Serum triiodothyronine and reverse triiodothyronine concentrations after surgical operation

Influence of medications on thyroid function in dogs: An update

Erroneous thyroid function test results can occur because of drugs that alter thyroid hormone physiology in one or more aspects, including synthesis, secretion, distribution, and metabolism. Research since publication of the last review in the Journal of Veterinary Internal Medicine (JVIM) 20 years ago has evaluated the effects of amiodarone, zonisamide, inhalant anesthetics, clomipramine, trilostane, and toceranib on thyroid function tests in the dog. In addition, recent work on the effects of glucocorticoids, sulfonamides, phenobarbital, and nonsteroidal anti-inflammatory drugs will be reviewed. Awareness of these effects is necessary to avoid misdiagnosis of hypothyroidism and unnecessary treatment.

Triiodothyronine attenuates neurocognitive dysfunction induced by sevoflurane in the developing brain of neonatal rats

BACKGROUND

Whilst concerns have been raised about the detrimental effects of general anaesthetics on the brain's development and function in the young, reports have indicated that thyroid hormones are able to promote neurogenesis in the developing brain. This present study aimed to investigate the effects of triiodothyronine (T3) on the neonatal rat brain, following sevoflurane exposure.

METHODS

Postnatal day 7 (P7) ratpups were treated with Triiodothyronine (T3) (1 µg/100 g body weight, i.p. injection, once/day for 3 days) after 2% sevoflurane exposure for 6 h. They were sacrificed at either P7 (immediately), P15 or P30 and their brains were harvested to assess cell death, proliferation in the hippocampus, N-methyl-D-aspartate (NMDA) receptor subunit A and B, and a post-synaptic protein (PSD-95 in the hippocampus,). Neuro-behavioral changes in other cohorts between P27 and P30 were evaluated with Morris water maze and open field tests.

RESULTS

Sevoflurane exposure caused cell death and suppressed the proliferation of astrocytes and neurons, as well as the dendritic growth of neurons in the hippocampus which were all reversed by the administration of T3. Moreover, cognitive function, including learning, memory, and adaptability to a new environment, were impaired by sevoflurane exposure, which was also negated by T3 treatment. Furthermore, sevoflurane decreased the expression of NMDA receptor subunits NR2A and NR2B, as well as PSD-95 in the hippocampus at P15 and those effects of sevoflurane were abolished by T3 administration.

CONCLUSIONS

A potential therapeutic role of T3 in protecting general anesthetic induced neuronal injury in the developing brain is likely to occur through enhancing expression of PSD-95 and the NMDA NR2A and NR2B expression.

Acute Neuroendocrine Profile in Predicting Outcomes in Severe Traumatic Brain Injury: A Study from a Tertiary Care Center in South India

BACKGROUND

Pituitary dysfunction following severe traumatic brain injury (sTBI) is significant and may be correlated with the outcomes.

AIMS AND OBJECTIVES

This study aimed to evaluate the early changes in pituitary hormone levels after sTBI and to correlate with outcomes in terms of severity and mortality.

METHODS

This was a prospective, observational study, involving consecutive patients of 16-60 years, with sTBI (Glasgow Coma Scale GCS < 9) presenting to the hospital within 24 h of trauma. Demographic and clinical data were collected. Serum samples were collected in the morning (08-10 am) on day 1 and day 4 for cortisol, thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), and prolactin (Chemiluminescence immunoassay). Outcome was assessed in terms of mortality (which included both immediate and at 3 months) and Glasgow outcome scale at 3 months.

RESULTS

54 patients were studied. Mean cortisol on day 4 was 28.5 μg/dL in alive patients and 13.7 μg/dL in patients deceased at 3 months (P < 0.001). Patients who were deceased at 3 months had significantly lower T3 on day 4 (0.973 vs 1.4 ng/dL) and lower T4 (8.1 μg/L vs 6.1 μg/dL) as compared to patients who survived (P = 0.049 and 0.005, respectively). Acute phase TSH on day 4 levels were significantly lower in patients deceased at 3 months. There was no significant difference in the prolactin levels.

CONCLUSION

Day 4 cortisol, T3, T4, and TSH correlated with the outcomes at 3 months and hence have predictive value post-sTBI.

Low triiodothyronine syndrome as a predictor of poor outcomes in patients undergoing brain tumor surgery: a pilot study

Object

A low triiodothyronine (T3) state is highly prevalent and is associated with a poor prognosis in critically ill patients. The authors investigated, in patients undergoing brain tumor surgery, the direct association of a perioperative low T3 syndrome with clinical outcomes and also with symptoms of depression and anxiety.

Methods

Ninety consecutive patients (71% women, median age 55 years), on admission for brain tumor surgery, were evaluated for sociodemographic and clinical characteristics. Their thyroid function profile was assessed on the morning of brain tumor surgery and on the morning after brain tumor surgery. Patients with free T3 concentrations of 3.1 pmol/L or less were considered to have low T3 syndrome. The patients were evaluated for symptoms of depression and anxiety using the Hospital Anxiety and Depression Scale (HADS) before and after surgery and for clinical outcomes using the Glasgow Outcome Scale (GOS) at discharge.

Results

After brain tumor surgery, free T3 concentrations decreased (p < 0.001) and the proportion of patients with low T3 levels increased from 38% to 54% (p = 0.02). Lower preoperative (rho = 0.30, p = 0.004) and postoperative (rho = 0.33, p = 0.002) free T3 concentrations correlated with low GOS scores at discharge. Preoperative low T3 syndrome (OR 5.49, 95% CI 1.27–23.69, p = 0.02) and postoperative low T3 syndrome (OR 8.73, 95% CI 1.49–51.21, p = 0.02) both increased risk for unfavorable clinical outcomes (GOS scores < 5) at discharge, after adjusting for age, sex, histological diagnosis of brain tumor, preoperative functional impairment, previous treatment for brain tumor, and depressive symptoms. Preoperative low T3 syndrome increased the risk for preoperative (HADS-depression subscale score ≥ 11; OR 4.12, 95% CI 1.16–14.58, p = 0.03) but not postoperative depressive symptoms independently from sociodemographic and clinical factors.

