METABOLISM OF INTRAVENOUSLY ADMINISTERED CHOLECALCIFEROL IN MAN

Following intravenous injection of (3H) cholecalciferol into healthy subjects the disappearance of label from the plasma was followed by the reappearance ("rebound") of (3H) radioactivity associated exclusively with cholecalciferol. Lipoprotein fractionation of plasma revealed an increasing association of label with protein rather than lipoprotein during the rebound phase. We conclude that the rebound of plasma radioactivity reflects the transfer of label from lipoprotein to Vitamin D-binding globulin in the liver followed by its release into plasma.     

SERUM THYROGLOBULIN IN THE DIAGNOSIS AND MANAGEMENT OF THYROID CARCINOMA

Serum thyroglobulin (Tg) was measured by radioimmunoassay in sixty-two control subjects, 163 euthyroid patients with nodular goitre and eighty-one patients with previously treated differentiated thyroid carcinoma. Tg was elevated in 65% of nodular goitres and failed to fall with thyroxine treatment in ten/fifteen patients treated. A diagnosis of differentiated carcinoma was confirmed in fourteen/sixty-four of these patients and Tg was elevated in twelve. Of sixty-five treated thyroid carcinoma patients without evidence of residual tumour, serum Tg was undetectable in thirty-nine, normal in twenty-four and elevated in two. There was evidence of residual tissue in the thyroid in seventeen of the patients with detectable Tg. Of the sixteen patients with residual tumour or metastases Tg was elevated in fifteen. There was a positive correlation between goitre size and Tg levels in multinodular goitre, and thyroid carcinomas of large bulk were associated with higher Tg levels. Serum Tg was normal in medullary carcinoma and in two patients with thyroid metastases from extra-thyroidal malignancies. High Tg levels in patients with residual metastases from thyroid carcinoma following thyroid ablation indicates Tg production by tumour tissue. Measurement of serum Tg of limited value in the differential diagnosis of nodular thyroid disease. It is particularly useful following surgery and 131I therapy for differentiated thyroid carcinoma. In these patients it gives confirmation of thyroid albation and may provide evidence of residual tumour tissue when the other tests are negative.     

DECREASED SERUM THYROID HORMONE LEVELS AND INCREASED TSH RESPONSE TO TRH IN INFANTS WITH COELIAC DISEASE

Plasma levels of thyrotrophin before and after the intravenous administration of 200 microgram of thyrotrophin releasing hormone have been studied in eleven patients with active gluten-induced enteropathy and in a group of twenty-one normal prepubertal children. In nine out of eleven coeliac patients an exaggerated and/or sustained response of plasma thyrotrophin is observed. Basal plasma thyrotrophin level is not significantly different from the value observed in normal children. However, plasma levels recorded 20 and 60 min after injection of the releasing hormone are significantly higher than in control children (at 20 min: P less than 0.01; at 60 min: P less than 0.001). Serum levels of dialysed triiodothyronine and thyroxine and of triiodothyronine are significantly lower in coeliac patients than in normal infants (P less than 0.01). These data support the evidence of an endocrine dysfunction in coeliac disease. It is not clear whether it is due to malnutrition and/or to some direct action of circulating gluten-peptides on the hypothalamus.     

PROLACTIN AND TSH RESPONSES TO BOTH DOMPERIDONE AND TRH IN NORMAL AND HYPERPROLACTINAEMIC WOMEN AFTER DOPAMINE SYNTHESIS BLOCKADE

