Changes In Serum Thyroid Hormones Research Articles

Are serum thyroid hormone changes in rats a reliable indicator for human neurodevelopmental effects? -Evaluation of different cases

Are serum thyroid hormone changes in rats a reliable indicator for human neurodevelopmental effects? -Evaluation of different cases

SAT-LB80 Elevated Pre-Op Thyrotropin Levels Are Associated With Increased 30-Day Mortality in Patients Undergoing Cardiac Surgery With Cardiopulmonary Bypass

BACKGROUND: The association between thyroid dysfunction and postoperative mortality is contentious. Thyroid function is frequently depressed during and after cardiopulmonary bypass surgical procedures, and this may adversely affect myocardial performance and postop outcome.OBJECTIVES: To study i) the changes and clinical significance of serum thyroid hormones during cardiopulmonary bypass (CPB), and ii) the association between biochemically assessed peri-op thyroid function and 30-day mortality after CBPSTUDY DESIGN: Prospective Cohort StudySUBJECTS: 279 patients undergoing various cardiac surgeries under cardiopulmonary bypass.METHODS: All consenting patients undergoing open heart surgery in last five years at a tertiary care centre in North-India were studied. The thyroid hormone levels (Total T3, T4 and TSH) were measured before admission, and postoperatively on Day 1 & 7, and 3 months following surgery. The patients’ gender, age, weight, body mass index, heart disease details, previous cardiac surgeries, and cardiac surgery-related data such as pump time, aortic clamping time, hypothermia duration, postoperative hemodynamic status and postoperative use of inotropic drugs were recorded and analysed. Patients were classified as having biochemically overt or subclinical hyperthyroidism or hypothyroidism, normal thyroid function, or non-classifiable state based on preoperative thyroid-stimulating hormone and total T4 values. Outcome data were collected from hospital records. Biochemical thyroid dysfunction was not systematically treated. Outcomes measured were length of ICU stay, postoperative complications and 30-day mortality.RESULTS: There was significant changes in thyroid function in patients undergoing cardiopulmonary bypass surgery (Fig 1). All patients showed a decrease in T3, T4 and TSH after surgery. Post-op complications were observed in 137 patients (49%) most common being atrial fibrillation (34%) followed by acute kidney injury (23%), infections (18%), dyselectrolytemia (7%), bleeding (1.4%) and ARDS (1.4%). Of 263 patients followed, eventually 26 patients expired with a mortality rate of 8.89% (95% CI, 0.4 - 19.4). Perioperatively, there was a significant correlation between 30-day with type of surgery (r, 0.26), aortic clamp time (r, 0.45), CBP time (r, 0.48), number of inotropes used (r, 0.57), hours of mechanical ventilation (r, 0.4), ICU stay (r, 0.13) and post-op complications (r, 0.24), as well as with the reduction in the thyroid hormone levels; 17 (7%), 3 (20%) and 6 (46%) patients of those with pre-op TSH level of <6.5, >6.5 and >10.5 mIU/L expired (p <0.001).CONCLUSION: Pre-op thyroid dysfunction is associated with increased mortality in patients undergoing cardiac surgery with CBP. Excess mortality with elevated serum TSH levels suggests the importance of timely detection and intervention in individuals with thyroid dysfunction undergoing cardiac surgery.Table of Contents oTable 1. Characteristics of patients who expired versus those who survived cardiac surgery with cardiopulmonary bypass (CPB) oFig 1. Changes in serum thyroid hormones during CPB surgery oTable 1. Characteristics of patients who expired versus those who survived cardiac surgery with cardiopulmonary bypass (CPB) oFigures in parenthesis indicate ±Standard Deviation, unless indicated otherwise oFig 1. Changes in serum thyroid hormones during CPB surgery

Evaluation of antithyroid potential of Luffa acutangula peel extract and its chemical constituents as identified by HR-LC/MS.

