ALDOSTERONE AND WATER AND SODIUM DIS- TRIBUTION IN NORMAL AND ADRENALECTOMIZED RATS

Transcription

1 ALDSTERNE AND WATER AND SDIUM DIS- TRIBUTIN IN NRMAL AND ADRENALECTMIZED RATS P. J. LENARD Department of Medicine, University of Sheffield, Royal Hospital, Sheffield, England (Revised manuscript received 28 January 1963) SUMMARY Adrenalectomy in the rat caused an increase of intracellular sodium, both total and relative ncentration in heart tissue and a decrease of both in abdominal muscle. These changes were reversed after administration of aldosterone. When aldosterone was given in similar doses to normal animals no changes were observed. It was ncluded that an increase in the intracellular sodium ncentration of heart and/or other soft tissues, including the adrenals, may stimulate the secretion of aldosterone. A possible regulating system is discussed. It is suggested that total sodium and its intracellular ncentration in muscle are influenced by the availability of aldosterone and sodium. INTRDUCTIN In a previous study (Leonard, 1962) it was shown that dietary sodium restriction or aminonucleoside nephrosis in rats was acmpanied by increases of total intra cellular sodium and of the ncentration of intracellular sodium in the heart, liver and adrenals as well as by an increased production of aldosterone. In nephrosis the intracellular sodium in the abdominal muscle was also increased. In an attempt to relate these changes to aldosterone production the effects on fluid mponents and electrolyte distribution in the tissues of rats were studied in the following experimental situations: (a) adrenalectomy, (b) aldosterone administra tion in normal rats, and (c) aldosterone administration in adrenalectomized rats. METHDS The methods were as described previously (Leonard, 1962). Twenty-two adrenal ectomized male albino rats weighing approximately 200 g. were used, ten shamoperated animals serving as ntrols. The adrenalectomized rats were divided into two groups, one receiving only 0-9 % saline to drink and the other only distilled water. All studies were carried out on the 6th day after adrenalectomy or sham operation. Aldosterone administration. The method used by Kelly (1960) was adopted. 1-0 µg. of aldosterone in 0-2 ml. of methanol was injected s.c. into the test animals and * Part of a thesis presented to the University of Sheffield for the Degree of Doctor of Philosophy. t Present address: Department of Medicine, Makerere University College, Kampala, Uganda, East Africa.

2 - 526 P. J. Leonard 0-2 ml. of methanol into the ntrols. Blood and tissue samples were llected 5 hr. later. The adrenalectomized animals received only distilled water to drink. Table 1 RESULTS shows the mean plasma electrolyte values and Table 3 the mean values for the tissue mponents and sodium distribution. The significant changes observed are set out in Table 2. It is assumed, in agreement with the findings of Conway & Hingerty (1946), that the amount of water/1, of plasma did not alter signifi cantly from one group to another. Adrenalectomy caused an increase of total po tassium, water and intracellular fluid in heart tissue. These changes were averted by the provision of saline to drink. The total intracellular sodium and intracellular Table 1. The effect of aldosterone administration on plasma electrolytes (m-equiv. I.) in normal and adrenalectomized (Adrex.) rats Table 2. Animals Adrex. water Adrex. saline Adrex. aid. Adrex. water Adrex. saline Adrex. aid. Animals Sham-operated Adrex. water Adrex. saline Adrex. aldosterone Intact Intact aldosterone (Means ± s.e.) No. of estimates Sodium ± ± ± ± ± Chloride 102-0±l ± ± ± ± Significant changes in adrenalectomized (Adrex.) animals mpared with sham-operated animals Tissue Heart Heart Heart Muscle Muscle Muscle Na* K* * m-equiv./100 g. fat free dry tissue. t g./100 g. fat free dry tissue. J m-equiv./kg. intracellular fluid. or Totalf water Intracell.f fluid : < or-: < : < Nac* [Na]ct sodium ncentration of heart tissue were increased in both groups of adrenalectom ized animals, but returned to the values found in the sham-operated animals after aldosterone administration. In abdominal muscle adrenalectomy caused a fall of total tissue sodium unless the supplement of saline was given. Total tissue potassium was increased while total intracellular sodium and intracellular sodium ncentration were decreased in both groups of animals. The effect of aldosterone administration was to restore the total intracellular sodium and intracellular sodium ncentration to ntrol levels. When administered in similar dosage to normal animals aldosterone caused no significant changes.