A study of the effect of alpha-methyl-1-tryosine (metyrosine) blockade (2 g/d for 2 d) of dopamine (DA) synthesis on the PRL and TSH response to domperidone (DOM) and TRH in normal women and subjects with pathological hyperprolactinaemia is reported. In the normal subjects, there was a marked increase in basal PRL (51.7 +/- 11.1 vs 5.7 +/- 1.0 ng/ml) and the PRL and TSH responses to DOM were abolished. The PRL response to TRH was also reduced. In the hyperprolactinaemic subjects, metyrosine had no effect on basal PRL nor on the virtually non-existent PRL response to DOM, whereas it abolished the exaggerated TSH response. The conclusion is drawn that the response of both PRL and TSH to DA receptor blockers is really dependent upon DA inhibitory tone. A fall in this tone can also be postulated as responsible for the hyporesponsiveness of PRL to DOM frequently observed in pathological hyperprolactinaemia. In addition, the fact that metyrosine also abolished the exaggerated TSH response to DOM shows that the latter is totally dependent on enhanced DA inhibition of the thyrotrophs. Lastly, the reduced PRL response to TRH after metyrosine indicates that DA partly determines the ability of the lactotrophs to respond to TRH.     

THE TSH, FSH AND PROLACTIN RESPONSES TO CONTINUOUS INFUSIONS OF TRH AND THE EFFECTS OF OESTROGEN ADMINISTRATION IN NORMAL MALES

Four normal males received a constant infusion of 0.9% NaCl for 1 hr followed immediately by 500 μg of TRH infused over the same period. A rise in serum TSH was observed in all subjects while in three there was also a significant FSH response. The prolactin response, unlike that of TSH, was markedly pulsatile indicating that different mechanisms exist for the release of these two hormones from the pituitary after TRH. Circulating levels of LH were unaffected. Ethinyl oestradiol, 30 μg daily for 3 days, was administered to two of the subjects and the infusions were repeated. Both basal FSH and LH levels were depressed, as was the FSH response to the infusion of TRH. By contrast, however, the TSH response to thyrotrophin releasing hormone was enhanced after oestrogen. In one subject the basal prolactin levels were significantly higher while in both there was an augmented prolactin response to TRH, the pulsatile pattern of release being maintained.     

A COMPARISON OF CALCIUM PENTAGASTRIN AND TRH TESTS IN SCREENING FOR MEDULLARY CARCINOMA OF THE THYROID IN MEN IIA

Intravenous injections of calcium gluconate and pentagastrin (CPG) or TRH were compared as secretagogues for calcitonin (CT) in screening for medullary thyroid carcinoma (MTC) in multiple endocrine neoplasia type IIA (MEN IIA). Administration of CPG resulted in a prompt increase in plasma CT in all five patients with MTC studied, one of whom had a normal baseline value (peak 412-371,000 ng/l, 636-4847% above basal). TRH produced a rise in plasma CT levels only in MTC patients with elevated basal values; the magnitude of increase was less than that observed with CPG (peak 168-17,200 ng/l, 113-180% above basal). CT levels did not rise above 300 ng/l with either test in four unaffected first-degree relatives of MEN IIA patients, three subjects with sporadic unilateral phaeochromocytomas and five controls with essential hypertension. CPG remains the CT secretagogue of choice in screening for MTC in MEN II A.     

SERUM THYROGLOBULIN CONCENTRATIONS AND 131I WHOLE BODY SCANS IN THE DIAGNOSIS OF METASTASES FROM DIFFERENTIATED THYROID CARCINOMA (AFTER THYROIDECTOMY)

SUMMARY. Measurements of circulating thyroglobulin (hTg) and ¹³¹I whole body scan were performed in 101 patients with differentiated thyroid carcinoma who had been subjected to surgical thyroidectomy and ¹³¹I ablation of remaining thyroid tissue. All 45 patients with positive scans (i.e. functioning metastases) had elevated hTg concentrations. Of fifty-six patients with negative scans forty-two had undetectable or very low hTg levels and were considered to be free of metastatic thyroid tissue, whereas fourteen showed the presence of non-functioning metastases in the clinical and/or radiological examination. In this group of patients, eleven had elevated serum hTg levels while the other three patients had detectable hTg concentrations within the normal range. These results indicate that serum hTg measurements correlate very well with scan findings and have the added advantage of detecting non-functioning metastases which would not be detected by scanning. We concluded that measurement of serum hTg may be used together with scanning, as the first step in the follow-up of thyroidectomized patients with differentiated thyroid carcinoma.     