Conclusions

Low T3 syndrome is a strong independent predictor of unfavorable clinical outcomes and depressive symptoms, and its diagnosis and preoperative management should be considered in patients undergoing neurosurgery for the treatment of brain tumors.

The spectrum of thyroid disorders in systemic lupus erythematosus

To study the spectrum of thyroid disorders in systemic lupus erythematosus (SLE). Hundred SLE patients as per American Rheumatology Association(ARA) classification criteria underwent clinical examination, including assessment of disease activity (SLEDAI) and laboratory evaluation for serum triiodothyronine (T3),free thyroxine (FT4), thyroid stimulating hormone (TSH), antithyroperoxidase (TPO) antibody and antithyroglobulin (TG) antibody. Hundred age- and sex-matched apparently healthy individuals served as control. Thirty-six (36%) lupus patients had thyroid dysfunction when compared to 8 (8%) of controls and all of them were women. Primary hypothyroidism was the commonest dysfunction in 14 (14%), while subclinical hypothyroidism and subclinical hyperthyroidism was seen in 12 (12%) and 2 (2%), respectively. Eight (8%) had isolated low T3 consistent with sick euthyroid syndrome. Eighteen (50%) of thyroid dysfunction were autoimmune in nature (autoantibody positive) and rest 18 (50%) were non-autoimmune. Euthyroid state with the elevation of antibodies alone was seen in 12 (12%) of the lupus patients. In contrast, only 5 (5%) of controls had primary hypothyroidism and 3 (3%) had subclinical hypothyroidism, while none had hyperthyroidism. SLEDAI score and disease duration were compared between lupus patients with thyroid dysfunction to those with normal thyroid function. A statistically significant association was found between SLEDAI and thyroid dysfunction of sick euthyroid type.SLE disease duration had no statistically significant association with thyroid dysfunction. Prevalence of thyroid autoantibodies in lupus patients was 30% when compared to 10% of controls. Ninety-six (96%) of the SLE patients were ANA positive, while 4 (4%) of them were ANA negative but were anti-Sm antibody positive. There were no suggestions of any other autoimmune endocrine diseases like diabetes or Addison's disease (clinically and on baseline investigations) in our lupus cohort and hence no further work up was done for these diseases. Thyroid disorders are frequent in SLE and are multifactorial with a definite higher prevalence of hypothyroidism as well as thyroid autoantibodies.

Divergent changes of serum 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine in patients with acute myocardial infarction

The serum levels of thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (reverse T3, rT3), thyroxine-binding globulin and thyroid-stimulating hormone have been monitored in 13 patients with acute myocardial infarction. The major changes recorded were a transient decrease in T3 and a transient increase in rT3. They reached a nadir and a peak, respectively, within three days. A conceivable explanation for these alterations is that the monodeiodination of T4 is diverted from the activating pathway (T4 to T3) to the inactivating pathway (T4 to rT3).

Some hormonal influences on glucose and ketone body metabolism in normal human subjects

Control of glucose and ketone body metabolism is integrated by a variety of hormones. Insulin is the major anabolic hormone, and its actions are antagonized by rapidly acting catabolic hormones, such as glucagon and the catecholamines, and by others such as cortisol, growth hormone and the thyroid hormones, which generally have more delayed effects. In the normal human subject, the effects of catabolic hormones to raise blood glucose are limited by a compensatory increase in insulin secretion, and these effects are enhanced in insulin deficiency. Hyperketonaemic actions of the catabolic hormones may result from increased supply of non-esterified fatty acids from lipolysis, although glucagon has a major direct action to increase ketogenesis at the liver. As expected, these actions are also restricted in normal humans by the compensatory rise in insulin secretion. Hyperketonaemia does, however, occur with adrenaline (epinephrine) and noradrenaline (norepinephrine), even in the presence of mildly elevated insulin concentrations. These catecholamines may assume particular importance in mobilization of lipid fuels in milder forms of stress, when insulin secretion is normal or mildly increased. In severe stress, when there is catecholamine-induced suppression in insulin secretion, lipolytic and hyperketonaemic effects of all the catabolic hormones may be manifest. Starvation in humans also results in diminished insulin secretion and increased catabolic hormone secretion. The relative importance of individual hormones in lipid mobilization during starvation is uncertain, although glucagon, growth hormone, noradrenaline and, possibly, dopamine may all play a part.

L-thyroxine therapy attenuates the decline in serum triiodothyronine in nonthyroidal illness induced by hysterectomy

It is controversial whether the administration of thyroid hormone to patients with nonthyroidal illness has any beneficial effect. Two groups of patients undergoing abdominal hysterectomy under the same general anesthesia were studied. Group A consisted of 15 women taking chronically l-thyroxine therapy (1.8 mug/kg daily), and group B (control) consisted of 16 apparently healthy euthyroid women taking placebo. Thyroid hormones, cortisol, and interleukin (IL)-6 were measured 1 day before and 1, 2, 3, and 6 days after surgery. Total triiodothyronine (TT(3)) decreased to a significantly greater degree (P <.05) and for a longer period of time in group B than in group A. The significant increase of reverse T(3) (rT(3)) noted early in group B failed to reach the baseline levels until the end of the study, whereas in group A, rT(3) returned to the preoperative values by day 2. Both groups had similar free thyroxine (FT(4)) at baseline. FT(4) increased significantly at day 1 and remained significantly elevated throughout the postoperative period in group B only. Serum TT(4), thyroid-stimulating hormone (TSH), and cortisol did not change significantly in either group. In all patients, IL-6 increased significantly to a peak value at day 1, showing a slow decrease thereafter. A stronger negative correlation was found between T(3) and IL-6 in group B than in group A (r = -.66, P <.0001 v r = -.38, P <.001, respectively) and a strong positive correlation was observed between rT(3) and IL-6 in group B only (r =.57, P <.001). The long-term treatment with T(4) seems to attenuate the decrease of serum T(3), which occurs during the development of nonthyroidal illness postoperatively. The elevation of IL-6 accounted for a greater proportion of the variations of the T(3) and rT(3) in the control group B than in the T(4)-treated group A.

