Quantification of thyroxine and 3,5,3'-triiodo-thyronine in human and animal hearts by a novel liquid chromatography-tandem mass spectrometry method.

Assaying tissue T3 and T4 would provide important information in experimental and clinical investigations. A novel method to determine tissue T3 and T4 by HPLC coupled to mass spectrometry is described. The major difference vs. previously described methods lies in the addition of a derivatization step, that is, to convert T3 and T4 into the corresponding butyl esters. The yield of esterification was Ì´ 100% for T3 and 80% for T4. The assay was linear (r>0.99) in the range of 0.2-50 ng/ml, accuracy was in the order of 70-75%, and the minimum tissue amount needed was in the order of 50 mg, that is, about one order of magnitude lower than observed with the same equipment (AB Sciex API 4000 triple quadrupole mass spectrometer) if derivatization was omitted. The method allowed detection of T3 and T4 in human left ventricle biopsies yielding concentrations of 1.51±0.16 and 5.94±0.63 pmol/g, respectively. In rats treated with different dosages of exogenous T3 or T4, good correlations (r>0.90) between plasma and myocardial T3 and T4 concentrations were observed, although in specific subsets different plasma T4 concentrations were not associated with different tissue content in T4. We conclude that this method could provide a novel insight into the relationship between plasma and tissue thyroid hormone levels.

Minimal changes of thyroid axis activity influence brain functions in young females affected by subclinical hypothyroidism.

There is evidence of an association between thyroid hormones (TH) alterations and mental dysfunctions related to procedural and working memory functions, but the physiological link between these domains is still under debate, also for the presence of age as a confounding factor. Thus, we investigated the TH tuning of cerebral functions in young females affected by the borderline condition of subclinical hypothyroidism (SH) and in euthyroid females of the same age. The experiment consisted in the characterization of the affective state and cognitive abilities of the subjects by means of specific neuropsychological questionnaires, and of brain activity (EEG) in resting state and during the passive viewing of emotional video-clips. We found that SH had i) increased anxiety for Physical Danger; ii) better scores for both Mental Control and no-working-memory-related functions; iii) association between anxiety for Physical Danger and fT4 levels. Thus, in young adults, SH increases inward attention and paradoxically improves some cognitive functions. In addition, self-assessed questionnaires showed that SH had a greater susceptibility to unpleasant emotional stimulation. As for EEG data, SH compared to controls showed: i) reduction of alpha activity and of gamma left lateralization in resting state; ii) increased, and lateralized to the right, beta2 activity during stimulations. Both results indicated that SH have higher levels of arousal and greater susceptibility to negative emotion than controls. In conclusion, our study indicates that minimal changes in TH levels produce subtle but well-defined mental changes, thus encouraging further studies for the prediction of pathology evolution.

Thyroid hormone, amiodarone therapy, and prognosis in left ventricular systolic dysfunction.

BACKGROUND: Amiodarone protects patients with left ventricular systolic dysfunction (LVSD) against serious arrhythmias, but it also has numerous side effects on non-cardiac organs, such as the thyroid. Indeed, amiodarone may inhibit the peripheral conversion of T4 into T3. Pathologically reduced serum levels of T3 - the so-called "low T3 syndrome" (LOWT3) - increase mortality in patients with LVSD and not on amiodarone. AIM: The aim of the study was to examine the relationship between thyroid hormone status, amiodarone therapy, and outcome in a population with LVSD. MATERIAL/ SUBJECTS AND METHODS: A total of 2344 patients with LVSD and free of overt hyper- and hypothyroidism were enrolled. The population was divided into 4 groups: group 1 (LOWT3 and amiodarone therapy, no.=126), group 2 (isolated amiodarone therapy, no.=74), group 3 (isolated LOWT3, no.=682), group 4 (controls, no.=1462). RESULTS: Kaplan-Meier curves showed, after a mean follow-up of 31 months, increased total and cardiac mortality in groups 1 (30% and 20%, respectively), 2 (23%, 11%), and 3 (22%, 12%) compared to group 4 (total mortality log-rank 82.8, p<0.0001; cardiac mortality log-rank 63.1, p<0.0001). At Cox analysis, adjusted for several clinical variables, survival was reduced in groups 1 and 3 compared to group 4. Group 2 had a similar mortality to group 4, although the number of patients was too limited to accurately assess the effect of amiodarone on long-term prognosis. CONCLUSIONS: LOWT3 exerts an adverse impact on prognosis in LVSD, which is not influenced by concomitant amiodarone therapy.