EFFECT OF ORALLY ADMINISTERED CHELATING AGENTS EDTA,DTPA AND FRUCTOSE ON RADIOIRON ABSORPTION IN MAN

In order to assess the effect of orally administered chelating agents on iron absorption in man, experiments were carried out with ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and fructose. Sixty-eight radio-iron absorption tests were carried out on 17 hæmatologically normal adult volunteers. The dose in each test consisted of 5 mg. of elemental iron labelled with 2 µCi. of ⁵⁹Fe, 50 mg. of ascorbic acid and the chelating agent present in a 0 : 1, 1 : 1, 10 : 1 or 50 : 1 molar ratio with respect to iron. EDTA and DTPA had no significant effect on iron absorption when given in a 1 : 1 ratio, but reduced it when given in a ratio of 10 : 1 or 50 : 1. Fructose had no significant effect on iron absorption when given in a 1 : 1 or 10 : 1 ratio, but increased it when given in a 50 : 1 ratio. The effect of these chelating agents was not due to urinary excretion of chelated iron. These studies show the importance of the molar ratio of chelating agent: iron when the role of orally administered chelating agents on iron absorption is considered, and confirm that the absorption promoting effect of fructose applies to man as well as to the rat and rabbit. The enhancement of iron absorption by fructose could have clinical importance for a number of reasons: iron-fructose chelate should be an efficient hæmematinic in the treatment of iron deficiency anæmia; and it may play a role in the development of siderosis in the alcoholic who drinks wine containing fructose.     

SERUM TSH AND THYROID ANTIBODY STUDIES IN ADDISON''S DISEASE

Thirty-three patients with Addison's disease have been investigated with particular reference to thyroid function, thyroid antibody status and serum TSH measurements. Of twenty-seven patients with idopathic or probably idiopathic Addison's disease, fifteen had antibodies against adrenal tissue and thirteen had thyroid microsomal antibodies. No patient with tuberculous Addison's disease had evidence of thyroid disease or of either adrenal or thyroid antibodies. The response to injected TSH was usually impaired in patients who had antithyroid antibodies in their serum. This test was cumbersome but appeared to indicate the reserve capacity of the thyroid. Serum TSH levels were raised in ten of the thirteen patients who had thyroid antibodies, including six whose protein bound-iodine levels were below 4.0μ/100 ml. Three antibody negative subjects also had an elevated TSH level. The most sensitive indication of subclinical thyroid disease appeared to be a positive thyroid antibody test. Estimation of the serum TSH level appeared to correlate with more advanced disease and with the earliest evidence of failure of thyroid function. It is suggested that serum TSH measurements are clinically helpful in patients with positive thyroid antibody testes and in patients with low or low normal proteinbound iodine levels.     

SERIAL SERUM THYROGLOBULIN MEASUREMENTS IN THE MANAGEMENT OF DIFFERENTIATED THYROID CARCINOMA

Serum thyroglobulin (Tg) was measured on repeated occasions in 416 patients with differentiated thyroid cancer for up to 7 years after initial therapy. All patients had thyroidectomy and/or ablative 131I therapy and all measurements were done while patients were receiving T4 replacement. Tg was measured using a double-antibody radioimmunoassay. Overall correlation between serum Tg concentration and presence or absence of cancer was 95.9%. At the time of initial measurement 295 patients had serum Tg less than 5 micrograms/l, and in latest analysis only 1.7% of these patients showed evidence of disease. Initially there were 19 patients of a total of 121 with serum Tg greater than 5 micrograms/l in whom no cancer was apparent. In eight of these 19 subjects recurrent or metastatic disease has been diagnosed up to 3.5 years after the first measurement indicating that in these cases serum Tg values were 'predictive'. Serum Tg appears to be a sensitive and specific means of detecting residual, recurrent or metastatic thyroid cancer and in most situations can replace routine, expensive and inconvenient radioactive thyroid scans; these should be performed when serum Tg values are elevated or when there is clinical evidence suggesting recurrence.     