Coordinated transcription of key pathways in the mouse by the circadian clock

In mammals, circadian control of physiology and behavior is driven by a master pacemaker located in the suprachiasmatic nuclei (SCN) of the hypothalamus. We have used gene expression profiling to identify cycling transcripts in the SCN and in the liver. Our analysis revealed approximately 650 cycling transcripts and showed that the majority of these were specific to either the SCN or the liver. Genetic and genomic analysis suggests that a relatively small number of output genes are directly regulated by core oscillator components. Major processes regulated by the SCN and liver were found to be under circadian regulation. Importantly, rate-limiting steps in these various pathways were key sites of circadian control, highlighting the fundamental role that circadian clocks play in cellular and organismal physiology.

Low T3 syndrome with asynchronous changes of TT3 and rT3 values in laparoscopic cholecystectomy

Non-thyroidal illnesses, such as surgical stress, are associated with abnormal metabolism of thyroid hormones. However, the potential impact of variable surgical procedures remain to be elucidated. In order to evaluate the effect of mild surgical stress upon thyroid function, TT4, TT3, rT3 and TSH were measured in twenty-two patients undergoing laparoscopic cholecystectomy before (Stage 1), during (Stages 2-5), at the recovery room (Stage 6) and 24h postoperatively (Stage 7). The values of TSH remained within the normal limits with transient changes during the study period. Similarly, TT4 values displayed normal variations within the normal range without reaching a statistically significant difference during the study period. A decrease of TT3 values was detected early at stage 2 during induction of anaesthesia. TT3 remained at low levels during the perioperative period, and a further decrease was observed 24 h postoperatively. The above profile of thyroid hormone metabolism, reflects a low-T3 syndrome in patients undergoing laparoscopic cholecystectomy. Interestingly, there was a tendency for rT3 to increase and it reach its highest value 24h postoperatively with the difference being statistically significant (p<0.05). The asynchronous distribution of rT3 and TT3 might be attributed to multifactorial influences.

Elevated serum interleukin-6 and decreased thyroid hormone levels in postoperative patients and effects of IL-6 on thyroid cell function in vitro

We studied a wide variety of surgical patients to determine whether serum levels of interleukin-6 (IL-6) or tumor necrosis factor-alpha (TNF-alpha) correlate with the changes in serum thyroid hormone levels of the postoperative period. Surgical procedures were divided into minor surgery (cholecystectomy, n = 12), moderate surgery (colorectal cancer and stomach cancer, n = 54), and extensive surgery (esophageal cancer or pancreatic cancer, n = 6). One day after surgery, serum free T3 levels decreased in all 3 groups when compared to the preoperative values; serum free T4 levels did not change regardless of surgical procedure. Serum TSH levels decreased significantly 1 day after surgery in the groups of moderate and extensive surgery. Serum levels of IL-6 increased 12 h after surgery and began to decrease gradually thereafter. There was no change in serum levels of TNF-alpha before and after surgery. The increment of serum IL-6 was dependent on the surgical procedures: the more extensive the surgery, the greater the increase in serum IL-6. Serum free T3 and free T4 levels were inversely correlated with the serum levels of IL-6. To further examine whether IL-6 is responsible for alteration of thyroid hormone production, cultured porcine thyroid follicles were exposed to 0 to 20 ng/ml of recombinant human IL-6 for 24 to 48 h. Then, type 1 5'-deiodinase activity (T4 to T3 converting enzyme), iodide uptake, and thyroid peroxidase (TPO) activity were measured. Our in vitro experiments showed no effect of IL-6 on these parameters. In summary, surgical procedure can cause elevation of serum IL-6 and decrease in serum free T3 levels. However, IL-6 alone does not appear to be a strong candidate for alteration of thyroid hormone production including T3 generation from T4.

The effects of infusion of amino acids alone or in combination with glucose and fat on thyroid hormone and other metabolite interactions in surgery

The effects of infusion of amino acids alone or in combination with carbohydrate and lipid on triiodothyronine (T3) and reverse triiodothyronine (rT3) status, substrate availability and metabolism in surgically-stressed and clinically euthyroid patients were examined. The characteristic post-operative decline in T3 concentration was observed in all patient groups (p < 0.001) (8 patients in each group). However, infusion with amino acids alone retarded the decline in T3; the decrease was lower than those found in the controls and the mixed nutrition group and restoration of T3 values was incomplete, even by the sixth post-operative day. The pattern of increase in rT3 was similar in all 3 patient groups. However, the T3/rT3 ratio dropped to its lowest level on day 1 in the control group and the mixed infusion group (p < 0.001), with a complete restoration by the sixth post-operative day, whereas in the amino acids infused group the ratio was lowest on day 2 (p < 0.001) and was still significantly low by day 6 compared with the pre-operative value (p < 0.001). The findings, in the group infused with amino acids of a less prominent hyperglycaemia, with the significant slowing of T3 response and the significant correlation of rT3 with the plasma glucose, indicate a link between hyperglycaemia and the thyroid hormone response to surgical trauma. No correlations were found between thyroid hormone or urea concentrations, and the blood concentrations of free fatty acids, 3-hydroxybutyrate, or urea; or between thyroid hormone and the percentage of total urea nitrogen excretion. Results show that the changes in fat metabolism after operation are unlikely to be responsible for the changes in T3 and rT3. In conclusion, whereas the post-operative response of T3 concentration can be partially modified by the nutrition regimen employed, that of rT3 is largely related to surgical stress.

