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Thyroid Hormone Concentrations (thyroid + hormone_concentration)
Selected AbstractsPlasma Thyroid Hormone Concentrations in Dogs Competing in a Long-Distance Sled Dog RaceJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 4 2003David L. Panciera Plasma thyroxine (T4), 3,5,3,-triiodothyronine (T3), total protein, and albumin concentrations were measured in 15 dogs both before and after completion, and in an additional 16 dogs before and 24 dogs after completion, of a long-distance sled dog race. The plasma T4 concentration (mean ± SD) decreased significantly from 18.2 ± 5.4 nmol/L before to 14.3 ± 3.5 nmol/L after the race in dogs evaluated at both times and decreased significantly from 21.8 ± 10.5 nmol/L before to 15.8 ± 4.9 nmol/L after the race in dogs sampled only before or only after the race. The mean plasma T3 concentrations in dogs measured twice decreased significantly from 1.20 ± 0.48 nmol/L before to 0.74 ± 0.42 nmol/L after the race, as well as in dogs measured either before (1.28 ± 0.36 nmol/L) or after (0.69 ± 0.28 nmol/L) the race, respectively. Plasma total protein and albumin concentrations decreased significantly after completion of the race. No significant change was noted in 4 control dogs that did not compete in the race and were tested during a similar time period. The plasma concentrations of T4 and T3 were lower than the normal reference range established for this laboratory in 23 and 39%, respectively, of Alaskan sled dogs tested before the race. Plasma thyroid hormone concentrations frequently are below normal in conditioned Alaskan sled dogs and are further reduced after prolonged submaximal exercise. [source] TSH concentration within the normal range is associated with cognitive function and ADHD symptoms in healthy preschoolersCLINICAL ENDOCRINOLOGY, Issue 6 2007Mar Įlvarez-Pedrerol Summary Objective, Thyroid hormone concentrations outside the normal range affect brain development, but their specific influence on behaviour and mental abilities within normal values is unknown. The objective of this study was to investigate whether thyroid hormone concentrations are related to neurodevelopment and ADHD (attention deficit and hyperactivity disorder) symptoms in healthy preschoolers. Design subjects and measurements, Children from two general population birth cohorts in Menorca (n = 289) and Ribera d'Ebre (n = 53), Spain, were assessed in a cross-sectional study at the age of 4. Thyroid hormones (free T4 and T3) and TSH concentrations were measured and mental and motor development was assessed using McCarthy's scales for neuropsychological outcomes and ADHD-DSM-IV for attention deficit and hyperactivity/impulsivity symptoms. Results, Children with TSH concentrations in the upper quartile of the normal range performed lower on McCarthy's scales and were at higher risk for attention deficit and hyperactivity/impulsivity symptoms. In the Menorca cohort, a decrease of 5·8 (P < 0·05) and 6·9 (P < 0·01) points was observed in memory and quantitative skills, respectively. In contrast, high T4 concentrations were associated with decreased risk of having 1,5 attention deficit symptoms (odds ratio: 0·25; P < 0·01); these findings were observed in both cohorts despite differences in mean TSH concentrations. No associations were observed with T3. Conclusions, Despite being within the normal range, high TSH concentrations are associated with a lower cognitive function and high TSH and low free T4 with ADHD symptoms in healthy preschoolers. Statistically significant differences were observed in the highest quartiles of TSH, suggesting a need for re-evaluation of the upper limit of the normal TSH range. [source] Maternal thyroid hormone concentration during late gestation is associated with foetal position at birthCLINICAL ENDOCRINOLOGY, Issue 5 2009Hennie A. Wijnen Summary Objective, To evaluate whether there is an association between maternal thyroid hormone and foetal cephalic head position at term gestation. Context, Rotation and flexion of the head enables the foetus to negotiate the birth canal. Low-normal range thyroid hormone concentrations in euthyroid pregnant women constitute