CHARACTERIZATION OF TSH ANTAGONIST ACTIVITY IN THE SERUM OF PATIENTS WITH THYROID DISEASE

The ability of sera from patients with thyroid disease to block TSH stimulation of cyclic AMP release from isolated porcine thyroid cells has been assessed and the blocking activity characterized. TSH receptor binding activity was also measured. No blocking or receptor binding activity was detectable in patients with primary myxoedema (n = 23), Hashimoto's disease (n = 11), multinodular goitre (n = 6), or rheumatoid arthritis (n = 10). However, analysis of sera from 23 patients (out of an initial screen of 110 patients) with treated Graves' disease which did not stimulate cyclic AMP production in the bioassay showed that two of these sera contained powerful blocking and receptor binding activity. Both these patients had been treated with 131I. Analysis of the two sera by gel filtration on Sephadex G-200 indicated that blocking and TSH receptor binding activity were associated only with the IgG fraction. Digestion of the IgG with pepsin followed by reduction showed that both (Fab)2 and Fab fragments contained high levels of blocking and binding activity. Antibody divalency was not necessary therefore for TSH antagonist activity. However, our studies suggest that autoantibodies of this type with TSH antagonist activity do not occur frequently in patients from the Cardiff region with primary myxoedema, Hashimoto's or treated Graves' disease.     

SOMATOSTATIN INHIBITS THE PENTAGASTRIN-INDUCED RELEASE OF SERUM CALCITONIN IN MEDULLARY CARCINOMA OF THE THYROID

The effect of somatostatin on the secretion of calcitonin was studied in four patients with medullary carcinoma of the thyroid (MCT). The basal serum calcitonin level was markedly elevated in all cases. A bolus injection (100 μg) of somatostatin followed by an intravenous infusion (5 μg/min) for 60 min suppressed the basal calcitonin level in three of the four patients by 24–42%, while it had no inhibitory effect in one case. In another experiment, the pentagastrin-stimulated (6 μg/kg s.c.) calcitonin release was partially blocked by a simultaneous i.v. injection of somatostatin (200 μg) in all four patients studied. These experiments add human calcitonin to the list of hormones whose release is inhibited by somatostatin.     

STUDIES OF SERUM LONG-ACTING THYROID STIMULATOR (LATS) IN RELATION TO EXOPHTHALMOS AFTER THERAPY FOR THYROTOXICOSIS

Observations have been made on a series of 30 thyrotoxic patients before and after therapy, with particular attention to exophthalmos (measured by the Hertel exophthalmometer) and serial determinations of serum levels of protein-bound iodine (PBI) and long-acting thyroid stimulator (LATS). In 14 cases in which there was an exacerbation of exophthalmos (mean maximal increase of 2·8 mm. Hg) there was a greater fall in serum PBI levels (7.3 µg. per 100 ml.) than in 16 cases in which there was no such exacerbation (3.5 µg. per 100 ml.), although initial serum levels of PBI were the same in the two groups. The serum LATS level was more likely to be initially elevated in the group showing exacerbation. and a further rise was observed more frequently in this group following therapy, whether with antithyroid drugs, surgery or radio-iodine. Suppression of serum levels of LATS with azathioprine or steroids did not significantly affect the exophthalmos which had already developed in two cases. These observations suggest that a determination of serum level of LATS could be carried out advantageously before therapy. If a high level is seen, then exacerbation of exophthalmos is more likely to occur. Immunosuppressive therapy may be indicated in addition to antithyroid drug therapy. surgery or the use of radio-iodine if exacerbation is to be prevented. Further studies are suggested to try to define more clearly the susceptible group of patients and to assess the value of immunosuppressive therapy in preventing exacerbations of exophthalmos.     

