Plasma Thyroxine Levels Research Articles

Altered Thyroid Hormones and Behavioural Change in a Sub‐Population of Rats Following Chronic Constriction Injury

Hypothyroidism is associated with a disturbance of behaviour and mood. There are also individuals, not classified as hypothyroid, with low to 'low normal' thyroid hormone levels and normal thyroid-stimulating hormone (TSH) levels who have mood and behavioural changes. As the peripheral thyroid hormones decrease, TSH is expected to increase. However, there are a number of physiological mechanisms known to suppress TSH. In the present study, we report on thyroid hormone regulation in a rat model of neuropathic pain and altered social behaviour that is usually transient, but is persistent in a sub-group of the population. Following ligation of the sciatic nerve, male Sprague-Dawley rats were assessed for social dominance towards an intruder: 20% showed persistently decreased social dominance. Plasma levels of thyroid hormones, TSH and corticosterone were measured before and on days 2, 3, 4, 5 and 6 after injury in 21 rats. The mean plasma thyroxine (T4), free thyroxine (fT4) and triiodothyronine (T3) levels decreased significantly post-injury in rats with persistently changed behaviour compared to rats with unchanged behaviour (P < or = 0.002). There was no significant difference between groups for mean change in free triiodothyronine (fT3) or TSH. There was a correlation between decreased dominance behaviour and decrease in both T4 (r = 0.62, P = 0.009) and fT4 (r = 0.71, P = 0.001), but no correlation with TSH. In a sub-population of rats, decreased thyroid hormones did not result in the expected increased levels of TSH to restore pre-injury levels, nor did they show increased hypothalamic thyrotrophin-releasing hormone mRNA expression, indicating altered hypothalamic-pituitary-thyroid axis regulation. Because T3 availability to the brain is dependent on both circulating T3 and T4, decreased peripheral thyroid hormones may result in changed neural function, as expressed in altered complex behaviours in this sub-population of rats.

Triclosan and Anuran Metamorphosis: No Effect on Thyroid-Mediated Metamorphosis in Xenopus laevis

Nieuwkoop and Faber stage 51 Xenopus laevis larvae were exposed for 21 days to four different concentrations of triclosan (TCS): <0.2 (control), 0.6, 1.5, 7.2, or 32.3 microg TCS/l. Primary endpoints were survival, hind limb length, body length (whole; snout to vent), developmental stage, wet whole body weight, and thyroid histology. Thyroid hormone (TH) concentrations were determined in whole thyroid and plasma samples from stage-matched exposure day 21 specimens. TH receptor-beta (TRbeta) expression was measured in stage-matched tail fin tissue samples collected at exposure days 0 and 21. Reduced larval growth occurred at exposure day 21 with 1.5 microg/l treatment. Larval developmental stage at exposure day 21 was not significantly different from controls based on observed parameters. Thyroid histology was not affected by TCS, and thyroxine (T4) levels in thyroid glands or plasma were not different from controls. A concentration-dependent increase in TRbeta expression in exposure day 21 larvae was not detected. However, increased expression was found in stage-matched larvae exposed to 1.5 or 7.2 microg TCS/l. Our study indicates that environmentally relevant TCS concentrations do not alter the normal course of thyroid-mediated metamorphosis in this standard anuran model.

Developmental delays consistent with cochlear hypothyroidism contribute to failure to develop hearing in mice lacking Slc26a4/pendrin expression

Mutations of SLC26A4 cause an enlarged vestibular aqueduct, nonsyndromic deafness, and deafness as part of Pendred syndrome. SLC26A4 encodes pendrin, an anion exchanger located in the cochlea, thyroid, and kidney. The goal of the present study was to determine whether developmental delays, possibly mediated by systemic or local hypothyroidism, contribute to the failure to develop hearing in mice lacking Slc26a4 (Slc26a4(-/-)). We evaluated thyroid function by voltage and pH measurements, by array-assisted gene expression analysis, and by determination of plasma thyroxine levels. Cochlear development was evaluated for signs of hypothyroidism by microscopy, in situ hybridization, and quantitative RT-PCR. No differences in plasma thyroxine levels were found in Slc26a4(-/-) and sex-matched Slc26a4(+/-) littermates between postnatal day 5 (P5) and P90. In adult Slc26a4(-/-) mice, the transepithelial potential and the pH of thyroid follicles were reduced. No differences in the expression of genes that participate in thyroid hormone synthesis or ion transport were observed at P15, when plasma thyroxine levels peaked. Scala media of the cochlea was 10-fold enlarged, bulging into and thereby displacing fibrocytes, which express Dio2 to generate a cochlear thyroid hormone peak at P7. Cochlear development, including tunnel opening, arrival of efferent innervation at outer hair cells, endochondral and intramembraneous ossification, and developmental changes in the expression of Dio2, Dio3, and Tectb were delayed by 1-4 days. These data suggest that pendrin functions as a HCO3- transporter in the thyroid, that Slc26a4(-/-) mice are systemically euthyroid, and that delays in cochlear development, possibly due to local hypothyroidism, lead to the failure to develop hearing.