Although some reports are there indicating the medicinal values of fruit peels, on vegetable peels investigations are meager. The present study is an attempt to explore the hitherto unknown potential of Luffa acutangula peel extract in T4-induced hyperthyroid female mice. Animals were made hyperthyroid by administering pre-standardized dose of l-thyroxin (l-T4 at 0.5mg/kg/day) for 12 consecutive days and then the effects of the test peel extract at 25 and 50mg/kg for 15days were studied on the changes in serum thyroid hormones, glucose, different lipids; hepatic lipid peroxidation (LPO); enzymatic antioxidants such as superoxide dismutase, catalase, glutathione peroxidase, and in reduced glutathione. The main chemical constituents of the extract were identified by high resolution liquid chromatography mass spectrometry. Administration of the test peel extract to the hyperthyroid mice at both the test doses decreased the levels of serum thyroid hormones, glucose and tissue LPO suggesting its antithyroid, antihyperglycemic and antiperoxidative potential. These positive effects were also supported by an improved lipid profile as well as liver histology. LC-MS analyses revealed the presence of kaempferol-3-O-rutinoside, kameferol-O-neohesporoside, quercetin, cinnamic acid ethyl ester, caffeic acid derivatives such as 4-O-caffeyol quinic acid, 3-sinapoylquinic acid and 4,5-dihydroxyprenyl caffeate, orientin and sinapic acid. It is presumed that the antithyroid and anti-hyperglycemic actions of the test plant extract could be the result of antioxidative properties of these phytochemicals.

The Relationship Between Occupational Exposure to Low-dose Ionizing Radiation and Changes in Thyroid Hormones in Hospital Workers.

The effects of ionized radiation on the thyroid have been extensively studied. However, most studies have focused on high-dose radiation received accidentally or through therapy, and few were on low-dose occupational exposure. Using a retrospective cohort study design, we collected health examination reports from employees who worked on jobs with occupational exposure to radiation at a hospital to evaluate possible changes in the serum thyroid hormones and determine whether there is a dose-response effect. After excluding those with diseases that may affect thyroid function and who were pregnant at any given examination during the study periods we followed the remaining 326 workers for 12 years and evaluated the associations between radiation exposure and changes in serum thyroid hormones using the generalized estimating equation for repeated measures. Data from an external comparison cohort were used to adjust for changes over time. We observed declines in triiodothyronine (T3) and thyroxine (T4) over the study period, but not in thyroid-stimulating hormone (TSH). In addition, we found negative dose-response relationships between exposure duration and declines in the serum levels of T3 (a change of -0.037 ng/ml/year after adjusting for sex and age at the beginning of follow-up; 95% confidence interval [CI] = -0.042, -0.032 ng/ml/year) and T4 (-0.115 µg/dl/year; 95% CI = -0.140, -0.091 µg/dl/year). We also observed an increase in the TSH level (0.683 µIU/ml/year; 95% CI = 0.151, 1.214 µIU/ml/year) after the ninth year of follow-up. We concluded that despite low exposure doses, occupational exposure to ionizing radiation in healthcare workers still may be associated with the declines in the serum levels of T3 and T4.

Thyroid Functions and Trace Elements in Pediatric Patients with Exogenous Obesity

Obesity is a multifactorial disease developing following impairment of the energy balance. The endocrine system is known to be affected by the condition. Serum thyroid hormones and trace element levels have been shown to be affected in obese children. Changes in serum thyroid hormones may result from alterations occurring in serum trace element levels. The aim of this study was to evaluate whether or not changes in serum thyroid hormone levels in children with exogenous obesity are associated with changes in trace element levels. Eighty-five children diagnosed with exogenous obesity constituted the study group, and 24 age- and sex-matched healthy children made up the control group. Serum thyroid stimulating hormone (TSH), free thyroxine (fT4), free triiodothyronine (fT3), thyroglobulin (TG), selenium (Se), zinc (Zn), copper (Cu), and manganese (Mn) levels in the study group were measured before and at the third and sixth months of treatment, and once only in the control group. Pretreatment fT4 levels in the study group rose significantly by the sixth month (p = 0.006). Zn levels in the patient group were significantly low compared to the control group (p = 0.009). Mn and Se levels in the obese children before and at the third and sixth months of treatment were significantly higher than those of the control group (p = 0.001, p = 0.001). In conclusion, fT4, Zn, Cu, Mn, and Se levels are significantly affected in children diagnosed with exogenous obesity. The change in serum fT4 levels is not associated with changes in trace element concentrations.