Thyroid disrupting effects of low-dose dibenzothiophene and cadmium in single or concurrent exposure: New evidence from a translational zebrafish model.

Thyroid hormones (THs) are major regulators of biological processes essential for correct development and energy homeostasis. Although thyroid disruptors can deeply affect human health, the impact of exogenous chemicals and in particular mixture of chemicals on different aspects of thyroid development and metabolism is not yet fully understood. In this study we have used the highly versatile zebrafish model to assess the thyroid axis disrupting effects of cadmium (Cd) and dibenzothiophene (DBT), two environmental endocrine disruptors found to be significantly correlated in epidemiological co-exposure studies. Zebrafish embryos (5hpf) were exposed to low concentrations of Cd (from 0.05 to 2 µM) and DBT (from 0.05 to 1 µM) and to mixtures of them. A multilevel assessment of the pollutant effects has been obtained by combining in vivo morphological analyses allowed by the use of transgenic fluorescent lines with liquid chromatography mass spectrometry determination of TH levels and quantification of the expression levels of key genes involved in the Hypothalamic-Pituitary-Thyroid Axis (HPTA) and TH metabolism. Our results underscore for the first time an important synergistic toxic effect of these pollutants on embryonic development and thyroid morphology highlighting differences in the mechanisms through which they can adversely impact on multiple physiological processes of the HPTA and TH disposal influencing also heart geometry and function.

The role of thyroid hormone in the pathophysiology of heart failure: clinical evidence.

Thyroid hormone (TH) has a fundamental role in cardiovascular homeostasis in both physiological and pathological conditions, influencing cardiac contractility, heart rate (HR), diastolic function and systemic vascular resistance (SVR) through genomic and non-genomic mediated effects. In heart failure (HF) the main alteration of thyroid function is referred to as "low-triiodothyronine (T3) syndrome" (LT3S) characterized by decreased total serum T3 and free T3 (fT3) with normal levels of thyroxine (T4) and thyrotropin (TSH). Even if commonly interpreted as an adaptive factor, LT3S may have potential negative effects, contributing to the progressive deterioration of cardiac function and myocardial remodeling in HF and representing a powerful predictor of mortality in HF patients. All these observations, together with the early evidence of the benefits of T3 administration in HF patients indicate that placebo-controlled prospective studies are now needed to better define the safety and prognostic effects of chronic treatment with synthetic TH in HF.

Expression of thyrotropin and thyroid hormone receptors in adipose tissue of patients with morbid obesity and/or type 2 diabetes: effects of weight loss.

OBJECTIVE: Increased thyroid-stimulating hormone (TSH) and FT(3) levels are often found in clinically euthyroid obese individuals. Information on thyroid gene expression in human adipose tissue is scarce. The objective of this study was to measure the expression of the TSH receptor (TSHR) and the thyroid hormone receptor (TRalpha1) genes in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) in obese individuals and to test the effect of weight loss on these genes. STUDY DESIGN AND PARTICIPANTS: This study is a prospective study involving 107 obese (body mass index (BMI)=46+/-8 kg m(-2), 52 with type 2 diabetes or impaired glucose tolerance) and 12 lean nondiabetic participants. A total of 27 obese patients were restudied 1 year after gastric bypass surgery. Total RNA was extracted from SAT and VAT obtained at baseline from all participants, and from SAT in obese patients post surgery. RESULTS: Circulating TSH and FT(3) levels were 170 and 36%, respectively, higher in obese patients than in controls. In SAT, TSHR and TRalpha1 were reduced in the obese by 67 and 33%, respectively, regardless of glucose tolerance. A similar trend was found in VAT. Post surgery, a BMI decrease of 33% was associated with a decrease in TSH and FT(3) levels and with a 150 and 70% increase in SAT of TSHR and TRalpha1, respectively. CONCLUSION: In both subcutaneous and visceral fat, the thyroid gene expression (especially TSHR) is reduced in obesity. The reversal of these changes with major weight loss and the reciprocal changes in plasma TSH and FT(3) levels suggest a role for adipocytes in the regulation of TSH and thyroid hormones.