Calcitonin Inhibits TRH-Induced TSH Secretion

The authors investigated in 14 healthy volunteers the effect of a single dose of 50 MRCU of synthetic salmon calcitonin on plasma levels of thyroxine (T4), triiodothyronine (T3), thyrotropin (TSH), calcium, phosphorus and magnesium and on the thyrotropic secretory reserve assessed by means of the TRH test. T4 and T3 levels did not change significantly within 120 min after administration of calcitonin. TSH levels during the 60th minute declined insignificantly. TRH stimulated TSH levels after administration of calcitonin were significantly lower, as compared with control values (p less than 0.01). The thyrotrophic secretory reserve determined as the difference of TSH values at rest and after stimulation was significantly inhibited by calcitonin (p less than 0.01). The phosphorus and magnesium levels did not change significantly after calcitonin, the calcium levels displayed only a slightly declining trend. No correlation was revealed between the secretory response of TSH and calcium, phosphorus and magnesium levels. The inhibitory action of calcitonin on TSH secretion is probably not mediated by changes in the extracellular concentration of these ions but is most probably the consequence of the direct influence on the secretory mechanism inside the thyrotrophic cell.

Hard nut to crack in diagnosis of pituitary hyperplasia secondary to primary hypothyroidism and reasons of misdiagnosis

To analyze the difficulty in diagnosis of pituitary hyperplasia secondary to primary hypothyroidism and reasons of misdiagnosis. Ten patients with clinical manifestations of primary hypothyroidism, 3 males and 7 females, aged 7 - 26, underwent MR imaging and serum hormone examination before and after thyroid hormone replacement therapy. T1-weighted images without and with contrast material enhancement in sagittal and coronal planes were obtained. Serum free triiodothyronine, free thyroxine, thyrotropic-stimulating hormone and prolactin (PRL) levels were measured. Obvious symmetrical enlargement of the pituitary gland with homogeneous signal intensity was revealed by MRI in all the patients. The height of the pituitary ranged 1.2 - 2.2 cm. The pituitary glands appeared homogeneously enhanced after Gd-DTPA administration. After 3 - 6 months of L-thyroxin replacement therapy, follow-up MRI showed that the pituitary glands reduced in size markedly in 9 cases, and the plasma thyroxine, TSH, and PRL levels of these 9 cases turned normal. One patient was misdiagnosed as with macroadenoma and was treated with gamma knife, resulting in permanence hypothyroidism. Symmetrical enlargement of pituitary gland with homogeneously enhancement on MRI has great diagnostic value in pituitary hyperplasia with primary hypothyroidism. Thyroid hormone replacement therapy can cause regression of the enlarged pituitary, thus avoiding unnecessary surgery.

Hormonal Correlates and Thermoregulatory Consequences of Molting on Metabolic Rate in a Northerly Wintering Shorebird

Even though molt involves both endocrine and energetic changes in bird bodies, this study is among the first to combine assessments of energy costs together with thyroid hormone variations in molting birds. Individual shorebirds (red knots Calidris canutus islandica) were measured while in full summer and winter plumage as well as during peak of molt. Molt was associated with a 9.8% increase in average mass-independent basal metabolic rate (BMR) above nonmolting levels. Individual plasma levels of thyroxine (T(4)) were correlated with individual rate of body feather renewal, confirming that T(4) is related to body molt but also showing that it is potentially regulating its rate. Across seasons, mass-independent average heat loss measured as conductance gradually declined with conductance during molt falling between measured values for summer and winter. During the molting period, however, body molting rate was positively correlated with thermal conductance, indicating that for a given ambient temperature below thermoneutrality, the fastest molting birds were losing more body heat. Across seasons, triiodothyronine (T(3)), a hormone typically upregulated in response to a cold stimulus, was correlated with individual thermal conductance and BMR. We suggest that the increased heat loss of fast-molting birds leads to a cold-acclimatization response that may be partly responsible for the elevated BMR measured during molt. This could be mediated through a stimulatory effect of T(3) on BMR in response to increased heat loss. Our interpretation is supported by a positive relationship between the individual changes in conductance and the change in BMR from summer to the molting period.