a risk of infant motor abnormality. We hypothesized that low normal maternal thyroid hormone levels are associated with increased risk of abnormal foetal position at delivery. Design, In 960 healthy Dutch women with term gestation and cephalic foetal presentation, thyroid parameters [foetal T4 (FT4), TSH and thyroid peroxidase antibody] were assessed at 36 weeks of gestation, and related to foetal head position (anterior cephalic vs. abnormal cephalic) and delivery mode (spontaneous vs. assisted delivery). Results, Women presenting in anterior position (n = 891) had significantly higher FT4 levels at 36 weeks of gestation than those with abnormal cephalic presentation (n = 69). There were no between-group differences for TSH. Regression analyses indicated that the risk of abnormal head position decreased as a function of increasing FT4 [single odds ratio (OR) = 0·87, 95% confidence intervals (CI) 0·77,0·98; multivariate OR = 0·88, 95% CI 0·72,0·99)]. A similar inverse relationship between maternal FT4 and risk of assisted delivery was obtained (OR = 0·86, 95% CI 0·79,0·95; OR = 0·91, 95% CI 0·84,0·98). Conclusion, The lower the maternal FT4 concentration at 36 weeks of gestation, the higher the risk of abnormal cephalic foetal presentation and assisted delivery. [source] The quantity of thyroid hormone in human milk is too low to influence plasma thyroid hormone levels in the very preterm infantCLINICAL ENDOCRINOLOGY, Issue 5 2002Aleid G. Van Wassenaer Summary background Thyroid hormone is crucial for brain development during foetal and neonatal life. In very preterm infants, transient low levels of plasma T4 and T3 are commonly found, a phenomenon referred to as transient hypothyroxinaemia of prematurity. We investigated whether breast milk is a substantial resource of thyroid hormone for very preterm neonates and can alleviate transient hypothyroxinaemia. Both the influence of breast feeding on plasma thyroid hormone levels and the thyroid hormone concentration in preterm human milk were studied. methods Two groups were formed from the placebo group of a randomized thyroxine supplementation trial in infants born at < 30 weeks' gestational age on the basis of the mean breast milk intake during the third, fourth and fifth weeks of life. One group received more than 50% breast milk (mean breast milk intake 84%, n = 32) and the other group less than 25% breast milk (mean breast milk intake 3·3%, n = 25). Plasma thyroid hormone concentrations were compared between the two groups. Breast milk was collected from mothers of infants participating in the same trial and the thyroxine concentration in breast milk was measured with RIA after extraction. results No significant differences were found between both groups in plasma concentrations of T4, free T4, T3, TSH, rT3 and thyroxine-binding globulin (TBG), which were measured once a week. Thyroxine concentration in breast milk ranged between 0·17 µg/l and 1·83 µg/l (mean 0·83, SD 0·3 µg/l) resulting in a maximum T4 supply of 0·3 µg/kg via ingested breast milk. In formula milk, the T4 concentration was equally low. Protease treatment did not influence the measured T4 concentrations. conclusions No differences in plasma thyroid hormone between breast milk-fed and formula-fed infants were found. The amount of T4 present in human milk and formula milk is too low to alter the hypothyroxinaemic state of preterm infants. [source] Pituitary and autonomic responses to cold exposures in manACTA PHYSIOLOGICA, Issue 4 2005J. Leppäluoto Abstract This review presents hormonal responses to various cold exposures and their calorigenic effects in man and some animals. Previous studies in rats have shown that cold exposures activate the hypothalamic-pituitary-thyroid axis. Increased thyroid hormone concentrations lead to heat production via general stimulation of metabolism (obligatory thermogenesis) and possibly via activation of thyroid hormone receptors and uncoupling protein 1 (UCP 1) and deiodinase enzyme genes in the brown adipose tissue (BAT). In human subjects long-term cold exposures do not seem to activate the pituitary-thyroid axis, but rather accelerate the elimination of triiodothyronine (T3), leading to low serum