Simple solid-phase radioimmunoassays for total tri-iodothyronine and thyroxine in serum, and their clinical evaluation

Effects of Zeranol® implants and dietary supplement on growth rate, endocrine status and blood metabolite levels of growing lambs at pasture

In a 2 × 2 factorial experiment, the effect of implants of the growth promoter Zeranol, with and without supplementary food, on the growth rate, blood metabolite and hormone profiles of lambs finished at pasture was examined. For lambs fed no supplement, Zeranol implants increased growth rates from 166 to 185 g/day (s.e. of difference = 11·4) whereas for animals fed supplement the response to Zeranol was much greater, the growth rates being 167 and 234 g/day (s.e. of difference = 12·8). Supplement given to lambs not treated with Zeranol replaced a proportion of the herbage intake while, in lambs given supplement and treated with Zeranol, herbage intake was greatly increased (P< 0·001). Plasma glucose and urea concentrations were not affected by treatment but non-esterified fatty acids (NEFA) were depressed and albumin levels increased by Zeranol implants, while supplementary food caused reductions in plasma NEFA and urea concentrations. It is suggested that Zeranol treatment and supplementary food acted synergistically through changes in insulin and growth hormone concentrations to induce a much larger increase in growth rate in the treated animals given supplementary food than in those given either Zeranol or supplement alone. The response to Zeranol may also have been altered by differences in thyroid hormone status associated with supplementary food.

Physiological attributes as possible selection criteria for milk production 2. Plasma insulin, tri-iodothyronine and thyroxine in bulls

Insulin, thyroxine and tri-iodothyronine concentrations were measured in samples of blood from 175 Friesian bulls, aged between 2 and 7 years, which were being progeny-tested for milk production. Least squares regression coefficients were estimated for these hormone levels on time of day and time after feed at sampling and age of bull. Correlations between hormone levels and Improved Contemporary Comparisons of the bull, a measure of his daughters' milk production, did not differ significantly from zero, suggesting that simple spot estimates of levels of these hormones in bulls would not supply useful predictors of daughters' production.

Physiological attributes as possible selection criteria for milk production 3. Plasma hormone concentrations and metabolite and hormonal responses to changes in energy equilibrium

Plasma hormone concentrations and metabolite responses to changes in energy equilibrium were measured in experiments designed to compare a) Hereford × Friesian with Friesian calves and b) Friesian calves sired by bulls with a high level of Improved Contemporary Comparison with those sired by bulls of a low level. The concentration of thyroxine and triiodothyronine tended to be greater in calves of higher dairy merit. The concentration of growth hormone was largely unrelated to dairy merit in the circumstances studied. The concentration of insulin was greater in Hereford × Friesian than in Friesian calves following feeding and following the injection of propionate. Responses to the injection of insulin and of growth hormone (as measured by changes in the plasma concentration of urea nitrogen, free fatty acids, glucose or the other hormone) were little affected by the level of Improved Contemporary Comparison of a calfs sire.

It was concluded that the thyroid system and the response of insulin to perturbation of energy balance may provide criteria of genetic merit for milk production which are neither age- nor sex-limited.

Contrasting effects of nitrofurans on plasma corticosterone in chickens following administration as a bolus or diet additive

Administration of furazolidone as a bolus dose (8-500 mg/kg), produced a decrease in plasma corticosterone in chickens. In contrast, addition of furazolidone or furaltadone to the diet (0.04% or above, 10 days), increased plasma corticosterone. Pre-treatment with a 200-mg/kg bolus of furazolidone or furaltadone did not affect pentobarbitone anaesthesia time in the birds. In chickens pre-treated with a nitrofuran in the diet, however, pentobarbitone anaesthesia time was significantly less than that in controls. Furaltadone in the diet, produced significant increases in the amount of cytochrome P-450 and the activity of aniline hydroxylase in the liver microsomes. It is suggested that nitrofurans given in the diet stimulated corticosterone biosynthesis in the adrenal glands and induced mixed-function oxidase activity in the liver. Nitrofurans given as a bolus did not produce these effects. Furazolidone (200 mg/kg) produced severe anorexia, which lasted 2 days in T-line birds. The anorexia seemed to be associated with tissue damage in the birds rather than the ensuing adrenal cortical insufficiency.

