE BASAL METABOLISM AND ON RESISTANCE TO COLD AND FROST-BITE KOREHIRO OGATA, NORIHIRO NASU, KAZUTOSHI HARADA AND MASAHARU KAMOTA * Department of Physiology and Hygiene, The Research Institute for Diathetic Medicine, Kumamoto University It is well known (1, 2) that various unpleasant symptoms such as edema of the face and limbs, disorders of the digestive organs, headache, feeling of weakness and languidness, pain in the eye etc. will occur three to four days after starting to take about 30g. of sodium chloride every day in spring or autumn, when the amount of perspiration is small. But it is reported by Ogata (3) and by Matsumoto (4) that sodium chloride amounting to 40g. or more a day is habitually taken through the winter months by residents of North Manchuria and yet no disorders in body functions are observed, while, in summer, their daily ingestion of sodium chloride amounts to only 20-30g. A similar tendency can also be observed in the animal kingdom. In North Manchuria animals are so hungry for salt in winter that they stale on the snow-covered fields and eat the stained snow. This apparent discrepancy in the amount of sodium chloride intake may be understood only when we take it into consideration that there is a marked variation in the ability to metabolize salt and the time of the year might play an important part in this variation. These subjects are, we believe, not only of physiological interest but are worthy of study as they are closely related to our daily life. In the present work the balance between sodium chloride intake and discharge as well as its effects on some functions are observed. METHODS Experiments were performed on young male Japanese in Mukden and in Kumamoto. The winter is much more severe in the former than in the latter. The amount of sodium chloride intake was estimated from the weight of food and an analysis table of foodstuffs. The amount of salt discharged into urine in 24-hour periods beginning at nine in the morning was determined by Morh's chlorine analysis method. The oxygen consumption was determined by using either Douglas bags or Knipping's apparatus. The determination of the rectal and surface temperature was made by Received for publication February 29,

2 304 K. OGATA, N. NASU, K. HARADA AND M. KAMOTA thermocouple with copper and constantan wire taking the emf. by a potentiometer. RESULTS Effects on basal metabolism In Mukden, a region of severe cold, the determination of basal metabolism and close investigation into sodium chloride equilibrium were conducted during the January-March period on male adults under normal daily routine. Fig. 1 shows one of the typical cases. While taking about 20g. of sodium chloride every day, the basal metabolism of the subject, Cal. per sq. m. per hour, was found to be within the normal range. From that time on, the daily intake of sodium chloride was increased by adding 10g. to Fig. 1. ord.: ordinary salt formula, inc.: increased salt formula, abs.: abstinenee of salt, B. M.: basal metabolism, U: volume of urine for a day, Cl: concentration of chlorine in urine, In.: NaCl intake for a day, Dis.: NaCl discharge for a day. each meal, making approximately 50g. daily total which is not less than the amount taken by the inhabitants in North Manchuria. The quantity of urine passed in a day increases suddenly, together with a rise in its sodium chloride concentration. In the case shown in fig. 1, no other remarkable changes than the quantity of urine and the high chloride concentration were seen during the first six days of the increased salt formula. On the seventh day a rise in basal metabolism, a feeling of warmth, good appetite and energetic feeling of the body appeared. When the extra administration of the salt was discontinued, the basal metabolism returned to the initial level. A fact worthy of note is that the high basal metabolism attained by means of a large amount of sodium chloride administration varies from day to day. A plain example of this sort of metabolism by giving the great amount of the salt again, was reproduced from the fifteenth to the twenty-fifth of February. When the sodium chloride intake was discontinued completely a significant fall in basal metabolism, reaching as low as Cal/m2/hr., was observed on and after the third day of NaCl-free formula, to say nothing of such abstinence symptoms as spasms of the muscles, depression of spirits, etc. During the October-November period an experiment according to the same procedure was conducted in Kumamoto, where the weather is temperate. It is illustrated in fig. 2. The subject usually took about 30g. of sodium chloride