Thyroid fine needle aspiration: how to improve clinicians' confidence and performance with the technique.

Studies from single institutions report an acceptable accuracy rate for thyroid fine needle aspiration (FNA). However, FNA accuracy is much lower in many other centers in Europe and the USA and large multicenter studies indicate that the clinicians' confidence in the FNA technique remains low. One explanation for this is that there is an excess of inadequate and indeterminate findings for a follicular nodule at FNA cytology. In a University Hospital with large and qualified experience on thyroid nodule diagnosis, a review of 320 slides with an FNA diagnosis of indeterminate follicular nodule from different minor Italian Hospitals led to a different diagnosis in 61%. Since ancillary thyroid imaging may be overutilized and only a few authors report a proportion of excised nodules lower than 10%, we suspect that use of the FNA procedure is suboptimal. Several techniques are reported to improve the performance of thyroid FNA. Among these are tumor markers and large needle aspiration biopsy (LNAB). Immunodetection of the tumor marker galectin-3 has been evaluated by large multinational studies. Analysis of LNAB specimens reduces the number of inadequate FNA findings, improves the diagnostic determination of indeterminate follicular FNA findings and represents a better substrate for the determination of galectin-3. Therefore, we propose that clinical practice guidelines reflect these adjuvant techniques to thyroid FNA in order to improve selection criteria for thyroid nodule surgery.

Role of serum carrier proteins in the peripheral metabolism and tissue distribution of thyroid hormones in familial dysalbuminemic hyperthyroxinemia and congenital elevation of thyroxine-binding globulin.

To investigate the role of thyroxine-binding globulin (TBG) and albumin in the availability of thyroid hormones to peripheral tissues, comprehensive kinetic studies of thyroxine (T4) and triiodothyronine (T3) were carried out in eight subjects with familial dysalbuminemic hyperthyroxinemia (FDH), in four subjects with inherited TBG excess, and in 15 normals. In high-TBG subjects, the reduction of T4 and T3 plasma clearance rates (by 51% and 54%, respectively) was associated with normal daily productions; T4 and T3 distribution volumes were significantly reduced. In FDH subjects T4 clearance was less reduced (by 31%) than in high TBG; consequently T4 production rate was significantly increased (by 42%); T4 and T3 distribution volumes and T3 clearance rate were unchanged. Increased T3 peripheral production in FDH (by 24%) indicates that T4 bound to abnormal albumin is more available to tissues than T4 carried by TBG, thus suggesting an important role of albumin in T4 availability to the periphery.

Serum thyroglobulin measurement: clinical background and main methodological aspects with clinical impact.

It is worldwide recognized that circulating thyroglobulin (Tg) measurement represents a fundamental tool in the follow-up of patients affected by differentiated thyroid cancer (DTC). In the last American and European Consensus Conferences, a surveillance guideline has been extended to the use of thyrotropin (TSH)-stimulated Tg levels for thyroidectomized patients without clinical evidence of residual tumor with Tg below 1 microg/l during TSH suppression. Therefore, sensitivity of the methods is critical to detect small amounts of Tg and/or to observe minimal changes in Tg concentration in the management of DTC patients. It has been proposed that only methods providing the greatest distinction between the lower limit of euthyroid reference range (approximately 3.0 microg/l) and the functional sensitivity limit (at least 1 microg/l) of the assay may offer a suitable clinical sensitivity for detecting small amounts of functioning thyroid tissue in TSH-suppressed state (1 g of normal thyroid tissue results in a serum Tg of approximately 1 microg/l when TSH is normal and about 0.5 microg/l when TSH is suppressed). In the last 30 years sensitivity of Tg measurements has been greatly improved, nowadays methods can achieve very good analytical and functional sensitivity to give reliable results also in the very low concentration range (between 0.1 and 1 microg/l). In addition, with the introduction of fully automated assays, results can be readily available to the clinician while patients are still in the ambulatory area. However, despite the large clinical use of Tg measurement, wide differences (by threefold) still remain between results produced in different laboratories due to poor standardization, heterogeneity of circulating Tg, interference from auto-antibodies, differences in the epitope recognition by antibodies used in the assays.