Evaluation of Endocrine Disrupting Effects of Nitrate after In Utero Exposure in Rats and of Nitrate and Nitrite in the H295R and T-Screen Assay

Animal studies have shown that nitrate acts as an endocrine disrupter affecting the androgen production in adult males. This raises a concern for more severe endocrine disrupting effects after exposure during the sensitive period of prenatal male sexual development. As there are no existing studies of effects of nitrate on male sexual development, the aim of the study was to examine how in utero exposure to nitrate would affect male rat fetuses. Pregnant dams were dosed with nitrate in the drinking water from gestational day (GD) 7 to GD21 at the following dose levels 17.5, 50, 150, 450, and 900 mg/l. At GD21, fetuses were examined for anogenital distance, plasma thyroxine levels, testicular and plasma levels of testosterone and progesterone, and testicular testosterone production and histopathology. In addition, endocrine disrupting activity of nitrate and nitrite were studied in two in vitro assays, the H295R assay and T-screen. There were no consistent indications that nitrate induces anti-androgenic effects in male fetuses or that prenatal nitrate exposure affected the thyroid axis. However, a more comprehensive study with long-term exposure before and during pre- and postnatal development would be relevant to sufficiently address the concerns based on the indications for endocrine disrupting effects in adult animals.

Effects of Simulated Hypo‐ and Hyper‐Reproductive Conditions on the Characteristics of Circadian Rhythm in Hypothalamic Concentration of Serotonin and Dopamine and in Plasma Levels of Thyroxine, Triiodothyronine, and Testosterone in Japanese Quail, Coturnix coturnix japonica

In this study, hypo‐ and hyper‐reproductive conditions, as measured by concentrations of plasma testosterone in male Japanese quail held on long days LD 16:8, were experimentally simulated with injections of 5‐hydroxytryptophan (5‐HTP) and L‐dihydroxyphenylalanine, (L‐DOPA) with 8 h and 12 h phase angle differences between them in intact and melatonin‐treated birds. The effects of these treatments were assessed on the characteristics of the circadian rhythm in the hypothalamic concentration of serotonin (5‐HT), dopamine (DA), and plasma levels of thyroxine (T4), triiodothyronine (T3), and testosterone (T). These rhythms were also studied in sham‐operated (SO), pinealectomized (Px), vehicle‐ (Veh), and melatonin (Mel)‐treated birds. On the basis of the circadian mesors of the testosterone rhythms, three distinct categories could be identified: category A (i.e., normal breeding concentrations of plasma testosterone), which includes control, sham‐operated, and vehicle‐treated groups; category A+ (i.e., concentrations of plasma testosterone higher than that found in normal breeding quail), which includes 12 h, 12 h+vehicle‐treated, and Px quails; and category A− (concentrations of plasma testosterone lower than that found in normal breeding quail), which includes 8 h, melatonin‐, and 12 h+melatonin‐treated groups. It is evident that in normal and hypergonadal conditions (i.e., birds belonging to categories A and A+) the circadian rhythm in hypothalamic serotonin maintained a positive phase angle of about 16 h. In contrast, birds of category A− (i.e., in a hypogonadal condition) exhibited a negative phase angle of about 2 h. The present results clearly suggest that the internal phase relationship between the circadian rhythms in hypothalamic serotonin and dopamine might play a crucial role in strategizing and conferring a particular reproductive status to the birds. The role of circadian mechanisms involving circulating thyroid hormones in conferring reproductive status is completely ruled out, as no definite internal phase angle between these two hormonal rhythms was witnessed vis‐à‐vis different treatment groups. The testosterone peaks always occurred at the same time irrespective of breeding status of the bird, but with significant variation in its amplitude (high in hypergonadal and low in hypogonadal condition). It is suggested that administration of 5‐HTP and L‐DOPA at specific time interval and variation in pineal functions that modulate reproductive responses also alter the circadian pattern (acrophase and amplitude) of hypothalamic serotonin and dopamine, maintaining a specific phase relation between these cycles and breeding status. These findings strengthen our previous reports that a specific circadian phase relation of serotonergic and dopaminergic oscillations regulates reproduction. The present study strongly supports interdependence and specific relation of the two systems (gonadal activity and circadian pattern/phase relation of neural oscillation) in both natural and experimentally simulated conditions.