Transient changes in thyroid functions tests after zoledronic acid infusion

Zoledronic acid (ZA) induces an acute phase response in association with elevation of serum cytokines, which possibly alter the 3 types of iodothyronine deiodinase activity. We therefore studied the possible alteration in thyroid function tests by ZA. We investigated the acute changes in serum thyroid hormones, TSH, cortisol, white blood cells, CRP, interleukin-6 (IL-6) and tumor necrosis factor (TNF-α), before (0) and 1, 2 and 3 days after iv infusion of 5 mg ZA in 24 asymptomatic postmenopausal women with osteoporosis (ZA group) in comparison with a placebo group. In the majority of patients the ZA infusion was associated with acute phase response and fever within 24h after infusion which became attenuated on day three. Concurrently with increase in serum cortisol, CRP, IL-6 and TNF-α, on day 1 and 2, total serum T3 (TT3), free T3 (fT3), total T4 (TT4) and fT4 decreased with a nadir on day 2 in association with an increase in the fT4/fT3 ratio and reverse T3 (rT3) levels. All thyroid function changes returned to the baseline levels on day 3, with cytokines still at higher levels, although lower than those on day 2. Serum TSH remained essentially unchanged throughout the study. The changes in thyroid hormones were at least in part explained by the increased TNF-α, but not by IL-6. ZA induces short term changes in thyroid hormones, characteristic of nonthyroidal illness syndrome (NTIS), in association with an increase in TNF-α and IL-6.

Evolution of Subclinical Hypothyroidism in Children Treated With Antiepileptic Drugs

The concentration levels of serum free thyroxine, serum free triiodothyronine, and thyroid-stimulating hormone were measured in 20 children receiving carbamazepine, 32 children receiving valproic acid, and 5 children receiving phenobarbital at the following times: (1) during chronic treatment, and (2) 3 months after the end of treatment with antiepileptic drugs. Patients during chronic treatment revealed significant changes in serum thyroid hormones, especially the children treated with carbamazepine and valproic acid. A number of children receiving long-term therapy with the two last antiepileptic drugs had varying grades of subclinical hypothyroidism. Three months after the end of treatment, a complete return to normal of all parameters was observed. These data demonstrate that the changes induced by these drugs are transient and reversible.

Prolactin, Cortisol Secretion and Thyroid Function in Patients with Stroke of Mild Severity

Different attempts were made to identify the variables that may be involved in the clinical course of cerebrovascular ischemia. In the case of stroke with mild severity (SMS), the clinical significance of neuroendocrine changes as well as of post-stroke depression (PSD) remains unknown. We therefore evaluated the presence of neuroendocrine changes in the acute and post-acute phase of SMS, and their potential role during convalescence. Serum cortisol, T4, T3, FT4, FT3, TSH and PRL levels were measured in 17 euthyroid patients with stroke on admission (day 1), following morning (day 2), 7 days and 3 months later. TSH and PRL secretion after TRH test were measured. Stroke severity on admission was determined by Scandinavian Stroke Scale (SSS). Montgomery-Asberg Depression Rating Scale (Madrs) was used for assessment of post-stroke depression. On admission, TSH and T3, were within normal limits and were greater compared to values on day 2. Lower basal TSH and decreased TSH response to TRH on day 2, were associated with stroke of greater severity. Delta-PRL after TRH on day 2 was higher in patients who develop PSD. Changes in serum thyroid hormones in SMS, reflects those of non-thyroidal illness. A mild stimulation of hypothalamic-pituitary-adrenal axis was detected. We provide evidence that PRL response to TRH, in the acute phase of stroke may be used as an index for early detection of PSD.

