suffering from hyperthyroidism before and after treatment have shown variable J. Physiol. (1958) I42,

Transcription

1 447 J. Physiol. (1958) I42, BONE CALCIUM AND SODIUM CONTENT AND THE EXCHANGE OF RADIOSODIUM IN BONES FROM RATS TREATED WITH THYROXINE AND PARATHORMONE BY D. S. MUNRO, R. S. SATOSKAR AND G. M. WILSON From the Department of Pharmacology and Therapeutics, University of Sheffield (Received 4 February 1958) In healthy rats the proportion of sodium relative to calcium in bone is constant (Munro, Satoskar & Wilson, 1957). Nevertheless, after removal of sodium from the body by intraperitoneal dialysis or following adrenalectomy, the amount of sodium in bone falls although there is no change in the calcium content (Munro, Satoskar & Wilson, 1957, 1958). However, little is known about the influence of calcium loss on bone sodium metabolism. Skeletal decalcification can be produced by parathormone, which increases the urinary excretion of calcium (Albright, Bauer, Ropes & Aub, 1929; Woods & Armstrong, 1956). This method has been used in the present work to determine whether there is any associated change in bone sodium. Decalcification of the skeleton has been reported in cases of thyrotoxicosis (Albright et al. 1929; Aub, Bauer, Heath & Ropes, 1929; Logan, Christensen & Kirklin, 1942; Puppel, Gross, McCormick & Herdle, 1945; Krane, Brownell, Stanbury & Corrigan, 1956). Measurements of exchangeable sodium in patients suffering from hyperthyroidism before and after treatment have shown variable results difficult to interpret (Munro, Renschler & Wilson, 1958). The suggestion was made that some of the results might be due to alterations in the composition of bones produced by the disease, although there is no direct information with regard to sodium. Accordingly, in the present series of experiments, the action of thyroxine and parathormone on the calcium content of bone has been studied in rats, and measurements have also been made of sodium content of bone and exchange with radiosodium. METHODS Male albino rats were used and were weighed regularly throughout the experimental period. The methods of measuring the water, sodium, calcium and the radioactivity in the bones have been described previously (Munro et al. 1957). Serum concentrations of sodium and calcium were

2 448 D. S. MUNRO, R. S. SATOSKAR AND G. M. WILSON measured by flame photometry. Parathormone was given by intramuscular injection in a dose of 1 U.S.P. units daily. L-Thyroxine sodium was given in drinking water in a concentration of 5,ugIlOO ml., or by intramuscular injection in a dose of up to 55,ug/day. RESULTS Effect of thyroxine on bone composition. Thyroxine was given in increasing doses to six rats over a period of 9 weeks. For the first 5 weeks L-thyroxine sodium was added to the drinking water in a concentration of 5 /g/1 ml. This was then supplemented by intramuscular injections of 55,ug of L-thyroxine sodium on alternate days for 2 weeks, and finally daily for the last 2 weeks. At the same time another six rats, initially of similar weight, received corresponding injections of water. Definite evidence of hyperthyroidism appeared in the treated rats. Their mean weight was 83% of that of the control rats by the end of the treatment. The rats receiving thyroxine kept discretely apart in their cage while the control animals commonly huddled closely together in one corner. At death the hearts of the treated rats were noticeably larger and were approximately 5 % greater in weight. However, this degree of hyperthyroidism did not produce any definite changes in bone composition (Table 1). Effect of parathormone on bone composition and the release of 22Na. The first observations were carried out on twelve rats each given 1,c of 22Na shortly after weaning. After a further 1-12 weeks, intraperitoneal injections of NaCl solution.9 % (w/v) were given. This greatly increased the turnover of sodium in the extracellular fluid and ensured that any 22Na subsequently retained was exclusively in the bones. The rats were then divided into two groups of six and kept in two separate metabolism cages. After some preliminary measurements of whole-body radioactivity the rats in one group received five daily injections of 1 U.S.P. units of parathormone, while the others were given injections of distilled water. At the end of this period all the rats were given an intraperitoneal injection of 24Na and were killed 24 hr later. The results of the studies of bone composition are shown in Table 2. The administration of parathormone did not alter body weight. The total urinary excretion of calcium from the treated rats during the period of injections was 4-5 m-equiv, but only -65 m-equiv from the controls. There was also an increase in the urinary loss of sodium from the treated rats, which excreted 82 m-equiv in comparison with 55 m-equiv in the controls. The serum calcium level, measured on a pooled sample, was greater in the treated group but there was no difference in the serum sodium concentrations. The water and sodium contents of the bones in the two groups were not significantly different. The bone calcium was lower in the treated rats (P <.1). There was no change in the 24Na relative specific activity of bone sodium and the loss of 22Na from the bones was not increased by the parathormone injections. The