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4 528 P. J. Leonard DISCUSSIN The present study was carried out with the object of determining whether the increase in intracellular sodium ncentration of heart, liver and adrenals reported previously (Leonard, 1962) in sodium-restricted and aminonucleoside-treated rats was the cause or the nsequence of the increased production of aldosterone. Adrenalectomy caused an increase of total intracellular sodium and intracellular sodium ncentration in heart tissue and a decrease in abdominal muscle. These changes were reversed after administration of aldosterone. The saline supplement prevented any increase of total potassium, water and intracellular fluid in heart tissue as well as a fall of total tissue sodium in muscle, but did not alter the change in intracellular sodium in either tissue. Aldosterone at a dose level that produced changes in the tissues of the adrenalectomized rat had no effect in the normal animal. The increase of intracellular sodium ncentration of heart tissue after adrenal ectomy is similar to that found during sodium restriction or nephrosis (Leonard, 1962). From this it may be inferred that the increase of intracellular sodium in heart tissue is not a nsequence of increased aldosterone production since the change would hardly be observed in adrenalectomized animals if it were incidental with, or a result of, elevated aldosterone secretion. The lowering of the intracellular sodium ncentration of heart by administration of aldosterone to adrenalectomized animals also suggests that the increase observed after sodium restriction in normal animals would have preceded the increased production of the hormone. It may be that an increase in the intracellular sodium ncentration can stimulate aldosterone produc the stimulus tion. If the increase took place in a tissue other than the adrenal gland would have to be transmitted to the gland. If, however, there was an increase of intracellular sodium ncentration in the adrenal itself no transmitting system would be required. Such a change was seen in sodium restriction and experimental nephrosis (Leonard, 1962). There is no direct evidence to show that this preceded the increased production of aldosterone, but as the was change similar to that seen in heart in both of these nditions it seems likely that it did in fact precede the increased secretion of the hormone. Thus an increase in the intracellular sodium ncentration of heart and/or other soft tissues including the adrenals may lead to an increase in the secretion of aldosterone. A possible regulating system would be an increase of intracellular sodium ncentration leading to an increase in aldosterone secretion. The aldosterone would act on the kidney to retain sodium, at the same time reversing the increase in intracellular sodium and thus shutting the mechanism off. How the increase in intracellular sodium would be effected is not clear, but anything which caused an increase would stimulate production of aldosterone. It would appear that changes in total sodium and its intracellular ncentration in muscle are related to the availability of aldosterone and sodium. Thus in mplete absence of aldosterone (following adrenalectomy) both were reduced; with an in creased production of aldosterone and a low sodium intake (dietary restriction of sodium) no change was observed, and in the presence of an adequate intake of sodium and an increased production of the hormone (in nephrosis) both were in creased (Leonard, 1962). The formation of oedema in experimental nephrosis results from the increased aldosterone level. Das Gupta, Kalant & Giroud (1959) showed