concentrations of free T3 hormone. In corollary to this a hypothyreotic condition with increased serum thyroid-stimulating hormone and impaired mood and cognitive performance can be observed after long-term cold exposures such as wintering. During cold exposures the sympathetic nerve system is activated and noradrenaline is released to blood circulation and to BAT, where it leads to production of cAMP, lipolysis and free fatty acids. Free fatty acids open the mitochondrial proton channel protein in BAT. Protons enter the mitochondria and inhibit ATP synthesis (uncoupling). By this way energy is transformed into heat (facultatory or adaptive thermogenesis). In adult human subjects the amount of BAT is small and adaptive thermogenesis (non-shivering thermogenesis) has a smaller role. UCP 1 with other uncoupling proteins may have other functions in the control of body weight, sugar balance and formation of reactive oxygen species. [source] Effects of pre- and postnatal polychlorinated biphenyl exposure on metabolic rate and thyroid hormones of white-footed mice,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2001John B. French Jr. Abstract Energy budgets have proven to be a valuable tool for predicting life history from physiological data in terrestrial vertebrates, yet these concepts have not been applied to the physiological effects of contaminants. Contaminants might affect energy budgets by imposing an additional metabolic cost or by reducing the overall amount of energy taken in; either process will reduce the energy available for production (i.e., growth or reproduction). This study examined whole animal energetic effects of polychlorinated biphenyl (PCB) exposure in white-footed mice (Peromyscus leucopus). Exposure to PCBs is known to reduce concentrations of plasma thyroid hormones, and thyroid hormones exert strong control over the rate of energy metabolism in mammals. Peromyscus leucopus that were proven breeders were fed PCBs in their food at 0, 10, and 25 ppm. Through lactation, offspring were exposed to PCB from conception and were maintained on the maternal diet to adulthood. No effects were seen on energy metabolism (O2 consumption, measured in adulthood) or on growth, but there were large dose-dependent decreases in thyroid hormone concentrations, particularly T4. The apparent disparity in our data between unchanged metabolic rates and 50% reductions in T4 concentrations can be rationalized by noting that free T3 (the fraction not bound to plasma protein) in treated mice was not significantly different from controls and that metabolism is most strongly influenced by free T3. Overall, this study did not demonstrate any energetic consequences of PCB exposure in P. leucopus at dietary concentrations up to 25 ppm. [source] Effects of fungicides on thyroid function, metabolism, and thermoregulation in cotton rats,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2001Thomas E. Tomasi Abstract Among the myriad of recent studies on endocrine-disrupting chemicals, relatively few involve thyroid disruption, and most of these address exposure/disruption during embryonic life. Of those involving adult vertebrates, the endpoints examined are thyroid measurements. Even though thyroid disruption could potentially interfere with energy metabolism and thermoregulation such that over-winter survival might be compromised, the possible energetic consequences of these thyroid perturbations have not been investigated. We assessed thyroid function and measured resting metabolic rates of cotton rats chronically exposed to the fungicides vinclozolin or mancozeb. In addition, we measured norepinephrine-induced nonshivering thermogenesis and cold-induced thermogenesis and then cold-acclimated the mancozeb animals. Although thyroid hormone concentrations generally decreased, this was compensated for by an increase in thyroxine turnover (vinclozolin study only) such that thyroxine utilization rate was not different. In addition, there was no difference between the treated and control animals in any of the metabolic parameters measured. It is concluded that wild rodents exposed to these compounds are not energetically compromised. [source] Thyroid Function