Serum concentration of soluble Fas in patients with autoimmune thyroid diseases.

Fas is an apoptosis-signaling receptor molecule found on the surface of a number of cell types. Malfunction of the Fas system accelerates autoimmune diseases, whereas its exacerbation may cause tissue destruction. Soluble Fas (sFas) molecule lacks the transmembrane domain due to alternative splicing and blocks Fas-mediated apoptosis. This study investigated serum levels of sFas in autoimmune thyroid diseases. Serum levels of sFas were determined by enzyme-linked immunosorbent assay in 46 patients with Graves' disease, 32 patients with Hashimoto's thyroiditis, 14 patients with silent thyroiditis, and 24 normal controls. Compared with normal subjects (1.43+/-0.37 ng/mL), sFas was increased in thyrotoxic patients with Graves' disease (1.89+/-0.47 ng/mL, p < 0.001), and was decreased in patients with Graves' disease in remission (1.02+/-0.41 ng/mL, p < 0.001) and in euthyroid patients with Hashimoto's thyroiditis (0.97+/-0.25 ng/mL, p < 0.0001), but was normal in hypothyroid patients with Hashimoto's thyroiditis and in thyrotoxic patients with silent thyroiditis. Thus, changes in serum levels of sFas could not be explained by changes in serum thyroid hormones, although sFas concentration correlated with free thyroxine (r = 0.692, p < 0.0001). Also, the levels of sFas significantly correlated with the activities of TSH receptor antibody in Graves' disease (r = 0.671, p < 0.0001). Increased sFas in Graves' disease suggests increased expression of alternatively spliced Fas mRNA variant that produces sFas protein and decreased of cell surface expression of Fas, and may induce thyroid cell growth and production of TSH receptor antibody by protecting against apoptosis of thyroid cells and autoreactive B cells. Decreased sFas in Hashimoto's thyroiditis suggests decreased Fas mRNA variant and increased full-length Fas mRNA and membrane Fas, and may induce destruction of thyroid cells by promoting apoptosis of thyroid cells.

Acute administration of T3 or rT3 failed to improve outcome following resuscitation from cardiac arrest in dogs

Documentation of profound changes in serum thyroid hormone concentrations associated with cardiac arrest and resuscitation, as well as other acute emergencies, have spurred evaluation of possible therapeutic thyroid hormone administration. Acute and significant, this state, characterized by abnormally low serum thyroid hormone concentrations, may indicate selective thyroid replacement therapy. In a previous investigation, post-resuscitation infusion of levothyroxine sodium (L-T4) to normalize serum 3,5,3′-triiodothyronine (T3) concentrations was associated with significant reduction of neurologic deficit caused by severe global cerebral ischemia. Since L-T4 has been reported to act directly or via one of its metabolites, most likely T3, this most active form of thyroid hormone was tested. When L-T4 reduced the neurologic deficit, an increase in 3,3′,5′-triiodothyronine (rT3) was also observed. This study therefore determined whether a post-resuscitation treatment with either T3 ( n = 8) or rT3 ( n = 8) provided protection against global cerebral ischemia comparable to that of L-T4. Global cerebral ischemia was achieved with 9 min of ventricular fibrillation. Following resuscitation, one of three solutions (saline group as a control) was infused for 24 h at rates that reproduced the normal serum T3 concentrations or the rT3 concentrations achieved previously during the L-T4 therapy. The successful elevation of T3 and mimicking rT3 concentrations was assessed and confirmed by radioimmunoassay (RIA). In addition, TSH levels were measured by a novel RIA specific for canine thyroid-stimulating hormone (cTSH). Neurologic deficit was assessed with a well-standardized neurologic deficit examination. In contrast to previous studies using L-T4 infusion, no significant reduction of neurologic deficit was observed. Serum thyroid hormone changes confirmed previously described decreases and in no case did changes in cTSH appear causal in these changes. Thus, we concluded that L-T4 may offer a therapeutic advantage over T3 or rT3.