Inappropriate thyrotrophin secretion, increased dopaminergic tone and preservation of the diurnal rhythm in serum TSH

A patient presented with mild hyperthyroidism, elevated serum T4 and T3, and an inappropriately raised serum thyrotrophin (TSH). There was no evidence of pituitary tumour (alpha-subunit secretion and CT scan of the pituitary were normal). The TSH response to TRH was greater than normal. The elevated TSH was suppressed by oral triiodothyronine (100 micrograms daily for 10 d). The normal diurnal variation of TSH was preserved. Intravenous injection of the dopamine receptor blocking agent domperidone led to a greater than normal elevation in TSH (maximum increments 18-20 mU/l). This increased dopaminergic tone was similar in studies carried out in the morning and late evening. The dopamine agonist bromocriptine (2.5 mg twice daily) failed to suppress serum TSH either acutely or over 6 weeks. The circadian rhythm was unaltered by this treatment. Basal serum prolactin levels were normal, and responded appropriately to TRH, domperidone and bromocriptine. These observations indicate that dopamine does not control the diurnal variation of TSH in nontumoral TSH-mediated hyperthyroidism. The increased dopaminergic tone demonstrated may be secondary to the primary failure of pituitary-thyroid feedback in the condition.

Thyroid function in patients with rheumatic heart disease

Thyroid function was assessed in 94 patients with rheumatic heart disease presenting consecutively to a cardiology clinic. Despite previous reports of an association with autoimmune thyroid disease, abnormal thyroid function occurred no more commonly in this group than would be anticipated in a normal population.

End-organ responses to thyroxine therapy in subclinical hypothyroidism

We studied variables known to change with thyroid hormone status in 18 patients with subclinical hypothyroidism before and during treatment with thyroxine in a dose sufficient to restore the plasma TSH response to TRH to normal. There was an associated increase in both plasma total T4 and free T4 within the normal range but plasma total T3 and free T3 were unchanged. As a result of thyroxine treatment there was a small but significant increase (P less than 0.05) in left ventricular ejection fraction (LVEF) with maximal exercise but no significant changes in LVEF at rest and moderate exercise, continuously monitored mean sleeping heart rate, day/night ratios of urinary sodium excretion, peripheral nerve conduction velocities, fasting serum triglycerides, total cholesterol (TC), high density lipoproteins (HDL) or TC/HDL ratios. On this evidence we do not consider that thyroxine replacement therapy is indicated in patients with subclinical hypothyroidism.

Muscle development in thyroidectomised chickens (Gallus domesticus)

The metabolic and contractile activity of muscle was determined in immature cockerels made hypothyroid by surgical thyroidectomy at 6 weeks of age. Four weeks after thyroidectomy the activity of Mg2+-activated myofibrillar ATPase and total phosphorylase was reduced in the fast-phasic, posterior latissimus dorsi (PLD) and scapulotriceps (ST) muscles. The activities of these enzymes were unaffected in the slow-tonic, anterior latissimus dorsi (ALD) muscle. Thyroidectomy had no effect on length of the muscles studied but reduced the weight of the ALD and ST muscles. These results suggest that hypothyroidism results in a "slowing down" of fast-phasic muscles, although it does not affect the activity of slow-tonic muscles.

The behavior of the triiodothyronine/thyroxine (T3/T4) ratio in normal individuals, and its implications for the regulation of euthyroidism

In order to examine the significance of differences in the triiodothyronine/thyroxine (T3/T4) ratio in the control of euthyroidism in a normal population, we measured the serum T3, T4 and FT4 index (FT4I) in 121 healthy men and 68 women. The correlation between T3 and T4 was poor (r = 0.24), suggesting that most of the natural variation in T3 among normal individuals occurs independently of the T4 level. There was, however, a strong inverse correlation (r = 0.59, p less than 0.001) between T3/T4 ratio and FT4I. This correlation reflected a constancy in mean T3 at different levels of T4 such that the T3 changed by only 0.35 nmol/l (22%) throughout the range of normal T4. Furthermore, the T3/T4 ratios of 48 hypothyroid individuals with subnormal T4 represented a simple extension of the relationship found in the healthy individuals, indicating that the rise in T3/T4 classically associated with falling T4 in primary hypothyroidism is merely part of a continuous process of change which begins in euthyroidism. It is proposed that the relationship between T3 and T4 is finely controlled in healthy individuals in such a way that differences in hormone activity due to the wide range of serum T4 among normals may be buffered by systematic adjustment of the T3/T4 ratio. Those with the highest T4 appear to maintain euthyroidism with a minimal T3/T4 ratio. The remainder, with T4 levels towards the lower limit of normal, are subject to a progressive increase in the T3 fraction and may depend on it to remain euthyroid.(ABSTRACT TRUNCATED AT 250 WORDS)