Thyroid nodule evaluation: what have we really learned from recent clinical guidelines?

Recent guidelines for the evaluation of thyroid nodules clarify the diagnostic algorithm while also reporting important differences. The performance of fine needle aspiration (FNA) for cytological examination follows serum TSH determination and thyroid ultrasonography. Thyroid scintigraphy is recommended following a low TSH value and/or FNA yielding an indeterminate follicular cytology. The use of thyroid ultrasonography is the source of some controversy: though it is recommended as a principal first test, its real-time use to guide FNA ranges from routine to only following an FNA yielding an inadequate or nondiagnostic cytological result. In clinical practice, the proportion of physicians utilizing ultrasonography, scintigraphy and FNA varies and frequently deviates from recommended guidelines. The development of guidelines is necessary to bring about consistency and optimization to the diagnostic work-up of thyroid nodules. It is likely that novel diagnostic procedures, such as molecular markers, large needle aspiration biopsy and thyroid imaging with tracers beyond conventional radioactive iodine or (99m)Tc pertechnetate, will lead to improved performance and implementation of guidelines.

3,5,3'-Triiodothyronine deprivation affects phenotype and intracellular [Ca2+]i of human cardiomyocytes in culture.

OBJECTIVE: A decrease in plasma T3 concentration is a frequent finding in patients with heart failure. However, the role of this 'low T3 syndrome' on disease evolution has never been clarified. As phenotypic and functional cardiomyocyte impairments are alterations that correlate with the failing myocardium, we studied the long-term effects of T3 deprivation on human cardiomyocyte structure and calcium handling. METHODS: Atrial cardiomyocytes and myocardial tissue were cultured with or without 3 nM T3. Microscopical examination of structural features was followed by analysis of alpha-sarcomeric actinin and sarcoplasmic reticulum calcium ATP-ase (SERCA-2) content. Calcium handling was studied by [Ca2+](i) imaging. RESULTS: When stimulated with cyclopiazonic acid, a SERCA-2 inhibitor, T3-deprived cardiomyocytes showed significantly faster (P=0.03) and more transient (P=0.04) increases in [Ca(2+)](i) than T3-supplemented cells. Moreover, in the T3-free cultures a significantly lower number of cells (P=0.003) responded to caffeine, a typical activator of sarcoplasmic reticulum Ca(2+)-release channel. T3-deprived cardiomyocytes also presented altered morphology with larger dimensions than T3-supplemented cells (P < 0.0001). Additionally, in T3-deprived samples alpha-sarcomeric actinin and SERCA-2 protein levels were reduced to 65.6 +/- 3% (P < 0.0001) and 74.1 +/- 4% (P=0.005), respectively, when compared with the T3-supplemented group. CONCLUSIONS: Our data show that human cardiomyocyte calcium handling and phenotype are strongly influenced by T3 suggesting important implications of the 'low T3 syndrome' on the progression of heart failure.

Acute effects of amiodarone administration on thyroid function in patients with cardiac arrhythmia.

Because little has been published on early effects of treatment with amiodarone on thyroid function, we studied serum total and free thyroid hormone, reverse T3, and TSH levels in patients with cardiac arrhythmias during the first 10 days of treatment with a loading dose of amiodarone by iv infusion. Twenty-four patients were enrolled in the study. A standardized loading regimen for the i.v. infusion of amiodarone was used. The protocol provided the i.v. infusion of 20 mg/kg per day on day 1, the i.v. infusion of 10 mg/kg per day on day 2, then 600 mg/day per os for 7-10 days, and finally, in patients chronically treated with the drug, the dose was gradually reduced to 400-200 mg/day per os. Total and free concentrations of T4 tended to progressively and significantly increase (P < 0.0001 repeated measures ANOVA) starting from the fourth day of therapy, whereas total T3 decreased from the second day progressively (P < 0.0001) throughout the study; free T3 did not significantly change. TSH levels early and significantly (P < 0.001, by ANOVA) increased throughout the study, starting from the first day of therapy and reaching at 10 days a value 2.7 times higher than the basal value. Reverse T3 levels progressively and significantly (after 2 days of treatment) increased and paralleled the TSH values, reaching at the 10th day a value about 2 times higher than basal value. In conclusion, our data suggest that after i.v. treatment with amiodarone: 1) TSH is the first hormone to change significantly followed by reverse T3, T4, and T3; 2) the progressive fall of T3 levels reflects an inhibition of the peripheral conversion of T4 to T3; 3) the observed later increase of total and free T4 levels may be explained by a contribution of direct thyroidal stimulation by TSH and/or by a reduction in T4 clearance.

