BRIT. J. SURG., 1967, Vol. 54, No. 3, MARCH

THE EFFECT OF ANTI-THYROID DRUGS ON THYROCALCITONIN SECRETION*

BY T. DUNCAN SENIOR REGISTRAR I N SURGERY, ROYAL INFIRMARY, ABERDEEN

AND A. D. CARE PRINCIPAL SCIENTIFIC OFFICER, ROWETT RESEARCH INSTITUTE, ABERDEEN

THYROCALCITONIN is the calcium-lowering hormone from the thyroid gland first observed by Hirsch, Gauthier, and Munson (1963). It has been extracted from the thyroid of a wide variety of species (Hirsch, Voelkel, and Munson, 1964) and has been demon- strated in human thyroid (Aliapoulios and Munson, 1965 ; Milhaud, Mouhktar, Bourichon, and Perault,

Thyrocalcitonin is secreted in response to hyper- calcaemic perfusion of the thyroid gland (Foster, Baghdiantz, Kumar, Slack, Soliman, and MacIntyre, 1964; Care, 1965).

Recently, Aliapoulios, Voelkel, and Munson (1966) have noted that, although normal human thyroid tissue, obtained during neck surgery for conditions other than thyroid disease, was a good source of thyrocalcitonin, extracts made from hyperplastic human thyroid surgically resected in the treatment of hyperthyroidism were inactive when tested for thyrocalcitonin activity. Milhaud and others (1965), on the other hand, found activity in both normal and hyperplastic glands.

Since patients with hyperthyroidism normally receive antithyroid drug therapy prior to surgery when hyperplastic thyroid tissue is obtainable for assay of thyrocalcitonin activity, an experimental study was undertaken to determine the effect of the administration of antithyroid drugs on thyrocalci- tonin secretion.

1965).

MATERIALS AND METHODS The pig was chosen as the experimental animal

because in this species the thyroid is well separated anatomically from the parathyroids and because pig thyroid is known to be a good source of thyrocalci- tonin. The Large White pigs used were aged about 3 months and weighed about 20 kg. Methylthiouracil was chosen as the antithyroid drug to be given since it had been found to be one which readily rendered the thyroid hyperplastic in the pig. The treated animals received 600 mg. of methylthiouracil daily for 5-9 weeks prior to the experiments. Carbimazole, in a dose of 45 mg. daily for 3-4 weeks, was also used, but the results, although similar to those obtained with methylthiouracil, were less conclusive.

The altered secretion of thyrocalcitonin by the thyroid as a result of antithyroid drug treatment was studied in two ways.

First, with the animals under halothane anaes- thesia, the thyroid gland was perfused in situ with hypercalcaemic blood for 1-2 hours. The resultant

* This article is based on a communication given to the Surgical Research Society.

fall in systemic plasma calcium concentration was taken as an indication of increased thyrocalcitonin secretion (Care, Duncan, and Webster, 1966, 1967). The effects of such perfusion in 5 methylthiouracil- treated animals were compared with those in 5 untreated animals as controls.

Secondly, the control of hypercalcaemia, pro- duced by an intravenous calcium infusion, before and after thyroidectomy, was studied. Under anaes- thesia animals were infused intravenously for I hour with 10 per cent calcium gluconate at a rate of 14 mg. per kg. body-weight per hour. The effect of this infusion on the systemic plasma calcium concentra- tion in the intact animal was compared with the effect in the same animal 24 hours after thyroidec- tomy. The results in 2 untreated and 2 methyl- thiouracil-treated animals were then compared.

Analytical Procedures.-Plasma was separated within 15 minutes of sampling and the calcium concentration determined immediately afterwards by titration against EDTA with murexide indicator, using a photoelectric titrator (Evans Electro Selenium Ltd.) to detect the end-point. The values were corrected for changes in the plasma proteins.

RESULTS During hypercalcaemic perfusion of the thyroid

the average maximum percentage fall in the systemic plasma calcium concentration in the control animals was 23 f3 . In the methylthiouracil-treated animals, whose thyroids were on average five times heavier than normal and histologically hyperplastic, the maximum percentage fall was only 7 f I (Fig. I).

Because the plasma protein-bound iodine con- centration in these goitrous pigs was approximately half the normal value, it might be argued that the above lack of response was associated with a low concentration of circulating metabolic thyroid hor- mones. However, I methylthiouracil-treated animal received metabolic thyroid hormones before and during the experiment (20 yg. of triiodothyronine and 300 yg. of thyroxine I.M. on the day before, and 20 pg. of triiodothyronine I.M. on the morning of the experiment) without showing any increased response to the hypercalcaemic stimulus.