The impact of a pesticide on the physiology and behaviour of hatchery‐reared Atlantic salmon, Salmo salar, smolts during the transition from fresh water to the marine environment

Abstract Atlantic salmon, Salmo salar L., smolts were exposed to environmental levels of the pesticide atrazine in a hatchery, tagged with acoustic transmitters and released into fresh water at the peak of the smolt run. The subsequent movements of the smolts were monitored within the freshwater and immediate coastal zones using an array of acoustic receivers. In laboratory‐based studies, exposure to a 0.1 μg L−1 concentration of atrazine over a 72‐h period significantly reduced gill Na+K+ATPase activity but not plasma thyroxine (T4) and triiodothyronine (T3) levels compared with the control group, and on transfer to 33‰ saltwater resulted in 100% mortality. However, exposure to atrazine did not have a significant effect on the subsequent movements of the smolts in the freshwater, estuarine and marine environments. The results are discussed in relation to the impact of diffuse pollution on salmon populations.

O.472 Ultrasound activated pin flxation in pediatric maxillo-facial traumas

Maternal thyroid hormones (THs) play an essential role in the embryonic and larval development of fish. Previous studies in fish have reported that parental exposure to thyroid disrupting chemicals (TDCs) changed maternal TH levels in the offspring; however, whether this transgenerational thyroid endocrine disruption can further disturb the early development of the offspring still remains largely unknown. Bisphenol S (BPS), a substitute of bisphenol A, has been reported to be a potential TDC. In this study, zebrafish (F0) were exposed to environmentally relevant concentrations (1, 10, and 100 μg/L) of BPS from 2 h post-fertilization to 120 days post-fertilization and then paired to spawn. Plasma levels of thyroxine (T4) were significantly decreased in F0 females while 3,5,3′-triiodothyronine (T3) plasma levels were significantly increased in F0 females and males; moreover, TH content in eggs (F1) spawned by exposed F0 generation exhibited similar changes as the F0 females, with significant decreases in T4 and increases in T3, demonstrating BPS-induced maternal transfer of thyroid endocrine disruption. Further, excessive levels of maternal T3 in the offspring resulted in delayed embryonic development and hatching, swim bladder inflation defect, reduction in motility, developmental neurotoxicity, and lateral stripe hypopigmentation in non-exposed F1 embryos and larvae. These results highlight the adverse effects on the early development of offspring induced by transgenerational thyroid endocrine disruption, which have been ignored by previous studies. Therefore, these results can further improve our understanding of the ecological risks of TDCs.

Toxicity of analytically cleaned pentabromodiphenylether after prolonged exposure in estuarine European flounder ( Platichthys flesus), and partial life-cycle exposure in fresh water zebrafish ( Danio rerio)

Residues of polybrominated diphenylethers (PBDEs), extensively applied as flame retardants, are widely spread in the aquatic environment and biota. The present study investigates effects of the environmentally relevant lower brominated diphenylethers in two fish species in vivo under controlled laboratory conditions. Euryhaline flounder ( Platichthys flesus) and freshwater zebrafish ( Danio rerio) were exposed to a range of concentrations of a commercial pentabromodiphenylether mixture, DE-71. Chemical analysis of exposed fish showed a pattern of PBDE congeners that was very similar to that in wild fish. The resulting range included environmentally relevant, as well as higher levels. Animals were investigated histopathologically with emphasis on endocrine and reproductive organs. In zebrafish, hatching of embryos and larval development were assessed. Biochemical parameters were investigated in flounder as markers for suggested dioxin-like activity (ethoxyresorufin- O-deethylase = EROD), and activation of endogenous estrogen synthesis (gonad aromatase activity). Thyroid hormones were analyzed in plasma in both species. Benchmark analysis using internal PBDE concentrations showed a mild dose-dependent decrease of hepatic EROD and ovarian aromatase activities, and plasma thyroxin levels in flounder, and an increase of plasma thyroid hormone levels in zebrafish. These trends did not result in statistically significant differences from control fish, and major histopathological changes were not observed. Reproduction in zebrafish appeared to be the most sensitive parameter with statistically significantly reduced larval survival and non-significant indications for decreased egg production at internal levels that were more than 55 times the highest environmental recordings. The present results indicate limited risk for endocrine or reproductive effects of current environmental PBDE contamination in fish.