in Girls with Epilepsy with Carbamazepine, Oxcarbazepine, or Valproate Monotherapy and after Withdrawal of MedicationEPILEPSIA, Issue 3 2004Leena K. Vainionpää Summary: Purpose: Antiepileptic drugs may affect the serum thyroid hormone concentrations. The aim of this study was to evaluate thyroid function in 78 girls taking carbamazepine (CBZ), oxcarbazepine (OXC), or valproate (VPA) monotherapy for epilepsy and after withdrawal of the treatment. Methods: Forty-one girls taking VPA, 19 taking CBZ, and 18 taking OXC for epilepsy, as well as 54 healthy age-matched controls, aged 8 to 18 years, participated in the study. All the girls were examined clinically, and their pubertal stage was assessed. Blood samples were obtained for thyroid hormone and antibody assays. These examinations were repeated after a mean follow-up of 5.8 years to assess thyroid function, and 64 (82%) of 78 patients and 42 (78%) of 54 controls agreed to participate in the second evaluation. Results: In the first evaluation, the mean serum thyroid hormone concentrations were lower in the girls taking CBZ [thyroxine (T4), 70.2; SD, 10.9 nM; and free thyroxine (FT4), 11.5; SD, 1.8 pM] or OXC (T4, 74.9; SD, 16.4 nM; and FT4, 11.3; SD, 1.8 pM) than in the control girls (T4, 96.6; SD, 15.1 nM, and FT4, 14.4; SD, 1.5 pM; p < 0.001, all comparisons). However, thyrotropin (TSH) concentrations were normal in the girls taking CBZ or OXC. Sixty-three% of the girls taking CBZ and 67% of the girls taking OXC had serum T4 and/or FT4 levels below the lower limit of the reference range. The VPA-treated girls with epilepsy had normal serum T4 and FT4 concentrations, but slightly increased TSH levels (3.3; SD, 1.5 mU/L; p < 0.01) compared with the control girls (2.5; SD, 1.0 mU/L). Normal serum hormone concentrations were restored in the patients who discontinued the medication. Conclusions: Both CBZ and OXC reduce serum thyroid hormone concentrations in girls with epilepsy. Conversely, VPA is associated with normal serum thyroid hormone and increased thyrotropin levels. However, our results suggest that the changes in serum thyroid hormone and thyrotropin levels are reversible after withdrawal of the medication. [source] Thyroid hormone responses to endurance exerciseEQUINE VETERINARY JOURNAL, Issue S36 2006E. A. GRAVES Summary Reasons for performing study: Limited information exists about changes in circulating thyroid hormone concentrations during prolonged endurance exercise in horses. Objective: To examine the effects of prolonged exercise on serum iodothyronine concentrations in horses performing endurance exercise of varying distances. Methods: Serum concentrations of iodothyronines were measured in horses before and after completion of 40, 56, 80 and 160 km endurance rides (Study 1); daily during a 5 day, 424 km endurance ride (Study 2); and before and for 72 h after completion of a treadmill exercise test simulating a 60 km endurance ride (Study 3). Results: In Study 1, 40 and 56 km of endurance exercise had little effect on serum iodothyronine concentrations with the exception of a 10% decrease (P<0.05) in free thyroxine (FT4) concentration after the 56 km ride. In contrast, total thyroxine (T4), total triiodothyronine (T3), FT4 and free triiodothyronine (FT3) concentrations all decreased (P<0.05) after successful completion of 80 and 160 km rides, with decreases ranging from 13,31% and 47,54% for distances of 80 and 160 km, respectively. Further, pre-ride T4 concentration was lower (P<0.05) and FT3 concentration was higher (P<0.05) in horses competing 160 km as compared to horses competing over shorter distances. In Study 2, serum concentrations of T4, T3 and reverse triiodothyronine (rT3) progressively decreased (P<0.05) over the course of the multi-day ride. In Study 3, the greatest decrease (P<0.05) in all iodothyronines was observed at 12 h of recovery, ranging from 25% for FT4 to 53% for FT3, but all thyroid hormone concentrations had returned to the pre-exercise values by 24 h of recovery. Conclusion: Endurance exercise results in transient decreases in serum iodothyronine concentrations. Potential relevance: These data are important to consider when thyroid gland function is assessed