That the smallness of the systemic hypocalcaemic response in the methylthiouracil-treated animals was due to failure of the thyroid to release thyro- calcitonin, rather than failure of the target organ to respond to the hormone, was suggested by the effect of an exogenous dose of 25mg. of porcine thyro- calcitonin extract given parenterally midway through one perfusion experiment. Following the initial small systemic hypocalcaemic response produced by

DUNCAN AND CARE : THYROCALCITONIN SECRETION I97

the hypercalcaemic perfusion, a further fall in the systemic calcium occurred after the administration of the exogenous thyrocalcitonin (Fig. 2). A normal hypocalcaemic response to exogenous porcine thyro- calcitonin was also obtained in two other experi- ments.

It has been shown that in normal pigs the control of hypercalcaemia produced by an intravenous

In the present study the thyroid gland, rendered hyperplastic as a result of methylthiouracil admini- stration, showed an impaired ability to secrete thyrocalcitonin. This may have been due to the hyperplasia per se and, if the hyperplasia of the thyroid in thyrotoxicosis has a similar effect on thyrocalcitonin secretion, the resulting deficiency of this hormone would provide an additional causal

t Thyroldectomy

Normal Ca High Ca 1 ~

2 4 6 Hours

FIG. 1.-The effect of hypercalcaemic (7.1 mEq. Ca per litre) perfusion of the thyroid on systemic plasma calcium concentration.

calcium infusion is impaired after thyroidectomy (Care and others, 1966, 1967). The systemic plasma calcium concentration rises higher and returns to normal more slowly after thyroidectomy. This is interpreted as an indication of the loss of the calcium- lowering effect of thyrocalcitonin with removal of the thyroid. In the methylthiouracil-treated animals, however, there was very little difference in the effect of the calcium infusion before and after thyroidec- tomy. Indeed, the infusion prior to thyroidectomy produced changes in the systemic plasma calcium very similar to those produced by the infusion in the untreated animals after thyroidectomy (Fig. 3). In other words, in the treated animals the calcium- lowering potential of the thyroid, i.e., its ability to secrete thyrocalcitonin, was considerably impaired.

DISCUSSION Even before the existence of thyrocalcitonin was

demonstrated, it was recognized that the thyroid played a role in calcium metabolism and that abnor- malities of calcium metabolism occurred in thyroid disease.

In thyrotoxicosis an increased rate of turnover of calcium in the skeleton has been demonstrated (Krane, Brownell, Stanbury, and Corrigan, 1956) and an increased loss of calcium in the faeces and urine has been noted (Aub, Bauer, Heath, and Ropes, 1929; Wayne, 1960). Rarely, hypercalcaemia has been described (Rose and Boles, 1953). The mechanism of this hypercalcaemia remains uncertain. Harrison, Harden, and Alexander (1964) and Harden, Harrison, Alexander, and Nordin (1964) have produced evidence indicating that in thyrotoxicosis there is a secondary, possibly compensatory, hypoparathyroid- ism and they suggest that failure of this parathyroid inhibition may be responsible for the hypercalcaemia occasionally seen in thyrotoxicosis.

25 mg thyrocalcironin

I

1 HIrh calcium I

U Hours '

FIG. 2.-The effect of exogenous porcine thyrocalcitonin on systemic plasma calcium concentration during hypercalcaemic (6.3 mEq. Ca per litre) perfusion of the thyroid in a methyl- thiouracil-treated pig. The thyrocalcitonin was extracted from porcine thyroid glands as far as the trichloracetic acid precipitate stage, according to the method of Tenenhouse, Arnaud, and Rasmussen (1965).

Methylthiouracil-treated pig Normal pig

fl Beiore thyroidectomy Before thyroidectomy 71

Em After thyroidectomy

I I 3 5 I 3 3

Hours Hours

FIG. 3.-The effect on systemic plasma calcium concentration of a I-hour I.V. infusion of calcium gluconate, before and after thyroidectomy, in normal and methylthiouracil-treated pigs of similar age and weight. The shaded areas represent the periods of infusion (14 mg. Ca per kg. body-weight per hour).

factor in the hypercalcaemia of this condition. However, since the hypercalcaemia of thyrotoxicosis is rapidly corrected by the administration of anti- thyroid drugs (Bortz, Eisenberg, Bowers, and Pont, 1961) it would seem probable that, if reduced thyro- calcitonin secretion does occur in thyrotoxicosis, it is not a major contributory factor in this hyper- calcaemia.

198 BRIT. J. SURG., 1967, Vol. 54, No. 3, MARCH

SUMMARY BORTZ, W., EISENBERG, E., BOWERS, C. Y.. and PONT. M. Experimental evidence is presented which indi-

cates that the thyroid gland, rendered hyperplastic as a result of the administration of methylthiouracil, has an impaired ability to secrete thyrocalcitonin.

I t is suggested that diminished thyrocalcitonin secretion is not a major contributory factor in the hypercalcaemia occasionally present in thyrotoxicosis.

Acknowledgements.-We wish to thank Pro- fessor s. C. Frazer and Mr. w. Michie for their advice during this study and we are grateful to Mr. D. Webster for providing the porcine thyrocalcitonin extract. One of us (T. D.) was supported by a M.R.C. research grant during the period of this work.