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4 45 D. S. MUNRO, R. S. SATOSKAR AND G. M. WILSON 22Na remaining in these animals was located in the bones and no 22Na radioactivity could be detected in the serum samples. A second series of observations with parathormone was then carried out on seven rats given 22Na after weaning. The design of the experiments was similar except that the rats were not killed until 5 weeks after the last of the six daily injections 'of parathormone. Measurements of the loss of 22Na with the whole body counter were continued up to the time of death. The weights of the rats were slightly greater than in the first series and those treated with parathormone were lighter at death. Throughout the longer period of study the rate of loss of 22Na from the body was similar in the two groups. There was a significant decrease in bone calcium in the rats receiving parathormone (P <.2) and a slight, insignificant decrease in bone sodium. Measurements of blood and bone radioactivity after death again established that the 22Na was confined to bone. DISCUSSION Some connexion between the thyroid gland and calcium metabolism has long been suspected (Thomson & Colip, 1932). A greatly increased excretion of calcium and rarefaction of bones have been noted in cases of long-standing thyrotoxicosis (Aub et al. 1929; Puppel et al. 1945), although skeletal decalcification demonstrable radiologically is rare in this disease (Williams & Morgan, 19. The administration of thyroid hormone to normal dogs produced an increase in calcium excretion without any changes in serum calcium levels (Logan et at. 1942). However, severe hyperthyroidism in adult rats, brought about by feeding desiccated thyroid, did not cause decalcification of bones, nor was there any evidence of lack of calcification in rapidly growing animals (Smith & McLean, 1938). Similarly, from comparison of the skeletons of twin sheep, one of which was thyroidectomized, Todd, Wharton & Todd (1938) found no modification of bone texture, weight or thickness. Bell & Cuthbertson (1942) observed in their experiments in rats that administration of thyroid gland (thyroideum siccum, B.P.) produced a greater reduction in soft tissue than in mineral matter, the quality of the bone being unaffected. Furthermore, in a chronic experiment, they did not observe any significant difference in the percentage of calcium in the femurs of control and thyroidtreated rats. Similarly, in the present experiments, there was reliable evidence that a severe degree of hyperthyroidism was produced in the rats, but no abnormalities in calcium or sodium metabolism were detected. It is known that the administration of parathyroid extract to rats increases the urinary excretion of calcium and decreases the bone calcium content (Thomson & Colip, 1932; Logan, 194; Talmage, Lotz & Comar, 1953; Bacon, Patrick & Hansard, 1956; Woods & Armstrong, 1956). However, the results in rats are somewhat variable and the rat can develop resistance to the action