Delayed recovery of left ventricular function after antithyroid treatment. Further evidence for reversible abnormalities of contractility in hyperthyroidism

Sequential measurements of systolic time intervals, left ventricular dimensions, and the derived indices of contractility were undertaken at rest and during isometric exercise in 15 hyperthyroid patients before, during, and after antithyroid treatment. At rest hyperthyroidism was characterised by a shortened pre-ejection period and increased velocity of circumferential shortening of the left ventricle. During isometric exercise, however, the pre-ejection period increased significantly beyond that predicted for normal subjects, and the velocity of circumferential fibre shortening fell by 30%. In contrast, both the pre-ejection period and the velocity of circumferential fibre shortening were unchanged during exercise after a stable euthyroid state had been achieved for at least three months. Comparison between exercise responses and thyroid status during antithyroid treatment showed that a biochemical euthyroid state may be achieved many weeks before normalisation of contractile response to exercise. These findings support the hypothesis of reversible depression of left ventricular function in hyperthyroidism. Responses at rest principally reflect the peripheral actions of thyroid hormone excess.

Plasma concentrations of luteinising hormone, follicle stimulating hormone, androgen, growth hormone, prolactin, thyroxine and triiodothyronine during growth and sexual development in the cockerel

Changes in concentrations of plasma luteinising hormone (LH), follicle stimulating hormone (FSH), androgen, growth hormone (GH), prolactin (Prl), thyroxine (T4) and triiodothyronine (T3) were measured during growth and sexual maturation in broiler cockerels reared in continuous light to 7 weeks and 14 h light/d thereafter. Concentrations of LH and FSH began to increase between 13 and 15 weeks, while those of androgens increased between 16 and 17 weeks. FSH concentration increased faster than that of LH. Concentrations of GH and Prl were high at 3 weeks; that of GH decreasing progressively between 3 and 14 weeks of age and thereafter remaining low, while that of Prl was low between 5 and 9 weeks, relatively high between 10 and 13 weeks, and then temporarily decreasing before increasing progressively during sexual maturation. Concentrations of T3 and T4 were higher in juvenile than in adult birds.

Natural history of thyroid function in diabetics with impaired thyroid reserve: a four year controlled study

An attempt was made to compare the natural history of thyroid function in 80 diabetics having raised serum TSH concentrations (median 8.9 mU/l, range 5.8-46.3 mU/l) but serum T4 concentrations within the normal range (Group 1), and in 59 diabetics having normal serum TSH (median 1.9 mU/l, range 0.8-4.7 mU/l) and T4 concentrations (Group 2). Thyroid microsomal antibodies were present initially in 65% of patients in Group 1 and 15% of patients in Group 2. By 1981, 59 patients (74%) in Group 1 and 47 patients (80%) in Group 2 had been followed for a mean +/- SD duration of 4.2 +/- 1.8 and 4.2 +/- 1.5 years, respectively. Hypothyroidism developed in 9 patients in Group 1, but none from Group 2. Of patients in Group 1, hypothyroidism developed at a rate of 5% per annum in those with thyroid microsomal antibodies, but only 1% per annum in those without antibodies. Therefore, the risk of development of hypothyroidism is greatest in diabetics having both elevated serum TSH concentrations and thyroid microsomal antibodies and such patients should have regular review of thyroid function. Either risk factor alone appears to be a poor predictor of development of hypothyroidism.

Primary hypothyroidism with grossly elevated plasma total thyroxine and triiodothyronine levels

In an elderly patient with clinical primary hypothyroidism and a raised basal TSH, the serum free thyroxine (fT4), total thyroxine (TT4) and triiodothyronine (TT3) were consistently and paradoxically grossly elevated when measured by radioimmunoassay. In part these hormone levels were due to a high titre of endogenous IgG immunoglobulins which bound T4, T3 and reverse T3 (rT3) and thus caused gross interference in the radioimmunoassays. However, when this methodological interference was removed by using a methanolic extract of the patient's serum, the concentrations of TT4 and TT3 were still grossly elevated. It was only when basal TSH and the concentration of fT4 and fT3 were measured by equilibrium dialysis that these hormone levels were found to be consistent with primary hypothyroidism.