Acute development of low T3 syndrome and changes in pituitary-adrenocortical function after elective cholecystectomy in women: some differences between young and elderly patients

From two groups of female patients (young group: 15 patients aged less than 25 years; elderly group: 15 patients aged more than 65 years) who were subjected to cholecystectomy, blood samples were obtained on the day before surgery, on the day of surgery before premedication and after waking up from anaesthesia and also on days 1, 3 and 7 after surgery. In aliquots of sera the levels of TSH, ACTH, thyroxine (T4), triiodothyronine (T3), reverse triiodothyronine (rT3) and cortisol were estimated with the aid of radio-immunoassay (RIA). The differences between the young and elderly subjects were evaluated with the aid of four different statistical tests. Though no changes in the level of T4 were found, the level of T3 was significantly decreased and that of rT3 was significantly increased on Day 1 after surgery. However, the decrease of T3 was expressed more significantly in the young group and, in addition, an increase of rT3 in the same group was found even before premedication. The level of TSH showed a sharp increase at the end of surgery, which was expressed more in the young group. Though no differences between groups were observed in a sharp peak of the ACTH level during surgery, the increase of cortisol level in the elderly group was significantly higher and remained so during the post-operative period.

A general overview of amiodarone toxicity: its prevention, detection, and management

Although amiodarone is a highly effective antiarrhythmic agent, it has a high incidence of side effects, some of which can be serious or even lethal. With close monitoring, side effects can be found in essentially all patients, but fortunately most of these are mild and well tolerated. Furthermore, many will respond to dosage reduction in a relatively short period of time, ie, days to weeks, which is remarkable considering the long period of time amiodarone has been shown to persist in tissues. There is reasonable evidence that toxicity, particularly the early toxic manifestations with large loading dosages, can be favorably modified by reducing the dosage. Similarly, reducing the maintenance dosage will, in most instances, reduce or eliminate most toxic manifestations. The mechanisms of toxic effects are uncertain, but suggestive evidence exists for and against both an immunologic reaction and an intracellular lysosomal lipoidosis. Principles of use of amiodarone should include individualizing administration of dosages for each patient due to the unusual pharmacokinetic properties of this drug and continuous long-term attempts at using the lowest effective dosage. There are no definite tests that predict amiodarone efficacy or toxicity, but the serum level can be used as a rough guide of absorption and distribution in the attempt to minimize the maintenance dosage. No guidelines regarding screening tests for toxicity can be made at this time since great variability in these tests has been reported, and no evidence exists for their benefit in preventing adverse effects to amiodarone. However, follow-up testing at the intervals noted in the package insert are reasonable and important. The possibility of interactions with drugs already reported and with others not yet reported should always be kept in mind, and appropriate monitoring for clinical evidence of toxicity due to the concomitantly used drugs should be undertaken. Amiodarone can have a tremendous beneficial effect in the proper circumstances, but it is a drug that should command utmost respect because of its side effects and requires constant vigilance from any physician wishing to use it.

Possible steroid withdrawal syndrome following short Synacthen test--a personal report

Symptoms not attributable either to disease rebound or to adrenal suppression have been reported both in patients receiving steroids when long-term therapy has been stopped and in normal volunteers after single oral doses of prednisolone or intravenous equivalents. This so-called steroid withdrawal syndrome remains poorly understood. It has not previously been reported following exposure to increased levels of endogenous steroids after diagnostic administration of synthetic adrenocorticotrophic hormone (ACTH). The author's personal experience of an apparent steroid withdrawal reaction following a short Synacthen test is described. It is suggested that as yet unidentified individual factors must play a role in determining whether steroid withdrawal symptoms occur. Closer observation of other subjects after the Synacthen test might reveal other instances of steroid withdrawal symptomatology following this common diagnostic procedure.

Thyroid hormone alterations in patients with shock and injury

Serum concentrations of total T3 and T4, free T4, rT3, TSH, TBG and cortisol were measured on arrival in hospital in 33 adult injured patients, 26 of whom were received directly from the accident. Serum cortisol levels and all thyroid indices, except TBG, were altered substantially by injury. Compared with values from 57 healthy volunteers, statistically significant (P less than 0.01) decreases were found in the mean serum free and total T4 concentrations and the rT3 level. Similarly significant (P less than 0.001) increases were seen in the mean serum T3, TSH and cortisol concentrations. Repeated assessment of thyroid function in six patients suggested a biphasic response to injury by TSH, T3 and rT3. The first phase was of short duration (1-2 h). Serum levels of TSH and T3 were above normal, and rT3 was decreased. These data suggest participation by the thyroid in the 'fight-or-flight' response to life-threatening stress. The second phase was fully established 6-18 h after injury and was characterized by reductions in serum TSH, T3 and total and free T4 and a rise in rT3. This pattern persisted throughout the 2-week period of measurement. Thus, as in other critical illnesses, the 'low T3' syndrome is common in severely injured patients. However, changes in thyroid hormone metabolism after injury are of greater intensity and longer duration.

Prolactin, growth hormone and thyrotropin-thyroid hormone secretion during stress states in man

Changes in hormone secretion and/or metabolism almost constantly accompany stressful events. The hormonal response to stress is directly related to the intensity of the stimulus, and greatly depends on the individual's perception of potentially stressful situations. Hypoglycaemia, surgery and exercise represent physical, metabolic and psychological stressful events where the activation of the endocrine system plays a great role. These endocrine responses also include the secretion of GH and prolactin, but the response pattern varies with the stimulus. Hypoglycaemia, exercise and surgery are potent stimuli to GH and prolactin release, both in men and women. The available data suggest that prolactin is more responsive than GH to surgical stress, whereas physical exercise and hypoglycaemia preferentially stimulate GH secretion. Prolactin levels during hypoglycaemia rise solely when symptomatic neuroglycopenia is achieved. By contrast, prolactin and GH responses to purely psychological stress are rarely seen, although some forms of reproductive stress may potentiate prolactin release in women. A teleologically satisfactory rationale for the acute GH and prolactin rise in response to these stressful stimuli is not clearly apparent in man. No definite metabolic activity of prolactin on intermediate metabolism has been demonstrated, although prolactin is mildly diabetogenic. The known metabolic actions of GH do not appear to be critical during surgery or acute hypoglycaemia, although GH probably participates in the regulation of metabolic homeostasis during chronic hypoglycaemia and chronic exercise. Changes in secretion and/or metabolism of hypothalamic neurotransmitters can increase the secretion of GH by increasing the secretion of GHRH or by decreasing the secretion of somatostatin. The prolactin rise is brought about by either a decrease in dopamine activity, an increased secretion of a hypothetical PRF, or by both mechanisms. Since multiple neuronal pathways converge on the hypothalamus from many other parts of the brain, the pronounced effects of hypoglycaemia, exercise and surgery on the secretion of GH and prolactin also reflect the action of different and complex neural inputs on the activity of the hypothalamic-pituitary axis. However, the morpho-functional mapping of these excitatory pathways still remains incomplete. TSH secretion is tightly regulated by the negative feed-back mechanism exerted by thyroid hormones. The small changes in TSH level observed during surgery and physical exercise seem to reflect mainly alterations in peripheral T4 metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)