FREE THYROID HORMONE LEVELS AND TSH RESPONSE TO TRH IN PATIENTS WITH AUTONOMOUS THYROID ADENOMATA AND NORMAL T3 AND T4

Free thyroid hormone levels together with basal and TRH stimulated TSH levels, have been determined in 50 patients with autonomous thyroid adenomata, who had normal serum total T3 and T4 values. Similar measurements were made in 33 healthy subjects. FT3 and FT4 plasma levels were significantly higher (P less than 0.01 and P less than 0.05 respectively), and basal and TRH stimulated TSH were significantly lower (P less than 0.05 and P less than 0.001 respectively) in the patients than in the controls. The TSH response to TRH was decreased in spite of normal free thyroid hormones in 25 patients and in a further ten both the delta TSH after TRH and the free fractions were normal. Eighteen patients were studied over periods from 4 37 months by repeating thyroid hormone levels and TRH tests. In six of them a change of these parameters toward toxicity was observed. The data obtained in the longitudinal study indicate that the values of free thyroid hormones and the result of the TRH test obtained by a single determination may represent different steps in the evolution of autonomous thyroid adenomata rather than a distinct pathophysiological condition.     

HORMONAL AND CARDIOVASCULAR RESPONSES TO DDAVP IN MAN

Hormonal and cardiovascular responses to 1-desamino-8-D-arginine vasopressin (DDAVP) were investigated in six normal adult volunteers. After overnight fluid deprivation, an intravenous injection of either DDAVP (0.4 microgram/kg) or the same volume of normal saline was administered. One hour later an intravenous infusion of hypertonic saline was commenced and continued over two hours. Five minutes following the DDAVP injection, facial flushing, a fall in diastolic blood pressure by an average of 13% and a rise in pulse rate by an average of 18% were observed. There was a significant increase in plasma renin activity and plasma cortisol concentration, but no significant changes were observed in plasma concentrations of LH, FSH, TSH, prolactin or GH. Following osmotic stimulation by hypertonic saline plasma AVP rose to the same extent in both the DDAVP and control studies. DDAVP (0.4 microgram/kg) was also administered to five subjects with cranial diabetes insipidus. Again facial flushing, increased facial temperature, a fall in diastolic pressure and a rise in heart rate were all observed, suggesting that DDAVP exerts its cardiovascular actions by a mechanism other than antagonism of circulating endogenous AVP.     

THE EFFECT OF PARTIAL THYROIDECTOMY FOR GRAVES'' DISEASE ON SERUM LONG-ACTING THYROID STIMULATOR PROTECTOR (LATS-P)

The effect of partial thyroidectomy on serum LATS-P has been investigated in twenty-one consecutive patients. Before surgery, LATS-P was detectable in seventeen (81%) but 1 year after operation only five (24%) had activity. The activity did not fall immediately after surgery but declined progressively throughout the year. In no patient was an increase in activity demonstrated; nor did LATS-P appear in those patients who did not have activity before operation.     

METABOLIC AND HORMONAL RESPONSES TO EXOGENOUS HYPERTHERMIA IN MAN

To study whether hyperthermia reproduces hormonal and metabolic responses seen in stress states such as mild infections, six normal male subjects underwent (i) a 3-h hot bath and (ii) a 3-h thermoneutral control period. During the hot bath body temperature rose by 1.2 +/- 0.03 degrees C (mean +/- SEM) and significant peaks of circulating growth hormone (56 +/- 9 vs 7 +/- 4 mU/l), adrenaline (310 +/- 34 vs 152 +/- 39 pmol/l), glucagon (19.2 +/- 4.3 vs 11.8 +/- 2.3 pmol/l) and cortisol were recorded together with slight hyperinsulinaemia (6.5 +/- 1.3 vs 5.3 +/- 1.0 mU/l, P less than 0.05). Hyperthermia was also accompanied by significant increases in circulating levels of free fatty acids (0.93 +/- 0.1 vs 0.46 +/- 0.1 mmol/l), 3-hydroxybutyrate (196 +/- 67 vs 50 +/- 18 mumol/l), glycerol (102 +/- 10 vs 48 +/- 5 mumol/l) and lactate. Blood alanine decreased and blood glucose remained constant. When an intravenous glucose tolerance test was performed during the last hour of hyperthermia signs of impaired first phase and enhanced second phase insulin responses were recorded. Calculated values for glucose disappearance also deteriorated (1.34 +/- 0.19 vs 2.04 +/- 0.50 %/min, P less than 0.05). We conclude that hyperthermia mimics most major metabolic and hormonal changes observed during mild infection and could provide a model to study these conditions.     