The effect of minor increments in plasma thyroxine on heart rate and urinary sodium excretion

We studied day/night (D:N) patterns of urinary sodium excretion and the 24 hour ambulatory electrocardiogram in seven normal subjects before and during the administration of T4. Thyroxine increased thyroid hormone levels within the normal range and inhibited the plasma TSH response to TRH. This was associated with a significant decrease in D:N sodium excretion (P less than 0.01) and D:N urine flow (P less than 0.01), a significant increase in mean nocturnal heart rate (P less than 0.01), and a lesser increment in mean daytime heart rate (P less than 0.05). These responses to small changes in thyroid hormone levels suggest that the anterior pituitary is not alone in recognising minor thyroid hormone excess. The clinical implication is that some patients with a normal T3 and T4 but an impaired TSH response to TRH might benefit from antithyroid treatment.

Concentrations of triiodothyronine, growth hormone, and luteinizing hormone in the plasma of thyroidectomised fowl (Gallus domesticus)

Surgical thyroidectomy increased (P less than 0.05) the basal concentrations of growth hormone (GH) and luteinizing hormone (LH) in the plasma of 10- to 12-week-old domestic fowl. The administration of thyrotrophin releasing hormone (TRH) (100 micrograms, sc) increased (P less than 0.01) the GH concentration in both intact and thyroidectomised birds. The magnitude of the TRH-induced increase in GH level was greater (P less than 0.01) in thyroidectomised birds than in intact controls. Although TRH had no effect on LH secretion in the controls, it induced a small (P less than 0.05) rise in the plasma LH level in thyroidectomised birds. In both the intact and thyroidectomised birds the LH concentration was enhanced (P less than 0.05) following the administration of LH-releasing hormone (LH-RH) (20 micrograms, sc). The increase in the LH level by LH-RH in the thyroidectomised birds was greater (P less than 0.001) than that in the intact controls. Plasma GH concentrations were unaffected by LH-RH treatment. These results suggest that thyroid hormones inhibit the secretion of LH and GH in birds. In thyroidectomised birds low levels of immunoreactive triiodothyronine (T3)-like material were measurable in the circulation, despite the absence of regenerated thyroid tissue. The administration of TRH (100 micrograms, sc) did not enhance the plasma level of this material in thyroidectomised birds, whereas plasma T3 concentrations were enhanced in intact birds following TRH treatment. These results suggest that the T3 immunoreactive substance in thyroidectomised birds is extrathyroidal in origin.

Thyroid hormones in the sudden infant death syndrome (SIDS)

Results are presented of serum total T4, T3, and TSH measurements on 92 patients. There are 34 infants exhibiting the sudden infant death syndrome, 36 in control group 1, who are matched both for age of infant and for duration of storage of specimen, and 22 post-mortem sera from non-SIDS deaths. There is no significant difference between the groups for total T4 measurements, but there is a highly significant elevation of both total serum T3 and TSH in the SIDS group compared with control group 1. It is suggested that the TSH elevation may be due to a post-mortem effect, but the T3 results appear to confirm and extend the recent publication of Chacon et al [1]. Evidence of one case of a near-SID that subsequently died is presented, demonstrating that disturbances of thyroid function tests occurred in this patient before death.

Thyroid function tests in thyroid and nonthyroid disease

Modern day evaluation of thyroid disorders requires a combination of accurate clinical judgement and reliable, sensitive, and specific thyroid functions tests. Principle among the latter are thyroxine (T4) 3, 5, 3'-triiodothyronine (T3), and thyroid-stimulating hormone (TSH). Also playing an important role in special situations are free thyroxine, an assessment of bound and unbound thyroid-binding globulin, TRH stimulation, long-acting thyroid stimulator (LATS), antibodies to thyroid hormone and to thyroid receptors. Basic to interpretation of these tests in the clinical setting is a comprehension of the relationship of the hypothalamus, the pituitary, and the thyroid gland as well as a knowledge of the peripheral metabolism of thyroxine and triiodothyronine. The role of each of these laboratory tests in the evaluation of hyper- and hypometabolic states, their alteration in nonthyroid and other endocrine disorders, and the effects of environmental and physiological factors on these tests are reviewed.

Antithyroid effect of chlorpropamide?

1 The relationship between plasma chlorpropamide concentration and thyroid function was examined in 87 maturity onset diabetic patients receiving chronic therapy. 2 Although plasma chlorpropamide concentration was weakly negatively correlated with serum thyroxine (r = 0.33, P less than 0.01) the mean serum thyroxine and thyrotrophin (TSH) were not different from that of a matched control group of diabetics treated with diet alone. 3 Serum thyroxine was negatively correlated with the duration of diabetes in both groups. 4 These results suggest that chlorpropamide does not have a clinically significant antithyroid effect.