Surgery in patients with endocrine dysfunction

Patients with diabetes mellitus, thyroid dysfunction, and adrenal suppression from exogenous steroid therapy frequently undergo surgery. An understanding of the pathophysiology of these disorders enables the medical consultant to have valuable input into the preoperative evaluation and perioperative management of these patients. This article serves as a practical guide in following such patients through surgery, thereby decreasing overall morbidity and mortality.

Per- and postoperative changes in the concentration of serum thyreotropin under general anaesthesia, compared to general anaesthesia with epidural analgesia

In 18 patients scheduled for lower intraabdominal surgery (hysterectomy), changes in thyreotropin (TSH) thyroxine (T4), triiodothyronine (T3) binding of thyroid hormones to plasma proteins (T3-uptake) and glucose in serum were evaluated. In eight patients afferent neurogenic impulses from the surgical area were blocked (Th4-S5) with bupivacaine 0.5% infused continuously into the epidural space from the start of the operation until 6 h postoperatively. All patients received general anaesthesia with thiopentone, pethidine, pancuronium and nitrous-oxide plus oxygen. The patients receiving epidural analgesia had no increase in plasma-TSH, compared to the other group, which had a significant (P less than 0.05) increase peroperatively. The patients receiving epidural analgesia were pain-free and the normal stress-induced increase in plasma-glucose was abolished. Concerning T3 we found a significant decrease in both groups and a steady level of T4- and T3-uptake without significant fluctuations. Thus it can be concluded that the effects of surgical trauma on plasma-TSH concentration are markedly similar to the effects of other anterior pituitary hormones, i.e. HGH, prolactin and ACTH.

Hypothalamic hypothyroidism with end-organ resistance--further personal observations

Further personal observations are made of the case of hypothalamic hypothyroidism with end organ resistance described in an earlier report. The course of the disorder on replacement therapy appears to be a relapsing one, with relapses provoked by seasonal changes and physical stresses. The relapses remit with increased doses of thyroid replacement. There is some evidence of increased levels of reverse T3 prior to T3 replacement and also evidence suggestive of a parallel hypothalamic hypoadrenal deficit.

A new prognostic index in surgery and parenteral feeding: the ratio of triiodothyronine to reverse triiodothyronine in serum (T3/rT3 ratio)

Serum concentrations of albumin, triiodothyronine (T3), and reverse triiodothyronine (rT3) were measured in 46 patients on the first day after routine gastrointestinal surgery, and the molar ratio T3/rT3 was calculated. The median value of this ratio, but not of albumin, was significantly lower in 11 who subsequently suffered major septic complications than in the remainder. Measurement of the ratio correctly predicted the outcome of 80% of individuals. The T3/rT3 ratio, midarm muscle circumference (MAMC), triceps skin fold (TSF) and serum concentrations of albumin and transferrin were measured in 23 patients at referral for parenteral feeding. Median values of T3/rT3 ratio, MAMC and transferrin, but not of the other parameters, were significantly lower in nine who died than in survivors. Measurements of the ratio, MAMC and transferrin correctly predicted the outcome of 87%, 78% and 74% of individuals, respectively.

Low T3 syndrome in patients following major surgery

Time sequence and specificity of thyroid hormones and biochemical parameters were investigated in patients following major surgery. Serum concentration of triiodothyronine decreases significantly following operation, with a biphasic regression. There is a reciprocal change in serum reverse triiodothyronine levels, but serum thyroxine levels show no significant change after operation. The significant decrease in serum concentration of alpha-2-macroglobulin and antithrombin III during and after surgery is the result of consumption of these inhibitors because the reciprocal change in serum concentration of elastase-like protease has been recognized. According to the change of curvilinear regression of serum triiodothyronine levels, 14 patients were grouped into 3. The patients for whom the curvilinear regression resembled a polynomial of degree 3 and 2 had a good prognosis, but the remaining 4 with no significant curvilinear regression had major complications and 2 died. It is meaningful that the postoperative change of triiodothyronine levels relates to the clinical outcome, to some degree.

Hyperthyroid heart disease

The importance of cardiovascular system involvement in hyperthyroidism has been recognized for many years. In the middle-aged and elderly patient, often with mild but prolonged elevation of plasma thyroid hormones, symptoms and signs of heart failure and complicating atrial fibrillation may dominate the clinical picture and mask the more classical endocrine manifestations of the disease. Pitfalls in diagnosis and the importance of early recognition and treatment are discussed. Despite experimental evidence for a short-term inotropic action of thyroid hormone excess, clinical data support the existence of a reversible cardiomyopathy in hyperthyroidism with impaired contractile reserve. Enhanced myocardial performance at rest primarily reflects the peripheral actions of thyroid hormone excess. Most, if not all, of the cardiac abnormalities return to normal once a euthyroid state has been achieved, although atrial fibrillation may persist in a minority. Optimum treatment requires rapid and definitive antithyroid therapy, usually using a large dose of radio-iodine, and rapid control of heart failure. Systemic anticoagulation is indicated in the presence of atrial fibrillation and should be continued until sinus rhythm has been present for at least three months, either spontaneously or after cardioversion.