3 in his daily diet and the balance between intake and discharge was maintained well. The basal metabolism then stood at Cal/m2/hr., which was well considered to be in the neighbourhood of the upper limit of the normal range. The metabolism rose on the third SODIUM CHLORIDE INGESTION ON BASAL METABOLISM AND ON RESISTANCE TO COLD g. of extra salt were given with each meal, in other words there was an intake of some 50-60g. every day. On the sixth day the subject had a swollen face, congestion of the ocular conjunctivae, and complained of a general feeling of weakness. The basal metabolism began to decline. It is a matter for consideration that a good deal of the salt should have been stored in the body on about the sixth day when some displeasing symptoms Fig. 2. ord.: ordinary salt formula, inc.: increased salt formula, abs.: abstinence of salt, B. M.: basal metabolism, U: were revealed, because the increased discharge of the salt in volume of urine for a day, Cl: concentration of chlorine in urine, In.: NaCl intake urine which resulted from the increased intake was far behind the for a day, Dis.: NaCl discharge for a day. increase in intake. The suggestive relation between the retention of sodium chloride and the fall in basal metabolism led us to undertake experiment in which the subject taking the increased salt formula was daily given 0.1mg. of Lumin, a photosensitizing dye in the cyanin series, in expectation of its diuretic effect. The results came up to our expectations: an increase in sodium chloride discharge in urine was followed by a rise in the basal metabolism as well as by the disappearance of all the unpleasant symptoms such as general feeling of weakness. The above two experiments led us to imagine that the influence of the ingestion of a large amount of sodium chloride might be different according to the time of year when the experiments were made. In consequence the experiment was repeated all through the year in Kumamoto. The results during the observance of the increased salt formula are summarized in the table. Maximum discharge of sodium chloride in urine stands for the maximum amount of discharge per diem during each series of experiments. During the July-August period the total amount of salt retained in the body before the symptoms of excess manifest themselves is dropped, since it was sultry enough day after day to cause a considerable degree of perspiration, through which some of the salt must have been lost in quantities which were not negligible but which we did not measure. Even with an almost constant daily intake of sodium chloride

4 306 K. OGATA, N. NASU, K. HARADA AND M. KAMOTA Table amounting to about 60g., the salt is discharged in larger amounts in urine in summer than in winter, while in autumn and winter much more salt can be retained before the unpleasant symptoms appear and it takes many more days to come to manifest the accumulation symptoms. Effect on resistance to cold Two groups of subjects were exposed to cold; one consisted of normal subjects (B) and the other consisted of subjects of high metabolic rate resulting from the increased salt formula (A). As an example a pair of thinly clothed subjects, one of them taking 50g. of sodium chloride every day, was exposed on the third day of the increased salt formula to the open air at 9-10 Ž. below zero. The subjects showed no great difference in oxygen consumption and surface temperatures during exposure to the cold. By the way the basal metabolism in Subject A had not yet increased. On the twelfth day (fig. 3) it was only 5 Ž. below zero but the exposure was made up by turning on an electric fan. In Subject A a rise in the oxygen consumption and a drop in surface temperatures, especially those at the Fig. 3. H1: DT 38 Ž., WT 23 Ž., C: DT -5 Ž., H2: DT 33 C., WT 20 Ž., Subject A: increased salt formula, Subject B: ordinary diet, O2: Oxygen consumption in cc/m2/min., TR: rectal temperature, TL: skin temperature at the chest, TH: skin temperature at the back of the hand, TV: skin temperature at the forearm.

5 SODIUM CHLORIDE INGESTION ON BASAL METABOLISM AND ON RESISTANCE TO COLD 307 distal ends of extremities were less in degree than in Subject B and in the course of exposure Subject A complained less than did Subject B. Effect on resistance to frost-bite As an index for this function, temperature reaction of skin vessels to cold, which is chiefly ascribed to the function of arteriovenous anastomosis, was employed. The procedure was described by Yoshimura (5) that the human middle finger was dipped into ice water up to its root for thirty minutes and the skin temperature at the back of its tip was taken every minute. During the stage of high metabolic rate due to increased sodium chloride ingestion the periodic fluctuation in the surface temperature of the middle finger due to severe cold was very active. Fig. 4 belongs to the same kind of experiment carried on upon the ear-lobe of a rabbit. For three days before the experiment extra sodium chloride totaling 12g. added to the usual feeding-stuff was given to Rabbit A. This was exposed to severe cold at 15.5 Ž. below zero together with Rabbit B as a control. On Rabbit B, 27minutes after exposure the ear-lobe was frozen and when it was thawed out in a hot chamber, it was congested. On the following day it was swollen. These were all signs of frostbite of considerable degree. In contrast to B, Rabbit A was not affected by chilblains at all, and during exposure the skin temperature stood higher and the periodic fluctuations in the skin temperature due to temperature reaction of skin vessels to cold was more prominent in Rabbit A. Fig. 4. C. F.: Cooling power after Kamae, «1: the ear-lobes on both sides were frozen, ª2: the congestion was remarkable, Subject A: increased salt formula, Subject B: ordinary diet. DISCUSSION It has been generally recognized by many authors that a daily intake of as much as 30g. of sodium chloride for 2-4days is enough to cause accumulation symptoms. On the contrary the present work demonstrates that a daily intake of 60g. can cause a rise in basal metabolism as well as in resistance to cold and frost-bite. These reactions are quite favourable to the regulation of body temperature in a cold environment. This also may explain the fact that the inhabitants in North Manchuria have an increased appetite for highly salted food in winter. Nevertheless it is a matter for consideration that the ingestion of salt may