Abnormal left ventricular function in hyperthyroidism: evidence for a possible reversible cardiomyopathy

We assessed the effects of exercise and beta-adrenoceptor blockade on left ventricular ejection fraction (LVEF) measured by radionuclide ventriculography in nine patients with uncomplicated hyperthyroidism. Patients were studied in both the hyperthyroid and euthyroid states. The hyperthyroid state was characterized by a high LVEF at rest but--paradoxically--by a significant fall (P less than 0.01) in LVEF during exercise. At the same workload and at the same heart rate, patients had a restoration of the normal rise in LVEF during exercise when they were euthyroid. The LVEF was greater during exercise (P less than 0.02) when the patients were euthyroid than when they were hyperthyroid. Pretreatment with propranolol caused similar reductions in resting LVEF in the hyperthyroid and euthyroid states; the drug attenuated the rise in LVEF during exercise when the patients were euthyroid, but did not influence the exercise-induced reduction in LVEF in hyperthyroidism. The abnormal left ventricular function observed during exercise in hyperthyroidism suggests a reversible functional cardiomyopathy, independent of beta-adrenoceptor activation, that is presumably a direct effect of an excess in circulating thyroid hormones.

Nadolol and potassium iodide in combination in the surgical treatment of thyrotoxicosis

With the two aims of rapidly reducing circulating thyroid hormone levels and controlling the symptoms of thyrotoxicosis, we have prepared 17 thyrotoxic patients for subtotal thyroidectomy, using a combination of potassium iodide administered for 10 days and the long acting beta-adrenoceptor antagonist nadolol. All 17 patients had normal serum thyroxine levels after 10 days of such treatment although 10 still showed elevation of serum tri-iodothyronine and considerable elevation in the most severely toxic patient. All patients were, however, clinically euthyroid preoperatively. Nadolol was administered once daily, hence avoiding the problems of drug administration in the immediate postoperative period, and plasma nadolol concentrations were high throughout the perioperative period. Serum thyroxine and tri-iodothyronine levels were significantly lower and reverse tri-iodothyronine levels higher 24 h postoperatively than before operation. All patients remained stable throughout the perioperative period. We conclude that this regimen has a number of advantages in the preparation of patients for thyroidectomy, in reducing the degree of thyrotoxicosis, in convenience of drug administration and in ensuring adequate circulating concentrations of beta-adrenoceptor antagonist whilst still retaining a relatively short preoperative phase of drug treatment.

Left ventricular function in hypothyroidism. Responses to exercise and beta adrenoceptor blockade

The effects of exercise and beta adrenoceptor blockade on left ventricular function were assessed in eight patients with hypothyroidism before and during thyroxine replacement treatment. Left ventricular ejection fraction, measured by radionuclide ventriculography, was reduced in hypothyroid patients at rest and on exercise. The rise in ejection fraction with exercise was, however, similar in both groups. Pretreatment with intravenous propranolol reduced the ejection fraction at rest 9% in both hypothyroid and euthyroid patients and reduced the rise on exercise. Directional changes in a second index of myocardial contractility based on the shape of the ventricular volume curve paralleled the changes in the ejection fraction. Left ventricular function is therefore reversibly depressed by thyroid hormone deficiency but responses to exercise and beta adrenoceptor blockade are normal. There is no evidence of altered adrenergic sensitivity in the control of myocardial contractility in hypothyroidism.

Does calcitonin cause hypocalcaemia after thyroidectomy?

Plasma calcitonin, parathyroid hormone, total thyroid hormones and calcium were measured in 6 patients before, during and after thyroidectomy for hyperthyroidism. In 4 patients, plasma calcium fell postoperatively by 0.23--0.46 mmol/l, but there was no change in calcitonin or parathyroid hormone levels. In one patient, in whom there was a postoperative fall in plasma calcium of 0.55 mmol/l, thyroid hormones rose to a peak at 1 h and calcitonin to a peak at 12 h after resection. However, the rise in calcitonin occurred 8 h after the initial decrease in plasma calcium. In this patient, parathyroid hormone levels showed a slight rise only. It is concluded that, while thyroid hormones and calcitonin may leak from the damaged thyroid remnant after surgery, it is unlikely that calcitonin is important in the production of postoperative hypocalcaemia. However, impaired parathyroid hormone secretion may be a contributing factor.

What is the significance of raised plasma TSH levels after thyroid surgery?