Atrial natriuretic peptide is not degraded by the lungs in humans.

In an attempt to identify and quantify the sites of atrial natriuretic peptide (ANP) degradation, particularly the lungs, a new tracer method to study ANP metabolism in vivo in humans was developed and applied to patients with left ventricular dysfunction. Thirteen male, normotensive, cardiac patients with different degrees of left ventricular myocardial involvement were enrolled in the study. The study protocol required constant infusion (3 patients) or bolus injection (10 patients) of 125I-labeled ANP just upstream of the right atrium and blood sampling from different sites (pulmonary artery, aorta, inferior vena cava, and femoral vein) during the hemodynamic study. Data analysis was based on a kinetic model consisting of three blocks in series (right heart, lungs and left heart, and periphery) supplied by the same plasma flow (plasma cardiac output). Plasma levels of native ANP were measured with a sensitive and specific immunoradiometric assay method. ANP values measured in the aorta (163.9 +/- 144.8 pg/mL, n = 80) were superimposable on those measured in the pulmonary artery (161.8 +/- 136.5 pg/mL, n = 80). Negligible extraction of 125I-labeled ANP was found in the lungs and left heart block (on average 0.08 +/- 3.92%), whereas the peripheral block extraction (46.2 +/- 7.8%) accounted for almost total hormone removal from the blood (whole body extraction was 46.4 +/- 6.6%). ANP metabolic clearance rate (3.11 +/- 1.48, range 1.4-6.8 L/min) declined with the progression of left ventricular dysfunction (plasma cardiac output 3.46 +/- 1.08, range 1.2-5.7 L/min), and a close correlation between metabolic clearance rate and cardiac output was evident. Our data suggest that lungs do not extract, or extract only very small amounts, of labeled ANP administered iv to patients with different degrees of left ventricular myocardial involvement, and whole body extraction of labeled ANP remains relatively stable with the progression of disease, and the large reductions in clearance values observed in our patients can be ascribed mainly to the reductions in cardiac output.

Evidence that atrial natriuretic peptide tissue extraction is not changed by large increases in its plasma levels induced by pacing in humans.

Atrial natiurectic peptide (ANP) is a cardiac hormone with a very short plasma half-life, which plays an important role in a variety of clinical conditions associated with an increase in pressure and/or volume overload on the heart. The MCR of the hormone is considered to represent a stable parameter, reflecting the uptake and degradation rate of ANP by the periphery, only scarcely affected by rapid oscillations of circulating levels. To evaluate the extent to which MCR is affected by rapid and large variations of circulating levels of the hormone, we measured MCR in five patients with different degrees of myocardial function (from normal to severely impaired), in whom changes in ANP levels were induced by atrial and/or ventricular pacing. Cardiac output was simultaneously measured by thermodilution to calculate whole body extraction of ANP. During constant i.v. infusion of [125I]ANP, the hormone MCR was determined both under basal conditions (at tracer equilibration, 20-30 min after the start of infusion) and during atrial and ventricular pacing. Pacing maneuvers, begun 50 min after the start of infusion, induced a marked and rapid increase in endogenous plasma ANP values in all patients (on the average, 3,7-fold compared to basal values; range, 1.8-5.68), whereas corresponding values of [125I]ANP only minimally changed. The MCR of ANP (3.62 +/- 1.06 L/min, mean +/- SD) slightly decreased (by repeated measures ANOVA, P = 0.0458) during atrial and ventricular pacing procedures (3.35 +/- 1.03 and 3.15 +/- 0.74 L/min, respectively), reaching a mean value of 88.7 +/- 9.0% compared to basal. The small decrease in MCR could be almost completely ascribed to hemodynamic factors; indeed, basal cardiac output (5.76 +/- 1.70 L/min) was found, on the average, to be slightly decreased during atrial and ventricular pacing (5.28 +/- 1.46 and 5.16 +/- 1.33 L/min, respectively), and so whole body extraction of the hormone, measured before pacing (50.0 +/- 12%), remains stable throughout the study period (50.4 +/- 10.6% and 49.6 +/- 10% during atrial and ventricular pacing, respectively). Our findings demonstrate that degradative mechanisms involved in ANP clearance are not saturable at least for acute elevations of ANP plasma levels up to 3-5 times the basal level.