A longitudinal evaluation of thyroid function in critically ill surgical patients

Thyroid hormone alterations (known as the "sick-euthyroid syndrome") are common following major surgery, but the time course for appearance and recovery from these alterations has not previously been longitudinally studied in a large group of surgical patients. The authors prospectively studied 59 patients undergoing major surgery (coronary artery bypass grafting, pneumonectomy, or subtotal colectomy). Compared with preoperative values, the mean serum T4, T3, free T3, and TSH concentrations decreased significantly (p less than 0.05) following surgery. Serum reverse T3 and T3 resin uptake index increased, while free T4 levels remained unchanged. These changes were seen within 6 hours of surgery and normalized by 1 week after surgery. Although the serum TSH response to TRH was normal before and after surgery in 56 of the 59 patients, the maximal TRH-induced increase in serum TSH and the integrated serum TSH response to TRH were suppressed in the early perioperative period. This postoperative TSH suppression correlated with elevated postoperative plasma dopamine concentrations (r = 0.57, p less than 0.05). Three patients with compensated primary hypothyroidism were detected in the study and represent the first documentation of serial thyroid hormone and TSH levels in hypothyroid patients undergoing major surgery. These patients had similar changes in thyroid hormone values compared with euthyroid patients. The serum TSH response to TRH was suppressed into the normal range in two of these patients on the day following surgery. The authors conclude that the sick-euthyroid syndrome occurs within a few hours of major surgery and remits with convalescence. Postoperative decreases in serum TSH may mask the diagnosis of hypothyroidism. Surgical consultants should be aware of these rapid postoperative changes so that thyroid function tests are properly interpreted in patients who have undergone major surgery.

The influence of povidone-iodine treatment on thyroid hormones in severe burns

Average iodine serum levels of 2.5 mg/100 ml were obtained in 10 patients with an average burn area of 50% and treated with povidone-iodine. Simultaneous measurements of the thyroid hormones failed to reveal any significant impairment of thyroid function apart from depressed T3 coupled with increased reverse T3. Similar findings were obtained with a control group of 10 multiply-injured patients. If renal function is unimpaired the resorbed iodine is quickly excreted. No clinical signs of iodine intoxication were observed.

[Post-traumatic hyperthyroxinemia or hyperthyroidism]

A fifteen year-old girl presented with several fractures after a road traffic accident. Five days later, fat embolism occurred, complicated by adult respiratory distress syndrome (ARDS) and disseminated coagulation (DIC). She was successfully managed in the intensive therapy unit, and was transferred to a general surgery after five weeks. Tachycardia and fever persisted without any other sign of infection. Clinical examination showed exophthalmos and a thyroid murmur. The venous concentration of T4 was increased: 204 nmol . 1(-1) (N: 70-150), whereas that of T3 was normal: 2.3 nmol . 1(-1) (N: 1-1.25). No other investigations were performed. The regression of clinical symptoms and a normalization of T4 were seen after treatment (carbimazole and acebutolol). Post-traumatic hyperthyroidism is discussed. Although classical, this syndrome was not well documented, as was shown in the literature survey. After trauma or an acute illness, an early fall in thyroid hormone concentrations was usually seen; a late increase in T4 was a rare occurrence.

The thyroid function in young men during prolonged exercise and the effect of energy and sleep deprivation

Thyroid function has been investigated in 24 young military cadets participating in a 5 d ranger training course with heavy physical exercise, calorie deficiency and deprivation of sleep. The cadets were divided into three groups, each differing in the amount of sleep and food consumption. The serum levels of thyroid hormones (T4, FT4, T3, rT3) and TBG showed a biphasic pattern during the course. Initially there was an increased secretion concomitant with an increased deiodination of T4 to T3 and rT3 mainly due to physical exercise. When the activities lasted for several days without sufficient food supply the thyroid secretion decreased simultaneously with an alteration of the peripheral conversion of T4 to rT3 instead of T3. A significant correlation was found between the changes in total and free thyroxine (r = 0.9) and between the increase in rT3 and decrease in T3 (r = 0.6). TSH decreased during the first day of activities and remained low throughout the course. The TSH response to TRH stimulation was greatly reduced during the course due to physical exercise and calorie deficiency. The present investigation demonstrates that the thyroid function is strongly affected by prolonged physical exercise and a negative energy balance, whereas sleep deprivation does not have any significant influence. The results indicate that the alteration observed is not regulated just by the hypothalamo-pituitary-thyroid-axis alone.

Hypothyroidism abolishes the hyperdynamic phase and increases susceptibility to sepsis

To evaluate the role of thyroid hormones in sepsis, 250-400 g rats were surgically thyroidectomized and 2-6 weeks later sepsis was produced by cecal ligation and puncture (CLP). In normal rats, total body O2 consumption (VO2) increased by 12.8% (P less than 0.05) in early sepsis (6 hr after CLP) and decreased slightly in late sepsis (16 hr after CLP). In hypothyroid (HT) rats, VO2 was depressed by 19.8% (P less than 0.05) in early sepsis and further decreased to 46.7% (P less than 0.001) of preoperative levels in late sepsis. Hepatic blood flow increased in early sepsis in normal rats but was unchanged in HT rats. The normal hyperglycemic response to early sepsis was also absent in HT rats. The respiratory control ratio (RCR) of isolated mitochondria with succinate was not increased in HT rats in early sepsis. In late sepsis, hypothyroid animals showed further decreases in VO2 and mitochondrial RCR, and, in contrast to normal rats, showed no change in blood glucose levels. Survival (5 days) following late sepsis in normal, HT, and HT rats given daily ip injections of thyroxine (30 micrograms/kg) were 65.2% (15/23), 30% (6/20) (P less than 0.025), and 77.1% (14/18), respectively. Thus, absence of thyroid hormone abolishes the hyperdynamic phase of sepsis and significantly increases mortality in sepsis, and thyroxine replacement following thyroidectomy prevents the increased mortality from sepsis.