Provisional clinical chemistry parameters in the African Sharptooth catfish (&lt;i&gt;Clarias gariepinus&lt;/i&gt;)

Pollution affects aquatic systems worldwide and there is an urgent need for efficient monitoring. Fish are generally sensitive to their environment and are thus considered to be valuable bioindicator species. The African Sharptooth catfish (Clarias gariepinus) is particularly important in this respect because of its very wide distribution. In order to use C. gariepinus as a bioindicator species its baseline clinical chemistry must be defined. Existing data are scarce, and the objective of this work was therefore to establish clinical chemistry parameters for C. gariepinus. Blood was collected from male and female catfish and a number of clinical chemistry parameters were determined. Plasma protein values, but particularly those of plasma albumin, were found to be very low, approximately half the value for dogs, but similar to the values in Channel catfish (Ictalurus punctatus). Plasma urea values in Sharptooth catfish were found to be much lower than in dogs, but only marginally lower than in Channel catfish. Plasma creatinine in Sharptooth catfish, however, was only a quarter of that of dogs and one third of that found in Channel catfish. These findings may have implications for using urea and/or creatinine as an index of renal glomerular filtration, as is done in mammals. Plasma enzyme activity ranges were much lower in Sharptooth catfish than in dogs, particularly for alkaline phosphatase (ALP) and alanine aminotransferase (ALT). By comparison, Channel catfish have an even lower ALT activity range but an ALP range that is very similar to dogs. The implications for using these enzymes as markers for liver disease are not clear from these data, as factors such as plasma half-life and tissue distribution remain to be determined. The very low plasma thyroxine (T4) levels have important implications for laboratory personnel, who will have to set up calibration and standardisation adaptations for the methods that are generally designed for human samples. Although the sample size was too small for reliable comparisons, it appeared that there was little difference in the parameters measured between male and female fish. The values obtained are a useful starting point for using C. gariepinus as a bioindicator species.

Regulation of liver cytochrome P450 by activation of brain dopaminergic system: Physiological and pharmacological implications

The aim of the present study was to investigate the influence of activation of brain dopaminergic system by different dopaminomimetics on the level and activity of liver cytochrome P450 (CYP) isoforms. Studies into the identification of hormones and cytokines which are known to mediate liver CYP expression were also simultaneously carried out. Stimulation of dopaminergic receptors in the pituitary, a target for the tuberoinfundibular pathway, by dopamine (a D 1/D 2 receptor agonist) administered intraperitoneally caused a significant increase in the activities and protein levels of CYP2B, CYP2C11 and CYP3A, a substantial increase in the blood plasma level of growth hormone (GH) and a significant decrease in triiodothyronine (T 3) level. Local stimulation of dopaminergic receptors in the nucleus accumbens, a target for the mesolimbic pathway, by apomorphine (a D 1/D 2 receptor agonist), amphetamine (an indirect D 1/D 2 dopaminemimetic) and quinpirole (a D 2 receptor agonist) produced a substantial rise in CYP3A activity and protein level, caused a large increase in corticosterone concentration and a moderate drop in T 3 level. SKF82958 (a D 1 receptor agonist) did not significantly affect the CYP isoforms or hormones studied. In both cases (activation of the tuberoinfundibular or mesolimbic pathway), the activity and the protein level of CYP1A considerably decreased. Plasma levels of thyroxine, testosterone, interleukin-2 and interleukin-6 were not changed after activation of the two pathways. The obtained results establish the brain dopaminergic system as a physiological centre regulating cytochrome P450 (engaging D 2 receptors and pituitary hormones) and demonstrate new pharmacological aspects of neuroactive drugs that affect this system.