Long-term observation of serum thyroglobulin after resection of nontoxic goiter and relation to ultrasonographically demonstrated relapse.

The object was to carry out a prospective study of the changes in serum thyroid hormones and thyroglobulin (Tg) following resection of nontoxic goiter and to investigate if there was a correlation to the pattern of relapse. A group of 39 consecutive patients, mainly with nodular, nontoxic goiter, were studied for 13 years following thyroidectomy. No thyroid hormone replacement therapy was given after surgery. The preoperative serum Tg level was elevated. After operation the mean serum Tg declined to a nadir of 43 micrograms/L at 1 year and subsequently increased to 90 micrograms/L at 10 years, with large individual differences. In 19 patients the serum Tg increased, in 1 it decreased, and in 19 no significant alteration was observed. Serum free thyroxine and triiodothyronine indices decreased following resection but achieved normal levels within 6 to 12 months. Serum thyroid-stimulating hormone increased after resection, with a peak level 1 month after surgery, but it returned to normal levels at 1 year and remained stable for the rest of the period. At 13 years after resection the thyroid volume was determined by ultrasonography in 30 of the patients. In 10 patients the thyroid volume was enlarged (>/= 28 ml). In this group a rise of average serum Tg after resection [DeltaTg(10-1 year)] of 133 micrograms/L was observed, compared to 26 micrograms/L in the 20 patients without sonographic relapse (volume < 28 ml). A positive correlation was demonstrated between serum DeltaTg(10-1 year) postsurgically and thyroid volume 13 years after surgery. However, an overlap was observed between the groups with and without ultrasonographic relapse, probably in part due to large differences in the Tg synthesis activity of different follicle cell clones. It is concluded that repeated serum Tg determinations may provide biochemical evidence of increased growth activity of thyroid remnants monitored after goiter resection.

Central hypothyroidism resulting from pituitary suppression and peripheral thyrotoxicosis in a premature infant born to a mother with Graves disease

We observed the sequential changes in serum thyroid hormones and thyroid-stimulating hormone receptor antibodies in an infant born at 30 weeks of gestation to a mother with florid Graves disease. Transient central hypothyroidism caused by pituitary suppression was observed after the resolution of peripheral thyrotoxicosis induced by thyroid-stimulating antibody. Central hypothyroidism became overt when the suppression of the pituitary gland after fetal thyrotoxicosis was combined with weak activity of thyroid-stimulating antibody after birth. (J P EDIATR 1995;127:809-11)

Endocrine and cytokine changes during elective surgery.

Elective surgery was used as a model of severe non-thyroidal illness (SNTI) to study the inter-relation between changes in serum thyroid hormones, thyroid stimulating hormone (TSH), cortisol, and interleukin 6 concentrations. The study was designed to determine whether the expected interleukin 6 increases after surgery are the cause of decreased serum tri-iodothyronine (T3) concentration normally observed following severe trauma. Blood was sampled for 24 hours before, during, and for 48 hours after abdominal surgery under general anaesthesia in 11 patients. Total T3 decreased 30 minutes after induction and continued to decrease at 24 hours. After a transient increase at 30 minutes, free T3 also decreased, and free thyroxine (T4) concentrations, other than a similar transient increase, did not change. TSH concentrations were increased at four hours and the nocturnal surge was suppressed. The increase in the serum interleukin 6 concentration was not observed until four hours. Cortisol concentrations were increased at 30 minutes and peaked at four hours. Therefore, the early changes in thyroid hormones and TSH accompanying surgery do not seem to be caused by changes in interleukin 6 concentrations.