5 Aldosterone and sodium distribution 529 that adrenalectomized nephrotic rats did not beme oedematous until aldosterone was administered at a dose approximating the levels secreted by the adrenals of the of aldosterone with or without oedema nephrotic animal. Thus an increased production formation uld be explained by a mmon increase of intracellular sodium n centration of soft tissue stimulating the increased production while changes in the distribution of sodium and water in muscle depend on the subsequent availability of aldosterone and sodium. In ngestive cardiac failure with oedema normal secretion and excretion as well as hypersécrétion and hyperexcretion of aldosterone have been reported in human subjects and dogs (Ulick, Laragh & Lieberman, 1958; Muller, Riondel, Manning & Mach, 1956; Cox, Singer & Verel, 1959; Davis, Pechet, Ball & Goodkind, 1957; Luetscher & Johnson, 1954). Little information is available on the distribution of sodium in the tissues in cardiac failure. Flear, Crampton & Matthews (1961) noticed an increase in total sodium and chloride of muscle in patients with severe ngestive cardiac failure (P < 0-001) and to a lesser degree in those with mild or moderate failure (P < 0-05). The increase in total sodium was acunted for by the increase in extracellular fluid in those with mild or moderate failure, while in those with severe failure the increase was largely due to an increase in the amount and ncentration of intracellular sodium. The changes in the group with severe cardiac failure are identical with those observed in muscle in experimental nephrosis (Leonard, 1962). Unfortunately aldosterone measurements were not carried out in the study of Flear et al. (1961), so it was not possible to relate the levels in the different groups. The differences between observed levels of aldosterone in ngestive heart failure may be due to differences in the severity of the ndition from one study to another. The intracellular sodium ncentration in muscle is known to increase with the were observed in the severity of the disease (Flear et al. 1961), and if similar changes soft tissues it would explain why in some studies an increased secretion or excretion of aldosterone has been found while in others normal levels were reported. The failure of aldosterone to produce changes in the normal rat at a dose level which was effective following adrenalectomy is similar to the observation that DCA (at a dose level adequate to maintain adrenalectomized rats) has little effect on normal animals. The author wishes to thank Prof. C. H. Stuart-Harris and Dr. Singer for their enuragement in this project and Mrs M. Pearse for assistance with the animal work. Thanks are also due to CIBA Laboratories Ltd., Horsham, Sussex, for generous gifts of aldosterone. This investigation was supported by a grant from the Medical Research Council, London.

6 530 P. J. Leonard REFERENCES Conway, E. J. & Hingerty, D. J. (1946). The influence of adrenalectomy on muscle nstituents. Biochem. J. 40, 561. Cox, J. R., Singer, B. & Verel, D. (1959). The relationship between urinary aldosterone, plasma volume, extracellular fluid volume and total body water. Clin. Sci. 18, 569. Das Gupta, D., Kalant,. & Giroud, C. P. (1959). Experimental aminonucleoside nephrosis. (ii) Effect of adrenalectomy on fluid retention of aminonucleoside nephrosis. Proc. Soc. exp. Biol., N.Y., 100, 602. Davis, J.., Pechet, M. M., Ball, W. C. Jr. & Goodkind, M. J. (1957). Increased aldosterone secretion in dogs with right sided ngestive failure and in dogs with thoracic inferior vena cava nstriction. J. clin. Invest. 36, 689. Flear, C. T. G., Crampton, R. F. & Matthews, D. M. (1961). bservations on the electrolyte and water mposition of skeletal muscle in patients in ngestive cardiac failure, using an in vitro method for determination of inulin space. Clin. Sci. 21, 381. Kelly, R. H. (1960). Altered physiological status and Na and in intracellular particulates of rat kidney. Arner. J. Physiol. 198, 104. Leonard, P. J. (1962). Effect of sodium restriction and experimental nephrosis on tissue spaces and tissue sodium distribution in the rat. J. Endocrin. 25, 323. Luetscher, J. A. Jr., & Johnson,. B. (1954). bservations on the sodium retaining rtiid (aldo sterone) in the urine of children and adults in relation to sodium balance and edema. J. clin. Invest. 33, Étude de l'aldosteronurie chez le Müller,. F., Riondel, A. M., Manning, E. L. & Mach, R. S. (1956). sujet normal et chez le cardiaque oedémateux, (i) Effets des variations de l'apport en chlorure de sodium. Schweiz, med. Wschr. 86, Ulick, S., Laragh, J. H. & Lieberman, S. (1958). The isolation of a urinary metabolite of aldosterone and its use to measure the rate of secretion of aldosterone by the adrenal rtex in man. Trans. Assoc. Arner. Physic. 71, 225.