Plasma Thyroxine and Cortisol Profiles and Gill and Kidney Na+/K+-ATPase and SDH Activities During Acclimation of the Catfish Heteropneustes fossilis (Bloch) to Higher Salinity, with Special Reference to the Effects of Exogenous Cortisol on Hypo-Osmoregulatory Ability of the Catfish

When the stenohaline catfish Heteropneustes fossilis was transferred from fresh water (FW) to 30% seawater (SW), the Na(+)/K(+)-ATPase activity significantly increased in the kidney, while in gills it remained more or less constant. A reverse pattern was observed for succinic dehydrogenase (SDH) activity inasmuch as it significantly increased in gills and remained unchanged in the kidney. Plasma osmolality significantly increased within 3 days of transfer to 30% SW and remained significantly higher throughout the duration of experiment. These results suggest that catfish gills may not be able to reverse their function from salt uptake in FW to salt excretion at higher salinity, and that the elimination of monovalent as well as divalent ions is performed by the kidney but not the gills. The significant decline in plasma cortisol (F) levels following transfer to higher salinity may not be due to reduced production but rather to an enhanced utilization and clearance rate, a conclusion supported by the fact that exogenous administration of cortisol acetate (FA) resulted in significant increases in branchial and renal Na(+)/K(+)-ATPase in FW and 30% SW. FA also improved the plasma osmotic regulatory ability of the catfish, possibly due to a change in branchial function from salt-absorption to salt excretion, as was evident from a significant increase in branchial Na(+)/K(+)-ATPase activity in the fish in 30% SW pretreated with FA for 5 days. Consistently higher levels of plasma thyroxine (T4) following transfer to higher salinity suggest the involvement of this hormone at higher salinity.

The parr–smolt transformation of Arctic charr is comparable to that of Atlantic salmon

The present study was undertaken to investigate endocrine and osmoregulatory changes during the parr–smolt transformation of anadromous Arctic charr (Salvelinus alpinus). One year old, first generation hatchery-reared offspring of wild anadromous Arctic charr were kept at natural temperatures and a short daylength (10 h) during winter and continuous light from March until the end of the experiment in late June. At regular intervals, fish were sampled in freshwater for measuring gill Na+,K+-ATPase activity and the plasma levels of hormones known to be involved in smoltification, whereas other fish were exposed to 24-h seawater challenge tests for investigation of their hypoosmoregulatory ability. From mid-May onwards, there was an abrupt, and strong improvement in the fish's hypoosmoregulatory ability, concomitant with an increase in gill Na+,K+-ATPase activity. The development of hypoosmoregulatory ability was preceded by increased growth hormone (GH) levels from March to April, a continuous increase in insulin-like growth factor-I (IGF-I) levels from March to mid-June, and a transient increase in cortisol levels in parallel with the increase in gill Na+,K+-ATPase activity. These results support the roles of these hormones in stimulating the ion secreting machinery of the gills, and are in line with those considered typical for parr–smolt transforming Atlantic salmon (Salmo salar). A strong decrease in plasma thyroxine (T4) levels during the last part of the smoltification period deviates from the often reported increase in this parameter in parr–smolt transforming Atlantic salmon and supports the view that this hormone has a permissive or supportive role only in teleost salinity adaptation. To conclude, the parr–smolt transformation of the anadromous Arctic charr strain used in the present study resembles that of Atlantic salmon, both with regard to the development of hypoosmoregulatory ability and regulatory (endocrine) mechanisms.

Influence of dietary fats on ecstasy‐induced hyperthermia

Studies were designed to examine the effects of dietary fats on metabolic effects of 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy). These effects included hyperthermia, expression of uncoupling protein (UCP1 and 3) in brown adipose tissue or skeletal muscle and plasma free fatty acid (FFA) levels. Male Sprague-Dawley rats were fed either a high-fat diet (HFD, 60% kcal) or a lower fat isocaloric controlled diet (LFD, 10% kcal) for 28 days before MDMA challenge. No significant differences were observed between LFD and HFD groups in terms of body weight, plasma thyroxine (T4) levels and expression of brown fat UCP1 or skeletal muscle UCP3 protein. HFD significantly raised levels of circulating FFA and potentiated the thermogenesis induced by MDMA (10 mg kg(-1), s.c.), compared to the effects of the LFD. Moreover, 30 and 60 min after MDMA administration, plasma FFA levels decreased in HFD animals, but were markedly elevated in the LFD group. These results indicate that high-fat feeding regulates MDMA-induced thermogenesis by augmenting the activation of UCP rather than its expression.