Thyroid function was assessed prospectively for five years in 73 patients treated surgically for Graves's disease. No patient developed hypothyroidism after the sixth postoperative month, despite the presence of raised plasma TSH levels in 70 per cent of euthyroid patients at the end of the first year. Indeed, in those with evidence of temporary hypothyroidism (low T4, raised TSh at 3 months but normalisation of T4 at 6 months) plasma TSH continued to fall for up to three years. The majority (6) of patients developing recurrent hyperthyroidism did so within the first year, but in one of three patients who relapsed subsequently, plasma TSH had been elevated at one year. Plasma TSH cannot be used to predict thyroid status following surgery for Graves' disease. Although regular review remains necessary, it should not include measurement of TSH unless this is needed to confirm the validity of a low thyroxine level after the third postoperative month and before starting permanent replacement therapy.

Nadolol in thyrotoxicosis

1 Twenty outpatients with thyrotoxicosis received the non-selective beta-adrenoceptor antagonist nadolol as sole treatment for 3 weeks. 2 Clinical improvement as measured by reduction in thyrotoxicosis therapeutic index occurred during the first week of treatment and was continued thereafter, and was accompanied by a significant reduction in serum T3 and elevation of serum reverse T3. 3 As measured by reduction in exercise heart rate, during chronic dosing nadolol 160 mg once daily produced blockade of beta-adrenoceptors for 12 h in all patients and 24 h in all but 2. 4 Wide interindividual variability was noted in steady state plasma nadolol concentrations, in part related to age and renal function. 5 Steady state plasma nadolol concentrations were related to reduction in heart rate.

Nocturnal natriuresis in hyperthyroidism

We measured urine flow and the renal excretion of total solute, sodium, potassium and calcium in eleven patients with hyperthyroidism before and after treatment. Mean nocturnal sodium excretion was significantly greater (P less than 0.05) during hyperthyroidism and was unaccompanied by any significant alterations in day time or 24-h values. As a result of this nocturnal natriuresis in hyperthyroidism significant changes were noted in the ratios of day/night sodium excretion (P less than 0.005) and urinary flow (P less than 0.05). The change in ratio of day/night sodium excretion resulting from treatment of hyperthyroidism was shown to correlate significantly with the change in plasma total triiodothyronine (r=0.73, P less than 0.01). Twenty-four hour urinary calcium output was significantly greater (P less than 0.02) in hyperthyroidism but there was no significant alteration in the day/night pattern of excretion.

Propranolol in the surgical treatment of hyperthyroidism, including severely thyrotoxic patients

The perioperative course of 44 hyperthyroid patients prepared for surgery with propranolol alone, including 11 with severe thyrotoxicosis was compared to that of 20 euthyroid patients prepared for surgery with carbimazole. Conventional propranolol at a dosage of 160 mg/day was frequently insufficient to produce a high degree of beta-adrenergic blockade, particularly in severely thyrotoxic patients. A greater than 25 per cent reduction in sitting pulse rate was associated with a high degree of beta-blockade. The clinical course of patients with mild or moderate thyrotoxicosis was similar to that of the patients prepared with carbimazole. In contrast, the course of severely thyrotoxic patients was complicated and, in addition to a higher preoperative propranolol dosage, these patients commonly required supplemental propranolol after operation. Although thyroid crisis did not occur in any patient, we cannot recommend the use of propranolol alone for the severely thyrotoxic patient.

Direct and correlated responses to selection for plasma thyroxine levels in mice

Selection was carried out in mice for concentration of thyroxine hormone (T4) in plasma of males at 11 weeks of age over seven generations. Selection was practised for high level in two replicate lines and for low level in two replicate lines, and there was an unselected control. There was a response in both directions, and the divergence of 12·4 ng/ml observed in generation seven was equivalent to about 20% of the base population mean or nearly one phenotypic standard deviation. The realised heritability was 9%.

Plasma thyroxine level had a repeatability of 0·54 when two measurements were made 24 h apart. The responses made at 11 weeks in males were also evident in both males and females at 5 weeks. Plasma tri-iodo thyronine (T3) concentrations showed a correlated response almost as large, relative to the mean level, as that in T4.

Positive correlated responses were observed in total weights of the litter at 12 days, and in individual weights at 3, 6 and 9 weeks, the responses in the early weights being greater relative to their mean. The results suggest that the correlated weight changes were due to genetic responses in maternal characteristics, probably milk production, rather than individual growth.

Altered plasma protein binding of drugs in thyroid disease

The plasma protein binding of propranolol and warfarin was studied in vitro by ultrafiltration in hyper- and hypothyroid patients both before and after treatment. The degree of binding of propranolol was significantly decreased in hyperthyroid patients and increased in hypothyroid patients, and was negatively correlated with serum thyroxine and the free thyroxine index. The plasma protein binding of warfarin was also decreased in hyperthyroid patients, but was unchanged in hypothyroid patients. These results suggest that the binding of both acidic and basic drugs may be altered by thyroid disease.