by measurement of serum iodothyronine concentrations in endurance horses. [source] Regulation of post-larval development in the European eel: thyroid hormone level, progress of pigmentation and changes in behaviourJOURNAL OF FISH BIOLOGY, Issue 1 2003I. M. Jegstrup Based on thyroid hormone concentrations and histological criteria, glass eels of Anguilla anguilla caught in the French Atlantic coast in January and November were found to be late metamorphic. The pigmentation of the glass eels was demonstrated to be regulated by thyroid hormones, and evidence is given that together, the end of the progression of pigmentation, a fully developed gut and a change in behaviour marked the end of metamorphosis. [source] Plasma Thyroid Hormone Concentrations in Dogs Competing in a Long-Distance Sled Dog RaceJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 4 2003David L. Panciera Plasma thyroxine (T4), 3,5,3,-triiodothyronine (T3), total protein, and albumin concentrations were measured in 15 dogs both before and after completion, and in an additional 16 dogs before and 24 dogs after completion, of a long-distance sled dog race. The plasma T4 concentration (mean ± SD) decreased significantly from 18.2 ± 5.4 nmol/L before to 14.3 ± 3.5 nmol/L after the race in dogs evaluated at both times and decreased significantly from 21.8 ± 10.5 nmol/L before to 15.8 ± 4.9 nmol/L after the race in dogs sampled only before or only after the race. The mean plasma T3 concentrations in dogs measured twice decreased significantly from 1.20 ± 0.48 nmol/L before to 0.74 ± 0.42 nmol/L after the race, as well as in dogs measured either before (1.28 ± 0.36 nmol/L) or after (0.69 ± 0.28 nmol/L) the race, respectively. Plasma total protein and albumin concentrations decreased significantly after completion of the race. No significant change was noted in 4 control dogs that did not compete in the race and were tested during a similar time period. The plasma concentrations of T4 and T3 were lower than the normal reference range established for this laboratory in 23 and 39%, respectively, of Alaskan sled dogs tested before the race. Plasma thyroid hormone concentrations frequently are below normal in conditioned Alaskan sled dogs and are further reduced after prolonged submaximal exercise. [source] Pharmacokinetics of total thyroxine in dogs after administration of an oral solution of levothyroxine sodiumJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 2 2008G. LE TRAON Oral l -thyroxine (l -T4) supplementation is used to replace thyroid hormone concentrations in dogs with hypothyroidism. The pharmacokinetics of l -T4 following administration of a solution (Leventa®) was investigated in healthy dogs. l -T4 was absorbed fairly rapidly (tmax 3 h). A mean bioavailability of 22% was calculated following a single oral administration of 40 ,g l -T4/kg body weight. Repeated oral administration at the same dose for 14 consecutive days did not lead to any accumulation of T4 in serum. After intravenous administration of l -T4, a serum half-life of 11.6 h was calculated. Food intake concomitant with l -T4 oral administration delayed l -T4 absorption and decreased its rate and extent by about 45%. The relative bioavailability of l -T4 following administration of a tablet formulation was about 50% of that of the l -T4 solution. The pharmacokinetic properties of liquid l -T4 after oral administration support the use of a dose rate of 20 ,g/kg once daily, as a starting dose for replacement therapy in dogs with hypothyroidism. [source] Peri-operative oral triiodothyronine replacement therapy to prevent postoperative low triiodothyronine state following valvular heart surgeryANAESTHESIA, Issue 8 2009Y. S. Choi Summary This study evaluated the effect of oral triiodothyronine (T3) replacement therapy, starting on the day of the surgery, on thyroid hormone concentrations and clinical outcome in high-risk patients undergoing valvular heart surgery. Fifty patients were randomly allocated to either T3 or placebo. In the treatment (T3) group patients received 20 ,g of oral or nasogastric T3 every 12 h starting just before induction of anaesthesia and until the first day after surgery. T3 concentrations