Effect of the combination of dexamethasone and sodium ipodate on serum thyroid hormones in Graves' disease

To investigate the effect of the combination of dexamethasone (Dex) and sodium ipodate (SI) on hyperthyroidism, we studied 24 patients with typical Graves' disease, divided into four groups of six persons each. Three groups (Study I) were studied acutely (24 h) to determine the effects of Dex (5 mg every 12 h intramuscularly), SI (one oral dose of 3 g) and both drugs at the same doses, upon T4, T3, and rT3 at 0900 h before therapy was started and 24 h later. The group on Dex and that on SI had a similar T3 decrement of 25.9 +/- 4.0% and 35.8 +/- 5.0%, respectively, (P less than 0.05), whereas the effect of both drugs combined was greater (64.2 +/- 3.6%; P less than 0.01, Dex, and P less than 0.01, SI, respectively). The increment of rT3 was markedly greater in those patients on SI than in those on Dex (561.3 +/- 149.2% and 58.9 +/- 11%, respectively, P less than 0.025). A fourth group (Study II) was studied for seven days while receiving both Dex (1 mg orally three times per day) and SI (500 mg orally three times per day). Both T4 (from 18.8 +/- 1.1 to 13.1 +/- 1.1 micrograms/dl, P less than 0.02) and T3 (from 593 +/- 41 to 136.3 +/- 12.7 ng/dl, P less than 0.001) decreased at day 8. The initial brisk increment of rT3 at 24 h (808 +/- 149%, P less than 0.005) then diminished concomitantly with the fall of its precursor, T4.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone and thyroid function: clinical implications during antiarrhythmic therapy

Amiodarone, an iodinated benzofuran derivative, has electrophysiologic effects on cardiac muscle akin to those of hypothyroidism. It is possible that the drug exerts its salutary effect, at least in part, by selectively inhibiting the action of triiodothyronine (T3) on the myocardium. The drug produces complex changes in thyroid hormones, with significant elevations in thyroxine (T4) and reverse T3 (rT3), with minor decreases in T3, and with minor and transient increases in thyroid-stimulating hormone, but without effect on thyroid-binding globulin. These changes may interfere with the biochemical evaluation of thyroid function. Rarely, hypothyroidism or hyperthyroidism may develop during the course of amiodarone therapy, a complication caused by the iodine contained in the drug rather than by the direct pharmacologic actions of the compound. The incidence of altered thyroid function induced is likely to vary with populations susceptible to iodine-induced goiter. Under the action of amiodarone, serum rT3 levels increase as a function of dose and duration of therapy and therefore provide a basis for judging the magnitude of in vivo drug cumulation. It was found that therapeutic efficacy was usually predictable on the basis of the attainment of a defined range of serum values, established by a correlation of rT3 levels with therapeutic responses both during loading and maintenance phases as well as after withdrawal of treatment of steady-state drug effects. Serious adverse effects occurred nearly always in association with four- to fivefold increases of rT3 above baseline values, and disappeared when such levels fell as a result of dosage reduction or after temporary drug discontinuation. The data suggest that the determination of serum rT3 levels during amiodarone therapy provides a simple and reliable technique for monitoring the drug's antiarrhythmic efficacy and toxicity, thereby enhancing its clinical utility. The use of rT3 levels may permit the development of a safe but optimal therapeutic regimen for the control of a wide spectrum of refractory atrial and ventricular tachyarrhythmias. The use of this technique, however, presupposes the allowance that must be made for variations in the methods for the serum assay of rT3 and of the systemic conditions in which the rT3 levels fluctuate relative to severity of the illness.

Reverse T3 levels in affective disorders

Serum levels of 3,3',5' triidothyronine (reverse T3) were investigated in 32 patients with acute major depressive disorder. Twenty-six of these patients were also studied during a state of clinical improvement. Comparison subjects were 22 healthy controls, and 16 currently euthymic patients with histories of affective disorders (8 unipolar, 8 bipolar). The laboratory investigation included the determination of triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH), and thyroxin-binding globuline (TBG) levels in serum. The clinical symptoms were rated by the Comprehensive Psychopathological Rating Scale (CPRS) for depressive illness (CPRS global score), as well as the sum of 10 items (CPRS 10) and 22 items (CPRS 22) measuring depression. The patients were also divided into those having a normal or abnormal response to the dexamethasone suppression test; those having melancholia or not having melancholia; and those having primary or secondary depression. No significant difference in reverse T3 levels emerged among the patients with acute major depressive disorders, the euthymic unipolar or bipolar affective disorders, and the healthy controls. There were also no significant differences between those having an abnormal or normal DST test; those having primary or secondary depression; or those having melancholia or not having melancholia. In the group of patients with acute major depressive disorder, however, a significant increase in reverse T3 levels and a significant decrease in T3 levels, but no significant difference in T4 or TSH levels, were seen in the patients with the most pronounced clinical symptoms as measured by the CPRS. The implications of these findings are discussed.

Low serum 3,3',5-triiodothyronine (T3) and reciprocally high serum 3,3',5'-triiodothyronine (reverse T3) concentration in spinal cord injury patients

Thyroid function tests were performed on 115 spinal cord injury patients. Serum thyroxine, thyroid stimulating hormone, and T3 resin uptake were within normal range in all patients. Serum T3 levels tended to be low in paraplegic and quadriplegic patients, even though they were clinically euthyroid and other thyroid functions were normal. Serum reverse T3 levels were reciprocally higher in these patients.