Serum thyroid hormone, guanine and protein profiles during smoltification and after thyroxine treatment in the masu salmon, Oncorhynchus masou

Changes in serum thyroid hormones (thyroxine:T 4, triiodothyronine:T 3), skin and serum guanine, total serum protein and albumin-like protein (α 1-protein) concentrations were investigated during smoltification in yearling masu salmon, Oncorhynchus masou. Moreover, the effects of T 4 on their concentrations were examined in the underyearling fish. Skin and serum guanine levels increased as smoltification progressed. T 4 and T 5 levels followed skin and serum guanine profiles. At least four guanine-binding proteins were found in the serum. One of them was identified immunologically as a 1-protein. T 4 treatment caused increase in guanine levels in skin and serum. However, T 4 led to no change of a 1-protein concentrations. The present results suggest a possible pathway whereby guanine is induced by T 4 and transported to the skin by guanine-binding protein in the blood.

Relationship between inhibitor of extrathyroidal 5'-deiodinase activity and serum free fatty acid in children with nonthyroidal illness and acute ketosis.

To clarify whether serum free fatty acid (FFA) is an inhibitor of extrathyroidal conversion (IEC) of thyroxine (T4) to thyronine (T3), we measured the concentration of FFA, IEC activity and thyroid hormones in normal subjects, acute ketotic children and children with low T3 syndrome due to nonthyroidal illness (NTI). Iodothyronine (I) 5'-deiodinase activity was assayed with reverse triiodothyronine (rT3) as substrate and liberated 125I-was measured. The IEC was determined by the inhibition of I 5'-deiodination by ether extract of sera or standard oleate solution. IEC values were represented as mM oleate. The serum concentration of FFA was 0.470 +/- 0.117 (SD) mM in 11 normal subjects, and it was significantly higher (1.242 +/- 0.248 mM; P < 0.01) in 10 acute ketotic children and in 7 samples from 6 NTI children (0.904 +/- 0.530 mM; P < 0.05). In contrast, there was no difference in IEC among three groups (normal subject, 0.451 +/- 0.069 mM; acute ketosis, 0.437 +/- 0.040 mM; NTI, 0.465 +/- 0.224 mM). No correlations were found between IEC activity and the serum FFA concentration or thyroid hormones in 28 samples from three groups. The sequential changes in serum thyroid hormones, FFA and IEC in 3 of 6 NTI children revealed no consistent relationship. Furthermore, one NTI child had significantly high IEC (> 1.000 mM) but its serum FFA (1.182 mM) was below the mean value for the acute ketotic group. These results indicate that 1) many NTI patients may bear no relation to IEC and 2) IEC may not be caused by serum FFA only but includes several factors.

Serum thyroid hormone changes in head and neck cancer patients treated with microwave hyperthermia on lymph node metastasis

Eleven patients with head and neck cancer (ten men, one woman; mean age, 65 years) (larynx, six; oropharynx, two; tongue, one; skin, one; thyroid, one) with regional lymph node enlargements either in contiguity or firmly adherent to the vascular structures of the neck have been treated by means of external microwaves (915, 434 MHz) applicators. All patients were treated by hyperthermia (42-45 degrees C) alone (ten sessions, twice a week, each lasting 30 minutes). Thyroid hormones (T4, T3, FT4, FT3, rT3, thyroid stimulating hormone less than obTSH]) were evaluated during sessions 1, 2, 3, and 8, just before the session (time [t] = 0) and at 10-minute intervals during the heating (t = 10, t = 20, t = 30). Blood was also taken 10 (t = 40) and 30 minutes (t = 60) after the end of each session. T4 showed a decreasing trend; T3 decreased significantly from t = 10 and reached the lowest values at t = 40 and t = 60; FT4 decreased at t = 40 and t = 60 at all sessions; FT3 and rT3 showed no change; TSH decreased at t = 10 until t = 40.

Melatonin specifically stimulates type-II thyroxine 5'-deiodination in brown adipose tissue of Syrian hamsters.