Turnover studies on cardiac natriuretic peptides: methodological, pathophysiological and therapeutical considerations.

Cardiac natriuretic peptide hormones (ANP and BNP) are synthesized and secreted by the heart, producing several biological effects, such as natriuresis, vasorelaxation, hypotension, and neuromodulation. Extensive studies conducted in both animals and humans have documented that cardiac natriuretic peptides (CNPs) are secreted into the circulatory system via the coronary sinus into the right atrium, and then rapidly degraded and removed from the blood by plasma proteases and specific clearance receptors. Usually, studies of CNPs kinetics have been carried out following an experimental protocol in which labeled or unlabeled hormone is administered (by constant infusion or bolus injection) and the corresponding concentration of the hormone is measured in peripheral venous blood. However, when a uniform intravascular concentration throughout artero-venous vessels is lacking due to the very rapid clearance of the substance being studied (such as CNPs), the classical compartmental or none compartmental approach may not be suitable for interpreting the experimental data. In this case, a more physiological circulatory model, which does not assume a uniform intravascular distribution of the hormone and comprises several anatomo-functional blocks arranged in a series and supplied by the same flow (cardiac output) should be adopted. Different experimental designs (infusion or bolus injection) as well as multiple sampling sites (aorta and pulmonary artery, inferior vena cava, femoral vein) were used in ANP kinetic studies. Using a circulatory approach, ANP has been demonstrated to be rapidly distributed and degraded; in healthy subjects about 50% of ANP secreted into the right atrium is extracted by the peripheral tissues during the first pass throughout the body. Since CNPs have important fluid-volume regulatory features, it has been postulated that they also play a key role in volume homeostasis in several pathophysiological states, such as congestive heart failure. Indeed, a markedly altered degradation and distribution of ANP in patients with cardiac failure who show a resistance to its natriuretic effects, even in those on the early stage of clinical disease, whose CNPs plasma levels are in the normal range, have been demonstrated. Recent studies indicate that some drugs, by inhibiting the degradation of CNPs by plasma proteases and can thus affect CNP kinetics, may be useful in the treatment of arterial hypertension and cardiac failure.

Chromatographic identification in serum of endogenously radioiodinated thyroid hormones after iodine-131 whole-body scintigraphy in the follow-up of patients with differentiated thyroid carcinoma.

Patients with differentiated thyroid cancer (DTC) are conventionally followed with serial 131I whole-body scintigraphy (WBS) and serum thyroglobulin (hTg) assay. Given the 15%-20% incidence of discordant results, we developed a sensitive and specific procedure for monitoring such patients, based on the assumption that 131I uptake, even if too low to be detected by 131I WBS, could be assayed in serum as thyroid products (hTg, T3 and T4) endogenously labeled with 131I. Our study included 125 patients routinely monitored for tumor recurrence or for the persistence of functioning thyroid tissue after complete primary treatment for DTC (surgery and 131I ablation of remnants). A plasma sample, taken 72 hr after administering 131I for WBS was fractionated on a Sephadex-G25 superfine column by first eluting all of the radioactive species except the thyroid hormones and then the radioiodothyronines. The sensitivity and specificity of chromatography in detecting functioning thyroid tissue after primary treatment for DTC were 98.4% and 100% (accuracy 99.2%), respectively, versus 90.6% and 95.1% for 131I WBS (accuracy 92.8%) and 60.9% and 100% for hTg (accuracy 80%). Combining chromatography with serum hTg gave the highest gains in diagnostic performance (100% for all parameters). This chromatographic method can be used in addition to conventional procedures in the follow-up of patients with DTC and represents a highly sensitive test for assessing the results of 131I ablation of postsurgical remnants.

Diagnostic performance of a new highly sensitive thyroglobulin immunoassay.