THYROID HORMONE KINETICS: IMPROVED METHOD FOR QUANTITATIVE SEPARATION AND MEASUREMENT OF THE VARIOUS RADIOIODINATED SPECIES IN SERUM AFTER RADIOIODOTHYRONINE INJECTION

An accurate and reproducible method for measurement of radioactive species in blood after in vivo injection of labelled iodothyronines is described. By extraction with high-affinity antisera, radioactive reverse T3 and T3 are separated from serum quantitatively. Radioiodide is quantitatively separated from radio-thyronine species and serum proteins by Sephadex G50 filtration. The residual mixture of radio-T4 and iodoprotein is quantitatively resolved by ion-exchange adsorption. Minimal misclassification of radiospecies occurs, and can be corrected for. Mean recoveries of various radiospecies added to serum were: radioiodide 98.9%, radio-rT3 87.6%, radio-L-T3 94.5%, radio-T4 98.0% and radioiodoprotein 94.5%. The performance of the method is superior to that of chemical methods such as trichloracetic acid precipitation, ion-exchange or alkaline Sephadex extraction, and chromatographic separation.     

RESPONSES OF NEUROHYPOPHYSIAL PEPTIDES TO HYPERTONIC SALINE AND INSULIN-INDUCED HYPOGLYCAEMIA IN MAN

In order to investigate the possible role of oxytocin in osmoregulation and its response to stress, plasma immunoreactive oxytocin was measured during hypertonic saline infusion and insulin-induced hypoglycaemia in a group of normal subjects, four patients with idiopathic diabetes insipidus and one patient with DIDMOAD syndrome (the syndrome of diabetes insipidus, diabetes mellitus, optic atrophy and deafness). The results were compared with those of plasma immunoreactive vasopressin to the same stimuli. As expected, there was a rise in plasma vasopressin in the normal subjects to both tests: this was absent in the patients with diabetes insipidus. Plasma oxytocin did not rise during hypertonic saline infusion in either group of subjects. The response of oxytocin to insulin-induced hypoglycaemia (0.15 U/kg soluble insulin) in normal subjects was much more variable. One highly symptomatic volunteer showed a marked rise in oxytocin. Two subjects also showed a rise when retested with 0.19 U/kg soluble insulin. There was no response of oxytocin to a standard-dose insulin test in the patients with diabetes insipidus. The data suggest that, in man, oxytocin is not involved in osmoregulation but that it may be secreted in response to marked hypoglycaemia.     

THE INVOLVEMENT OF THE PENTOSE SHUNT IN THYROID METABOLISM AFTER STIMULATION WITH TSH OR WITH IMMUNOGLOBULINS FROM PATIENTS WITH THYROID DISEASE. 1. THE GENERATION OF NADPH IN RELATION TO STIMULATION OF THYROID GROWTH

It has been shown previously that both thyrotrophin (TSH), and also immunoglobulins (Ig) derived from patients with goitrous Graves’disease, stimulate DNA-synthesis in guinea-pig thyroid tissue maintained in vitro. Here we describe the use of the same in vitro system and methods of quantitative cytochemistry to test the effect of these substances on the generation of NADPH, which is another indicator of the potential for growth. As could be predicted by its trophic action, TSH stimulated the generation of NADPH by glucose 6-phosphate dehydrogenase. The Ig-fraction from normal subjects depressed this activity. The Ig-fraction from Graves’disease patients with goitres stimulated the generation of NADPH, whereas the Ig from patients with Graves’disease but with minimal enlargement of the thyroid gland behaved like normal Ig. A similar lack of stimulation was found with Ig from patients with Pendred's syndrome, other dyshormonogenetic goitres, and autonomous single adenomas. In all specimens tested, there was good correlation between the amount of DNA-synthesis, measured by Feulgen cytophotometry, and the activity of glucose 6-phosphate dehydrogenase activity that generated NADPH. These results support the concept that there is a distinct type of autoantibody that influences thyroid growth.