The response of type-II thyroxine 5'-deiodinase (5'-DII) to melatonin treatment was studied in the Syrian hamster. Male hamsters were treated for 15 days with a s.c. pellet containing melatonin, and 5'-DII activity in brown adipose tissue, anterior pituitary gland, Harderian gland and pineal gland was measured using a radioenzymatic technique. Melatonin-treated animals exhibited enhanced 5'-DII activity restricted to brown adipose tissue; the increase was threefold above the values measured in the control group. Serum concentrations of thyroid hormones were unaffected by melatonin treatment. We conclude that the stimulatory effect of melatonin on type-II thyroxine 5'-deiodination is specifically directed to the isoenzyme located in brown adipose tissue and is not accompanied by changes in serum thyroid hormones.

Sensitivity changes to inotropic agents in rabbit atria after chronic experimental diabetes.

The effect of experimental diabetes on the sensitivity of isolated left atrial strips to inotropic agents was investigated in rabbits made diabetic with alloxan. After 4 weeks of diabetes no change in sensitivity was detected in response to isoproterenol or ouabain. In contrast, 15 weeks of diabetes induced a decreased sensitivity to beta-adrenergic stimulation, exhibited as a shift to the right in concentration-response curves obtained in response to isoproterenol and noradrenaline. In addition, after 15 weeks of diabetes the inotropic response to ouabain was depressed, and a small decrease in sensitivity was detected in response to forskolin. In contrast, no significant changes in the concentration-response curves obtained from alpha-adrenergic stimulation by phenylephrine or calcium chloride were detected. Unlike the streptozotocin diabetic rat, which exhibits low serum thyroid hormone levels, no changes in serum thyroid hormones were detected in the alloxan diabetic rabbit. It is suggested that the increased inotropic sensitivity to alpha-adrenergic agonists observed in the diabetic rat, but not in the rabbit, may be due to low serum thyroid hormone levels. In contrast, the deleterious effects of diabetes on beta-adrenergic and ouabain sensitivity occur independently of changes in serum thyroid hormones.

Free and Total Thyroid Hormones in Serum of Holstein Cows

Basic parameters are reported for free thyroxine and triiodothyronine in blood serum of dairy cattle. Free thyroxine ranged from a low of 1.47 ng/dl in the summer to 1.86 ng/dl in the spring and from 1.37 ng/dl in early lactation to 1.85 ng/dl in midlactation. The average free triiodothyronine went from a low of 2.98 pg/ml in winter to a high of 6.23 pg/ml in the fall and from 3.45 pg/ml in early lactation to 5.37 pg/ml in midlactation. The free fraction of the serum compared with the total fraction averaged .0267% for thyroxine and .291% for triiodothyronine. Free and total thyroxine were high in fall, low in winter, and intermediate in spring and summer. Free and total triiodothyronine showed a similar pattern with a greater magnitude in the variations. Even though the thyroid hormone secretion rate was higher in winter (earlier studies), increased tissue utilization kept serum concentrations low. Free and total thyroxine and triiodothyronine were low in early lactation due to high demands from peak milk production. Stage of lactation had a much greater influence on changes in serum thyroid hormones than did season.

Endocrine effects of repeated sauna bathing.

Ten healthy male and seven female volunteers were exposed to dry heat (in a Finnish sauna 80 degrees C) 1 h twice a day for 7 days. The levels of ACTH in plasma, cortisol, TSH, thyroid hormones, testosterone, gonadotropins, prolactin and GH in serum and urinary excretion of catecholamines were determined before the experiment, and on the first, third and seventh days. Females participated only in prolactin studies. During the experiments there were no statistically significant changes in serum thyroid hormones, TSH, testosterone, FSH and LH levels. Serum cortisol and plasma ACTH decreased and urinary catecholamine increased slightly at the end of the experiment (P less than 0.05). Serum GH and prolactin in males exhibited 16- and 2.3-fold increases (P less than 0.01), respectively. In females serum prolactin rose over four-fold (P less than 0.01). The GH rise in response to hyperthermia declined after the third day but prolactin remained elevated at the end of the experiments in males. The release of prolactin in females was also high and may be associated with the transient amenorrhoea that occurred in five out of seven subjects after the experiment. The increased release of prolactin and perhaps that of GH may be associated to the heat-exposure-induced dehydration.