Dose response of protein turnover in rat skeletal muscle to triiodothyronine treatment

Skeletal muscle protein turnover has been examined in thyroidectomized rats treated with 0, 0.3, 0.75, 2, 20 and 100 micrograms triidothyronine/day for 7 days by implanted osmotic minipump. Protein synthesis in gastrocnemius, plantaris and soleus muscle were measured in vivo by the constant infusion method and protein degradation estimated as the difference between gross and net rates of synthesis. Serum levels of triidothyronine (T3) and insulin were also measured in addition to oxygen consumption rates in some cases. Compared with untreated intact rats muscle growth rates were unchanged at 0.3, 0.75 and 2 micrograms T3/day and, judging by plasma T3 levels, 0.75 microgram T3/day was a replacement dose. Slowing of growth was evident in the untreated thyroidectomized rats mid-way through the 7 day experimental period (6-7 days after throidectomy). High doses of T3 (20 and 100 micrograms/day) promptly supressed growth but there was subsequent recovery. Protein synthesis and degradation were generally lower in the hypothyroid state and normal or elevated in the hyperthyroid state. The changes in protein synthesis were mediated by changes in both RNA concentration and RNA activity (protein synthesis per unit RNA). Gastrocnemius and plantaris muscles were most responsive in the hypothyroid range. Since protein synthesis is particularly depressed in these muscles in malnutrition, the fall in protein degradation induced by the lowered thyroid status in this condition will be an important adaptive response to conserve protein. The increased protein turnover in the hyperthyroid rats was most marked in the soleus muscle and it is argued that this is necessary to allow the changes in protein composition and metabolic character which occur in response to hyperthyroidism in this muscle.

[Changes in thyroid hormone levels following severe burns treated topically with povidone-iodine]

The serum concentrations of thyroxine (T4), triiodothyronine (T3) and TSH as well as the effective thyroxine ratio (ETR) and the resin-T3-uptake (RT3U) were studied in 23 severely burned patients during the whole time of hospitalisation. Topical treatment was carried out with povidone-iodine. In all patients T4 and T3 concentrations decreased significantly during the first two weeks especially in extensive burns. Lack of increase was a bad prognostic sign. ETR and RT3U underwent no remarkable changes. The TSH levels increased distinctively until the third week, decreased slowly and turned to normal values only in the late period of illness. The influence of iodine uptake due to external application is discussed.

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.

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.

Anterior pituitary, thyroid, parathyroid and adrenal responses to subtotal thyroidectomy in patients with Graves' disease

Changes in the serum levels of anterior pituitary, thyroid, parathyroid, and adrenal hormones following subtotal thyroidectomy in 31 patients with Graves' disease were investigated. In 14 patients, rapid ACTH tests were performed on the preoperative and the first, third, and seventh post-operative days. Remarkable differences were not seen with regard to the changes in anterior pituitary hormones or cortisol, compared to those seen during general surgery. As to the thyroid hormones, the serum level of triiodothyronine (T3) decreased markedly after surgery and fell to half that of the preoperative value on the first postoperative day. Thereafter, a low value of T3 was maintained during the early postoperative period. Unlike T3, the serum level of thyroxine (T4) decreased gradually until the 7th post-operative day. The levels of both epinephrine and norepinephrine increased transiently during surgery, but the serum level of norepinephrine increased again on the third postoperative day. In the postoperative period, almost half the number of patients showed an inadequate cortisol response to rapid ACTH tests. It is suggested that the unique responses, such as the rise in serum norepinephrine or an inadequate response of cortisol to ACTH, or hypocalcemia, after subtotal thyroidectomy in patients with Graves' disease is largely due to the rapid decrease of T3 in the hypothyroid state, as was noted during the postoperative period.

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.

Rapid adaptation of pituitary responsiveness to TRH in the post-surgical state. The role of free T3

In eight clinically and biochemically euthyroid patients undergoing routine major non-thyroidal surgery preoperative and daily postoperative serum concentrations of total and free thyroid hormones were measured. Thyrotrophin-releasing hormone (TRH) tests were performed preoperatively and on the first 3 postoperative days. There was a significant fall in mean serum total and free triiodothyronine (T3) concentrations on the postoperative days and mean reverse T3 concentrations rose reciprocally. There was no significant change in mean basal thyroid-stimulating hormone (TSH) values, but there was a significant increase in the mean TSH-response to TRH on the first postoperative day. The mean TSH response than declined sequentially until day 3 while mean free T3 concentrations remained significantly depressed. Mean serum free thyroxine(T4)concentrations remained normal during the study. Intrapituitary conversion of T4 to T3 or other down regulatory mechanisms could explain this rapid adaptation of the pituitary axis.

Circulating reverse triiodothyronine in humans during exercise

Circulating thyroxine (T4), triiodothyronine (T3) and reverse triiodothyronine (rT3) as well as blood lactate and glucose concentrations were measured in a group of 12 trained volunteer subjects prior to and after swimming 0.18 or 0.9 km, to determine if increase in metabolic activity was accompanied by diversion of T4 monodeiodination from the active (T4 to T3) to the inactive (T4 to rT3) pathway. The resting T4, T3, and rT3 levels were 8.5 micrograms . 100 ml-1, 108 ng . 100 ml-1, and 57 ng . 100 ml-1, respectively, whereas after 0.18 km of swimming the corresponding levels were 9.5 micrograms . 100 ml-1, 135 ng. 100 ml-1 and 70 ng . 100 ml-1. After 0.9 km of swimming, T4, T3, and rT3 levels were 9.0 micrograms . 100 ml-1, 126 ng . 100 ml-1, and 66 ng . 100 ml-1, respectively. The swimming was accompanied by hemoconcentration and increase in blood lactate but not in glucose concentrations. In two other investigations thyroid hormones were measured prior to and after 60 or 90 min of moderate exercise on a bicycle ergometer. This exercise had no effect on circulating thyroid hormone levels. Free thyroxine (FT4) concentration and thyroxine binding globulin (TBG) capacity were unaltered after exercise. In conclusion, brief strenuous swimming or moderate bicycle exercise had minor or no effect on thyroid hormone concentrations when consideration was given to the attendant hemoconcentration. Even when exercise induced small T3 and rT3 changes were noted, they were in the same direction (increase) thus demonstrating a lack of diversion of peripheral T4 monodeiodination.

Reduced active thyroid hormone levels after delivery

The effect of delivery on the serum concentration of thyroid hormones was studied in 25 euthyroid women. After delivery serum free and total T3 and T4 fell transiently with a simultaneous increase in reverse T3 while serum TSH and thyroxine binding globulin (TBG) concentrations showed no significant variation. These data suggest that i) similar to what happens in other stressful situations, delivery influences peripheral T4 metabolism, and ii) an elevation of TBG in serum in the early puerperium does not prevent these changes.