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-- VOELKEL, E. F., and MUNSON, P. L. (1966),

AUB, J. C., BAUER, W., HEATH, C., and ROPES, M. (I929),

Forum, 15, 55.

J . clin. Endocr., 26, 897.

J. clin. Invest., 7, 97.

(1961), Ann. intern.-Med., 54, 6;o. CARE, A. D. (1965)~ Nature, Lond., 205, 1289. -- DUNCAN, T., and WEBSTER, D. (1966), J, Endocr.,

34, 11.

FOSTER, G. V., BAGHDIANTZ, A., KUMAR, M. A., SLACK, E., SOLIMAN, H. A., and MACINTYRE, I. (1964), Nature, Lond., 202, 1303.

HARDEN, R. McG., HARRISON, M. T., ALEXANDER, W. D., and NORDIN, B. E. C. (1964),J. Endocr., 28, 281.

HARRISON, M. T., HARDEN, R. McG., and ALEXANDER, W. D. (1964),3. clin. Endocr. Metab., 24, 214.

HIRSCH, P. F., GAUTHIER, G. F., and MUNSON, P. L. (1963), Endocrinology, 73, 244.

-- VOELKEL, E. F., and MUNSON, P. L. (1964), Science, N .Y . , 146, 412.

KRANE, S. M., BROWNELL, G. L., STANBURY, J. B., and CORRIGAN, H. (1956), J . clin. Invest., 35, 874.

MILHAUD, G., MOUHKTAR, M. S., BOURICHON, J., and PERAULT, A. (1965)~ C. r. hebd. Sianc. Acad. Sci., Paris,

(1967), Ibid., in the press. - _ _ _ _ _

261,4513.

37, 1715. ROSE, E., and BOLES, R.'S. (1953), Med. Clins N . Am.,

TENENHOUSE, A., ARNAUD, C., and RASMUSSEN, H. (1965) , Proc. natn. Acad. Sci.. U.S.A.. 53, 818.

WAYNE, E. J. (1960), Br.-med. J . , - l , 78.

INTRAVENOUS FAT THERAPY-I NITROGEN BALANCE STUDIES

BY D. J. REID* SENIOR SURGICAL REGISTRAR, ST. THOMAS'S HOSPITAL, LONDON

FOR the majority of routine surgical procedures, the nutrition of the patient before and after surgery is not a problem. The period of relative starvation is well tolerated. There are, however, some cases where adequate attention to this aspect of treatment may be crucial to the survival of the patient.

I t is possible to exist in a state of relative mal- nutrition without any very obvious outward signs of deficiency. There is a broad zone between optimal nutrition and classical deficiency states in which exist a large number of cases of borderline unsatis- factory nutrition. It is not until the needs of the body suddenly increase during surgery that this chronic state of near deficiency may become an important factor in survival. During all the stages of surgical treatment there is an increase in demand for calories which is often far greater than is realized. Three or four times the calories required for a normal patient at rest may be required for the same patient in the early postoperative phase. Fever increases the metabolic rate. Destruction of body tissues has to be made good by protein synthesis, which requires energy. Wound healing requires protein and energy. At these times oral intake of food is often impossible, especially in operations on the gastro-intestinal tract. The deficiency is there- fore most acute as demand increases and supplies are withheld.

* Present address : Department of Surgical Research, Mayo Clinic, Rochester, Minnesota, U.S.A.

Intravenous fat in the form of intralipid (manu- factured by the Vitrium Company of Sweden and distributed by Messrs. Paine and Byme, Greenford, Middlesex) 20 per cent w./v. provides 2000 calories per litre. To provide the same number of calories in the form of 5 per cent dextrose solution would require 10 litres of intravenous fluid. Fat emulsions are therefore a very valuable means of providing high calorie intakes in small fluid volumes. The reason why they have not been used to a great extent in the past has been the problem of maintaining the fat particles in a line dispersion which was also stable on storage. Emulsifying agents are often toxic and their efficiency as an emulsifying agent often runs parallel with their toxicity. Intralipid is a soyabean oil emulsion, with egg-yolk phosphatide as an emulsifying agent and containing glycerol to maintain isotonicity. I t is proving to be relatively well toler- ated in comparison to former varieties of emulsion, such as lipomul. Fatalities were reported with the use of this emulsion and the side-effects were far too frequent and severe to warrant its use as a form of supportive therapy (Leveen, Hiduckenko, and Giordano, 1960; Leveen and Giordano, 1961). The reaction rate of intralipid is low. No fatalities have occurred following its use. Mild pyrexial reactions occur in approximately 2 per cent of all infusions, but these have never proved severe enough to contra-indicate the general use of this emulsion.

Definite proof of utilization of intravenous fat emulsions has come from radioactive isotope studies