Lack of a relationship between concentrations of plasma luteinising hormone, thyroxine and prolactin at nine week's of age and subsequent egg production in the domestic hen

1. The concentrations of plasma luteinising hormone (LH), thyroxine and prolactin were measured in about 200 birds from each of two homogenous strains of White Leghorn hens at 9 weeks of age and related to subsequent egg production. 2. Within each strain, no relationships were found in individual birds between the concentrations of the plasma hormones and subsequent egg production after 90, 180 and 270 d of laying. 3. Single measurements of plasma LH, thyroxine or prolactin before the onset of lay do not appear to be useful criteria for the selection of egg-laying strains.

Paracetamol pharmacokinetics in thyroid disease

The absorption, distribution and elimination of oral paracetamol have been studied in patients before and after treatment of thyrotoxicosis (n = 7) and hypothyroidism (n = 4). Absorption was faster in patients with untreated thyrotoxicosis than when subsequently euthyroid. The peak paracetamol concentration, however, was lower in thyrotoxic patients due to an apparent increase in the total body clearance and a shorter plasma half-life. Both absorption and elimination rates were reduced in hypothyroid patients, but were not significantly different from the euthyroid results. When estimated using a two compartment model the total volume of distribution and the hybrid distribution rate constants were unrelated to thyroid status, but the apparent volume of the central compartment was significantly greater in the thyrotoxic group. These changes in drug disposition may contribute to differences in drug response seen in thyroid disease.

Combination of potassium iodide and propranolol in preparation of patients with Graves' disease for thyroid surgery

We assessed the efficacy of the combination of propranolol and potassium iodide in the preparation of patients with Graves' disease for thyroid surgery. Potassium iodide was given orally in a dose of 60 mg three times a day for 10 days before operation in 10 patients who were already receiving propranolol. In contrast to previous experience with either drug used singly, the combined regimen caused a significant fall in mean serum total thyroxine and triiodothyronine to levels in the euthyroid range before operation (P less than 0.001). There was also a significant fall (P less than 0.05) before operation and transient rise after operation in serum reverse triiodothyronine. These preliminary results suggest that the combination of potassium iodide and propranolol may prove to be the optimum preoperative preparation for patients with Graves' disease.

Occult thyrotoxicosis: a correctable cause of "idiopathic" atrial fibrillation

Serum total thyroxine, triiodothyronine and thyrotropin response to thyrotropin-releasing hormone were measured in 75 consecutive patients presenting to a cardiology clinic with atrial fibrillation with no obvious cardiovascular cause. A lack of response of serum thyrotropin to thyrotropin-releasing hormone, indicative of thyrotoxicosis, was found in 10 patients (13 percent), not all whom had raised serum thyroid hormone levels. These 10 patients were predominantly male, had no clinical signs of thyrotoxicosis and a relative excess of nonpalpable autonomous thyroid nodules demonstrated with scintigraphy. Eight of the 10 patients had reversion to stable sinus rhythm after treatment with iodine-131 or carbimazole, either spontaneously or after direct current cardioversion. It would appear that clinically occult thyrotoxicosis can be identified consistently only with the thyrotropin-releasing hormone test and is the cause of "idiopathic" atrial fibrillation in a significant proportion of patients.

Propranolol, triiodothyronine, reverse triiodothyronine and thyroid disease

Propranolol alone was given to sixteen hyperthyroid, and concomitantly with thyroxine therapy to ten hypothyroid patients. Following treatment of the hyperthyroid group for 1-2 weeks there was a significant decrease in serum triiodothyronine (T3) which correlated with the plasma propranolol steady state concentration. The serum reverse T3 (rT3) rose significantly. Weight loss ceased in this group while weight gain occurred in patients who had a marked fall in serum T3. One patient with T3 toxicosis went into remission. The reduction in serum T3 was maintained in six patients receiving propranolol for more than 1 month. In the hypothyroid group the mean serum T3 level achieved with 0.15 mg thyroxine per day was significantly lower than in a control group who did not receive propranolol. In five patients following propranolol withdrawal there was a significant rise in T3, a fall in rT3 and TSH, and weight loss. Propranol may therefore have a clinically significant and direct action on the peripheral conversion of thyroxine to T3 and rT3.

How often should patients be reviewed after treatment with iodine-131 for thyrotoxicosis?