were significantly higher in the T3 group than the placebo group from 1 to 36 h after removal of the aortic cross clamp. The number of patients requiring vasopressin after discontinuing cardiopulmonary bypass was significantly greater in the placebo group than the T3 group. Significantly fewer patients required vasopressors in the T3 group on the first day after surgery. [source] Maternal thyroid hormone concentration during late gestation is associated with foetal position at birthCLINICAL ENDOCRINOLOGY, Issue 5 2009Hennie A. Wijnen Summary Objective, To evaluate whether there is an association between maternal thyroid hormone and foetal cephalic head position at term gestation. Context, Rotation and flexion of the head enables the foetus to negotiate the birth canal. Low-normal range thyroid hormone concentrations in euthyroid pregnant women constitute a risk of infant motor abnormality. We hypothesized that low normal maternal thyroid hormone levels are associated with increased risk of abnormal foetal position at delivery. Design, In 960 healthy Dutch women with term gestation and cephalic foetal presentation, thyroid parameters [foetal T4 (FT4), TSH and thyroid peroxidase antibody] were assessed at 36 weeks of gestation, and related to foetal head position (anterior cephalic vs. abnormal cephalic) and delivery mode (spontaneous vs. assisted delivery). Results, Women presenting in anterior position (n = 891) had significantly higher FT4 levels at 36 weeks of gestation than those with abnormal cephalic presentation (n = 69). There were no between-group differences for TSH. Regression analyses indicated that the risk of abnormal head position decreased as a function of increasing FT4 [single odds ratio (OR) = 0·87, 95% confidence intervals (CI) 0·77,0·98; multivariate OR = 0·88, 95% CI 0·72,0·99)]. A similar inverse relationship between maternal FT4 and risk of assisted delivery was obtained (OR = 0·86, 95% CI 0·79,0·95; OR = 0·91, 95% CI 0·84,0·98). Conclusion, The lower the maternal FT4 concentration at 36 weeks of gestation, the higher the risk of abnormal cephalic foetal presentation and assisted delivery. [source] TSH concentration within the normal range is associated with cognitive function and ADHD symptoms in healthy preschoolersCLINICAL ENDOCRINOLOGY, Issue 6 2007Mar Įlvarez-Pedrerol Summary Objective, Thyroid hormone concentrations outside the normal range affect brain development, but their specific influence on behaviour and mental abilities within normal values is unknown. The objective of this study was to investigate whether thyroid hormone concentrations are related to neurodevelopment and ADHD (attention deficit and hyperactivity disorder) symptoms in healthy preschoolers. Design subjects and measurements, Children from two general population birth cohorts in Menorca (n = 289) and Ribera d'Ebre (n = 53), Spain, were assessed in a cross-sectional study at the age of 4. Thyroid hormones (free T4 and T3) and TSH concentrations were measured and mental and motor development was assessed using McCarthy's scales for neuropsychological outcomes and ADHD-DSM-IV for attention deficit and hyperactivity/impulsivity symptoms. Results, Children with TSH concentrations in the upper quartile of the normal range performed lower on McCarthy's scales and were at higher risk for attention deficit and hyperactivity/impulsivity symptoms. In the Menorca cohort, a decrease of 5·8 (P < 0·05) and 6·9 (P < 0·01) points was observed in memory and quantitative skills, respectively. In contrast, high T4 concentrations were associated with decreased risk of having 1,5 attention deficit symptoms (odds ratio: 0·25; P < 0·01); these findings were observed in both cohorts despite differences in mean TSH concentrations. No associations were observed with T3. Conclusions, Despite being within the normal range, high TSH concentrations are associated with a lower cognitive function and high TSH and low free T4 with ADHD symptoms in healthy preschoolers. Statistically significant differences were observed in the highest quartiles of TSH, suggesting a need for re-evaluation of the upper limit of the normal TSH range. [source] Hyperthyroidism is characterized by both