5 THYROXINE, PARATHORMONE AND BONE SODIUM 451 of parathormone within a few days of injection (Thomson & Collip, 1932; Woods & Armstrong, 1956). Following injections of parathyroid extract rapid resorption of bone has been demonstrated, both organic bone matrix and its associated bone salts being resorbed simultaneously (McLean & Bloom, 1941). In the rats used in the present studies the bone calcium fell after parathormone administration but, though the urinary loss of both sodium and calcium rose, there was no alteration either of bone sodium content or of the exchange of bone sodium with 22Na or 24Na. Increased urinary sodium loss after parathormone has also been reported by Ellsworth & Nicholson (1935). The observations of Taylor & Moore (1956), on pullets depleted of calcium by their first period of egg production, showed that after severe losses of calcium the bone sodium content increased. The disturbance of calcium metabolism was far greater than in the present experiments on rats. It is evident that under the conditions of these experiments administration of neither parathormone nor thyroxine is followed by any striking change in bone sodium metabolism. SUMMARY 1. Thyroxine given to rats in sufficient dosage to produce hyperthyroidism caused no definite changes in bone calcium or sodium metabolism. 2. Parathormone produced a significant decrease in bone calcium content but there were no associated alterations in bone sodium content. The availability of bone sodium for exchange with sodium isotopes remained within the normal range after the loss of calcium from the bone. The work was done during tenure by R. S. S. of a research fellowship granted by Glaxo Laboratories (India) Priv. Ltd. We are grateful for grants for the purchase of isotopes and apparatus from the Tuberculosis Research Fund of the University of Sheffield, the Endowment Fund of the United Sheffield Hospitals, and Glaxo Laboratories Ltd. REFERENCES ALBRIGHT, F., BAUER, W., ROPES, M. & AuB, J. C. (1929). Studies of calcium and phosphorus metabolism. IV. The effect of the parathyroid hormone. J. clin. Invest. 7, AUB, J. C., BAUER, W., HEATH, C. & ROPES, M. (1929). Studies of calcium and phosphorus metabolism. III. The effects of thyroid hormone and thyroid disease. J. clin. Invest. 7, BACON, J. A., PATRICK, H. & HANSARD, S. L. (1956). Some effects of parathyroid extract and cortisone on metabolism of strontium and calcium. Proc. Soc. exp. Biol., N. Y., 93, BELL, G. H. & CUTHBERTSON, D. P. (1942). The effect of various hormones on the chemical and physical properties of bone. J. Endocrin. 3, ELLSWORTH, R. & NICHOLSON, W. M. (1935). Further observations upon the changes in the electrolytes of the urine following the injection of parathyroid extract. J. clin. Invest. 14, KRANE, S. M., BROWNELL, G. L., STANBURY, J. B. & CORRIGAN, H. (1956). The effect of thyroid disease on calcium metabolism in man. J. clin. Invest. 35, LOGAN, M. A. (19. Recent advances in the chemistry of calcification. Physiol. Rev. 2, LOGAN, M. A., CHRISTENSEN, W. R. & KHRuLIN, J. W. (1942). Thyroid and parathyroid hormone effects on calcium and phosphorus metabolism. Amer. J. Physiol. 135,

6 452 D. S. MUNRO, R. S. SATOSKAR AND G. M. WILSON MCLEAN, F. C. & BLOOM, W. (1941). lcification and ossification-mobilization of bone salt by parathyroid extract. Arch. Path. 32, MuwRo, D. S., RENSCHLER, H. & WILSON, G. M. (1958). Exchangeable potassium and sodium in hyperthyroidism and hypothyroidism. Metabolism, 7, MUNRO, D. S., SATOSKAR, R. S. & WILSON, G. M. (1957). The exchange of bone sodium with isotopes in rats. J. Physiol. 139, MuNRO, D. S., SATOSKAR, R. S. & WILSON, G. M. (1958). The effect of adrenalectomy on bone sodium metabolism. J. Physiol. 142, PUPPEL, I. D., GROSS, H. T., MCCORMICK, E. K. & HERDLE, E. (1945). The rationale of calcium, phosphorus and vitamin D therapy in clinical hyperthyroidism. Surg. Gynec. Obstet. 81, SMITH, E. E. & MCLEAN, F. C. (1938). Effect of hyperthyroidism upon growth and chemical composition of bone. Endocrinology, 23, TALMAGE, R. V., LOTZ, W. E. & COMAR, C. L. (1953). Action of parathyroid extract on bone phosphorus and calcium in the rat. Proc. Soc. exp. Biol., N. Y., 84, TAYLOR, T. G. & MOORE, J. H. (1956). The effect of calcium depletion on the chemical composition of bone minerals in laying hens. Brit. J. Nutr. 1, THOMSON, D. L. & COLLiP, J. B. (1932). The parathyroid glands. Physiol. Rev. 12, TODD, T. W., WHARTON, R. E. & TODD, A. W. (1938). The effect of thyroid deficiency upon bodily growth and skeletal maturation in the sheep. Amer. J. Anat. 63, WILLIAMS, R. H. & MORGAN, H. J. (19. Thyrotoxic osteoporosis. Int. Clin. 2, WOODS, K. R. & ARMSTRONG, W. D. (1956). Action of parathyroid extract on stable bone mineral using radiocalcium as tracer. Proc. Soc. exp. Biol., N. Y., 91,