The determination of serum thyroglobulin (Tg) is commonly used for detecting the presence of residual thyroid tissue or cancer recurrence in patients treated for differentiated thyroid cancer (DTC). The aim of the study was to evaluate the performance characteristics of a recently introduced fully automated chemiluminescent immunoassay, based on four monoclonal antibodies and which produces results in 40 min. Analytical sensitivity (0.01 micro g/l) was computed from 20 replicates of the zero calibrator and of the 'Tg-free' sample pool. Functional sensitivity (0.1 micro g/l at 20 coefficients of variation percent) was determined from the imprecision profile obtained by assaying ten serum pools. The reliability of the measurements in the low concentration range (Tg<1 micro g/l) has been checked by progressive dilution with the 'Tg-free' serum of a sample pool at 5.27 micro g/l; measured values were very close to the expected values (recovery 100-133%).Cut-off at the 99th percentile in DTC stage I 'disease-free' treated patients (n=53) was 0.16 micro g/l. Tg measurement in basal conditions during L-thyroxine suppression therapy and 5 days after recombinant human TSH stimulation was performed in 22 patients with DTC. In 80% of patients with basal Tg<0.1 micro g/l (12/15), Tg remained<0.1 micro g/l after stimulation, and in all of these Tg was<1 micro g/l. Our results have indicated the optimal analytical and clinical performance of this Tg immunoassay and encourage further studies on larger populations of patients with DTC.

Is the low tri-iodothyronine state a crucial factor in determining the outcome of coronary artery bypass patients? Evidence from a clinical pilot study.

The cardiovascular system is an important target for thyroid hormones. The present study evaluates the changes affecting thyroid hormone metabolism during and 6 days after coronary artery bypass and their relationship with the post-operative outcome of the patients. Thirty-three patients were enrolled in the study; their thyroid hormone profiles were determined at 13 sampling points during surgery and for 6 days afterwards. Serum total tri-iodothyronine (T3) and free T3 (FT3) concentrations decreased significantly after surgery (P<0.001) and they remained significantly low until the end of the study. Free thyroxine (FT4) and T4 declined significantly immediately after surgery (P<0.05 for FT4, P<0.001 for T4) but they returned to baseline values (24 h and 96 h post-surgery respectively). Serum reverse T3 increased remarkably 36 h after surgery (P<0.001) and remained significantly higher than the baseline value throughout the study. A relevant finding was that the days of post-operative hospitalization (10+/-3 days, means+/-S.D.) was inversely correlated with the slope of the recovery of T3 concentration (P<0.001) or with the area under the plasma curves of T3 (P=0.024, time range 72-144 h) and the FT3/FT4 ratio (P=0.037, time range 72-144 h) during the post-operative period. Our data suggest a prolonged reduction of T4 to T3 conversion in patients undergoing cardiac surgery and indicate that the recovery period is the most critical in the evaluation of a possibly successful approach for T3 substitutive therapy.

Serum thyroid hormone concentrations and recovery of TSH secretion after excision of autonomously functioning thyroid nodules.

Serum concentrations of TSH, TT4, TT3 and rT3 were monitored for one month after excision of ten autonomous thyroid adenomas which had suppressed TSH secretion. Basal serum TSH levels start to increase between 30 hr and 20 days after surgery reaching normal and steady levels by the 24 day. Serum TT3 concentrations rapidly decrease in the first 20 hr to values near the lower limit of the normal range. Thereafter TT3 levels change little until pituitary TSH secretion recovers. Serum TT4 levels also fall, but much more slowly than TT3. Rising TSH levels stimulate residual extranodular thyroid tissue secretion of both TT3 and TT4. However, serum TT3 levels rise more rapidly than TT4 levels. Preoperative serum concentrations of both TT4 and TT3 are related directly to the time required until the beginning of the postoperative rise in TSH levels, and inversely with the maximal postoperative serum TSH concentration achieved. Throughout the study period, for all patients, serum TSH concentrations were inversely related to serum TT4 concentrations. These data suggest that, although the time required until the onset of recovery of TSH secretion is directly related to preoperative levels of TT4 and TT3, the regulation of postoperative TSH levels is dependent upon serum TT4 levels. Also, the serum TT3 levels constant at the lower limit of the normal range before recovery of TSH secretion, and the preferential rise in serum TT3 concentrations associated with rising TSH secretion, may prevent or abbreviate temporary postoperative hypothyroidism.