Six to 18 years after treatment with iodine-131 for thyrotoxicosis 69 euthyroid patients with raised serum thyrotrophin (TSH) concentrations (mean 25.0 +/- SE 2.0 mU/l) and 61 with normal concentrations (mean 4.0 +/- 0.2 mU/l) were included in a prospective five-year follow-up study beginning in 1972. During this period 13 patients from the original group with raised serum TSH concentrations became hypothyroid. In contrast it was five years before hypothyroidism developed in a single patient from the group with normal serum TSH concentrations in 1972, although raised concentrations were recorded in 19 of these patients during the study.

Scottish Immunoassay Support Service Quality Control scheme for thyroxine, triiodothyronine, and digoxin assays: analysis of first 18 months' experience

Summary Initial experience of the Scottish Immunoassay Support Service Quality Control scheme for thyroxine (T4), triiodothyronine (T3), and digoxin is analysed.

For T4, radioimmunoassay (RIA) methods gave values close to the all-method mean. Competitive protein binding (CPB) kits gave values significantly higher (by 12%) in one and lower (by 10%) in another, probably due to the extraction of interfering substances such as non-esterified fatty acids or thyroid hormone binding proteins. The range of between-batch precision of individual laboratories was 10·8–47·5% (mean 17·8%) over the clinically relevant range. It was particularly poor at levels below the lower limit of the normal range.

For T3 RIA, kit methods gave significantly higher values than independent methods although recovery of exogenous T3 was approximately quantitative with both. Cross reaction of T4 in T3 assays was insignificant. The range of between-batch precision for individual laboratories was 11·4–35·5% (mean 21·9%), and was poorest at levels of 1 nmol/l or less.

For digoxin RIA, Lanoxitest γ gave significantly higher values than other methods, and over-recovered exogenous digoxin. The range of between-batch precision was 13·8–35·2% (mean 21·6%), and was poorest at levels of 1 nmol/l or less.

The distribution of liquid human serum specimens at ambient temperature was satisfactory for quality control of T4, T3, and digoxin RIA but not for T4 by the Thyopac 4 method. Ox serum was unsuitable for certain T4 RIA methods.

Thyroid function after surgical treatment of thyrotoxicosis. A report of 100 cases treated with propranolol before operation

We assessed thyroid function for 12 months after subtotal thyroidectomy in 100 tyrotoxic patients treated with propranolol alone before and immediately after operation. The operation proved safe, with low morbidity. Suppression of the hypothalamic-pituitary-thyroid axis, present in the majority one month after operation, was evidenced by normal or low levels of serum total tri-iodothyronine and thyroxine, but absent or subnormal serum thyrotropin response to thyrotropin-releasing hormone. Eighty patients were euthyroid at 12 months. Three patterns of thyroid function were observed in this group between the first and 12th months: normal serum total tri-iodothyronine, thyroxine and thyrotropin levels at all stages (20 patients); normal serum total tri-iodothyronine and thyroxine, but raised thyrotropin levels on one or more occasions (40 patients); and temporary hypothyroidism (20 patients). Of the remaining 20 patients, permanent hypothyroidism developed in 14, and six relapsed. Postoperative thyroid function was related to the estimated weight of the thyroid remnant.

The behaviour of thyroid hormones in an infant with untreated neonatal thyrotoxicosis

The clinical course from birth and serial measurements of serum T3, T4 and TSH in an infant with untreated neonatal thyrotoxicosis are reported. The thyroid hormone levels fell exponentially with time at rates very much slower than those previously reported for the maternally-transmitted thyroid stimulating antibody generally thought to cause the disorder. Steady physiological levels of thyroid hormones were achieved after 110 days (serum T3 = 3.4 NMOL/L, T4 = 118 nmol/l). TSH first rose to a measurable level after about 90 days.

A rapid and precise sequential saturation radioimmunoassay for thyroxine

A radioimmunoassay for the measurement of total thyroxine in unextracted serum or plasma is described. The assay is performed according to the sequential saturation principle in less than 4 h. The entire assay is carried out at room temperature. An antiserum of high affinity was used as binder, ammonium 8-anilino-1-naphthalene-sulphonate as displacing agent, and activated charcoal as adsorbent in the separation step. The standard curve was linear in the range 0-136 nmol/l serum. The precision in terms of SD was nearly the same through-out this range. Estimates of within-assay SD varied from 1.3 to 4.1 and between-assay SD from 0 to 3.3 nmol/l. The recovery of thyroxine added to normal plasma was 100% and the sensitivity was 6 nmol/l. Mean thyroxine concentration in plasma from young bulls was 92 nmol/l. The assay appears to be very well suited for experimental purposes when high precision is essential.