6 308 K. OGATA, N. NASU, K. HARADA AND M. KAMOTA bring about some favourable results on one occasion and very unpleasant symptoms on the other. It is beyond question that both excess and deficiency in sodium chloride intake cause unfavourable symptoms and consequently the a- mount of intake which conditions the regulation of body temperature to severe cold must be found somewhere in the range between these extremes. This is illustrated plainly, for example, in fig. 2. When sodium chloride as much as 61g. on an average is taken, the discharge into urine averages 49.5g. daily. The unpleasant symptoms do not manifest themselves till 61.0g. in total are retained in the body on the sixth day. The unfavourable symptoms due to excess retention of the salt are all to be removed when balance is regained as a result of an increased discharge in urine through the administration of a diuretic, and also the basal metabolism rises again. A glance at the amounts of sodium chloride might give the impression that in so far as the salt intake and discharge were well balanced, the more the salt was exchanged, the more activated would be the metabolic function in general. To reason on this assumption an exchange on a larger scale must be made in winter when the discharge is expected to be increased because of the established fact that the intake is larger in winter than in summer. The maximum discharge of sodium chloride in urine during the period of increased salt intake is much higher, against expectation, from March to August than in the October-February period, and this coincides with the report by Suzuki (6) that in frogs isotonic sodium chloride solution injected into the hypodermic lymphatic spaces is discharged more easily when the surrounding temperature stands higher. As it has come to such a pass, we come to introduce another assumption, namely that the increased functions of the body depend on the amount of sodium chloride held in the body and that the season rather than the ambient temperature causes a marked difference in the maximum amount of retention without any ill effects. Now the assumption is proved to be true, that is, during the late autumn and winter, many more days are required and a much greater quantity of the salt is estimated to be retained in the body before the accumulation symptoms come out. All these discussions lead us to the following conclusions. The increased resistance to cold and frost-bite which is required through the winter months is attained by an increased ability to hold more salt without any accumulation symptoms as well as an increased sodium chloride requirement accompanied by a diminished ability to discharge the salt in urine, while in summer both a drop in the requirement and an increase of discharge in urine prevent the retention of salt in the body. In the present paper only a glance at the amount of sodium chloride taken in and discharged is described and the mechanism of hyperfunctions due to an increased amount of the salt held in the body will be discussed later. SUMMARY In spite of the common knowledge among physicians that the daily intake of as much as 30g. of sodium chloride will bring about disorders of various functions of the body to a considerable degree, the actual fact that the inhabit-

7 ants in North Manchuria take 40 g. or more every day during the winter months without any disorders in the body functions leads us to further study of the effect and significance of sodium chloride ingestion. 1) Daily intake of sodium chloride amounting to g. by adding 10 g. to each meal causes a gradual rise in basal metabolism, good appetite, and energetic feeling of the body after several days. In this stage of high metabolic rate due to increased salt ingestion, both a rise in the oxygen consumption and a drop in the surface temperatures during exposure to cold are less in degree and the subject complains less than normal subjects. It is also proved that the temperature reaction of skin vessels to cold in the middle finger of a human subject as well as in the ear-lobe of a rabbit is intense enough to offer resistance to frost-bite. 2) When the increased salt formula is continued beyond this favourable stage, the displeasing symptoms known to all which are due to deposit of the excess salt manifest themselves before long. 3) Generally speaking, a rise in the body functions seems to be accompanied not with an increased amount of exchange but with the amount of sodium chloride held in the body, and there exists a marked seasonal difference in the ability of salt metabolism: the maximum amount which can be retained without any symptoms of excess is far greater during the period in late autumn and winter than during the rest of the year, and the body can take more salt during the winter months and can discharge more in urine in summer than during the rest of the year. 1. KUNO, Y. Ase. Nara: Yotokusha Publ. Co., 1946 (Japanese). 2. KLINKE, K. Der Mineralstoffwechsel; Physiologic und Pathologle. Leipzig u. Wien: Franz Deuticke, OGATA, K. Kanrei to Taion-Chosetsu. Tokyo: Nanjo Publ. Co., 1949 (Japanese). 4. MATSUMOTO, H. J. Orient. Med. Vol.39, 1943 (Japanese). ibid. Vol.40, 1944 (Japanese). 5. YOSHIMURA, H. Jap. J. Physiol. 1: , SUZUKI, Y. J. Physiol. Soc. Jap. 11: 86-91, 1949.