increased sympathetic and decreased vagal modulation of heart rate: evidence from spectral analysis of heart rate variabilityCLINICAL ENDOCRINOLOGY, Issue 6 2006Jin-Long Chen Summary Objective, The clinical manifestations of hyperthyroidism resemble those of the hyperadrenergic state. This study was designed to evaluate the impact of hyperthyroidism on the autonomic nervous system (ANS) and to investigate the relationship between serum thyroid hormone concentrations and parameters of spectral heart rate variability (HRV) analysis in hyperthyroidism. Design and patients, Thirty-two hyperthyroid Graves' disease patients (mean age 31 years) and 32 sex-, age-, and body mass index (BMI)-matched normal control subjects were recruited to receive one-channel electrocardiogram (ECG) recording. Measurements, The cardiac autonomic nervous function was evaluated by the spectral analysis of HRV, which indicates the autonomic modulation of the sinus node. The correlation coefficients between serum thyroid hormone concentrations and parameters of the spectral HRV analysis were also computed. Results, The hyperthyroid patients revealed significant differences (P < 0·001) compared with the controls in the following HRV parameters: a decrease in total power (TP), very low frequency power (VLF), low frequency power (LF), high frequency power (HF), and HF in normalized units (HF%); and an increase in LF in normalized units (LF%) and in the ratio of LF to HF (LF/HF). After correction of hyperthyroidism in 28 patients, all of the above parameters were restored to levels comparable to those of the controls. In addition, serum thyroid hormone concentrations showed significant correlations with spectral HRV parameters. Conclusions, Hyperthyroidism is in a sympathovagal imbalanced state, characterized by both increased sympathetic and decreased vagal modulation of the heart rate. These autonomic dysfunctions can be detected simultaneously by spectral analysis of HRV, and the spectral HRV parameters could reflect the disease severity in hyperthyroid patients. [source] The quantity of thyroid hormone in human milk is too low to influence plasma thyroid hormone levels in the very preterm infantCLINICAL ENDOCRINOLOGY, Issue 5 2002Aleid G. Van Wassenaer Summary background Thyroid hormone is crucial for brain development during foetal and neonatal life. In very preterm infants, transient low levels of plasma T4 and T3 are commonly found, a phenomenon referred to as transient hypothyroxinaemia of prematurity. We investigated whether breast milk is a substantial resource of thyroid hormone for very preterm neonates and can alleviate transient hypothyroxinaemia. Both the influence of breast feeding on plasma thyroid hormone levels and the thyroid hormone concentration in preterm human milk were studied. methods Two groups were formed from the placebo group of a randomized thyroxine supplementation trial in infants born at < 30 weeks' gestational age on the basis of the mean breast milk intake during the third, fourth and fifth weeks of life. One group received more than 50% breast milk (mean breast milk intake 84%, n = 32) and the other group less than 25% breast milk (mean breast milk intake 3·3%, n = 25). Plasma thyroid hormone concentrations were compared between the two groups. Breast milk was collected from mothers of infants participating in the same trial and the thyroxine concentration in breast milk was measured with RIA after extraction. results No significant differences were found between both groups in plasma concentrations of T4, free T4, T3, TSH, rT3 and thyroxine-binding globulin (TBG), which were measured once a week. Thyroxine concentration in breast milk ranged between 0·17 µg/l and 1·83 µg/l (mean 0·83, SD 0·3 µg/l) resulting in a maximum T4 supply of 0·3 µg/kg via ingested breast milk. In formula milk, the T4 concentration was equally low. Protease treatment did not influence the measured T4 concentrations. conclusions No differences in plasma thyroid hormone between breast milk-fed and formula-fed infants were found. The amount of T4 present in human milk and formula milk is too low to alter the hypothyroxinaemic state of preterm infants. [source] | |||||||||||||