Thyroid hormone level and relative liver weight in male turkeys in relationship with their welfare

The objective assessment of poultry welfare is presently a global problem, which is directly related to poultry products. The investigations on the possibilities for evaluation of the physiological comfort of turkeys by the use of alternative indicators are scarce. The aim of the present study was to determine the reliability of liver weight and thyroid hormone level in male turkeys from Local Bulgarian hybrid as indicators of their welfare. Plasma thyroxine levels were determined by radioimmunoassay method (RIA). The relative liver weights and plasma thyroxine levels of the I-st group turkeys (Local hybrid, reared on the litter) were significantly higher than in the II-nd one (Local hybrid, reared on the slat floor). A correlation between plasma thyroxine levels and plasma corticosterone levels in male turkeys, raised on the litter was established. A close relationship was found between liver weight, plasma thyroxine levels and the status of poultry welfare.

Increasing plasma thyroxine levels during late embryogenesis and hatching in the chicken are not caused by an increased sensitivity of the thyrotropes to hypothalamic stimulation

The hatching process in the chicken is accompanied by dramatic changes in plasma thyroid hormones. The cause of these changes, though crucial for hatching and the onset of endothermy, is not known. One hypothesis is that the pituitary gland becomes more sensitive to hypothalamic stimulation during this period. We have tested whether the responsiveness of the thyrotropes to hypothalamic stimuli changes throughout the last week of embryonic development and hatching by studying the mRNA expression of receptors involved in the control of the secretory activity of this cell type. We used a real-time PCR set-up to quantify whole pituitary mRNA expression of the beta subunit of thyrotrophin (TSH-beta), type 1 thyrotrophin-releasing hormone receptor (TRH-R1), corticotrophin-releasing hormone receptors (CRH-R1 and CRH-R2) and somatostatin subtype receptor 2 (SSTR2) on every day of the last week of embryonic development, including the day of hatch and the first day of posthatch life. The thyrotrope-specific expression was investigated by a combination of in situ hybridization with immunohistochemistry at selected ages. Although TSH-beta mRNA levels increased towards day 19 of incubation (E19), the expression of CRH-R2 and TRH-R1 mRNA by the thyrotropes tended to decrease during this period, suggesting a lower sensitivity of the thyrotropes to the stimulatory factors CRH and TRH. CRH-R1, which is not involved in the control of TSH secretion, increased steadily throughout the period tested. The expression of SSTR2 mRNA by the thyrotropes was low during embryonic development and increased just before hatching. We have concluded that the sensitivity of the pituitary thyrotropes to hypothalamic stimulation decreases throughout the last week of embryonic development, so that the higher expression of TSH-beta mRNA around E16-E19, and hence the increasing plasma thyroxine level, is unlikely to be the result of an increased stimulation by either TRH or CRH.

Iodine supplementation for the prevention of mortality and adverse neurodevelopmental outcomes in preterm infants

Parenteral nutrition solutions, formula milks, and human breast milk contain insufficient iodine to meet recommended intakes for preterm infants. Iodine deficiency may exacerbate transient hypothyroxinaemia in preterm infants and this may be associated with adverse respiratory or neurological outcomes. To assess the evidence from randomised controlled trials that dietary supplementation with iodine reduces mortality and morbidity in preterm infants. We used the standard search strategy of the Cochrane Neonatal Review Group. This included searches of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 4, 2005), MEDLINE (1966 - November 2005), EMBASE (1980 - November 2005), CINAHL (1982 - November 2005), conference proceedings, and previous reviews. Randomised or quasi-randomised controlled trials that compared a policy of supplementing enteral or parenteral feeds with iodine (more than 30 micrograms per kilogram per day) versus placebo or no supplementation in preterm infants. The standard methods of the Cochrane Neonatal Review Group, with separate evaluation of trial quality and data extraction by two reviewers, and synthesis of data using relative risk, risk difference and weighted mean difference. The primary outcomes for this review were neonatal mortality, death before hospital discharge, and longer term neurodevelopmental outcomes including severe neurodevelopmental disability. We found only one randomised controlled trial (N = 121) that fulfilled the review eligibility criteria (Rogahn 2000). The participants were infants born before 33 weeks' gestation (but most were of birth weight greater than 1000 grams). The primary aim of this trial was to assess the effect of iodine supplementation on thyroid function. The investigators did not detect any statistically significant effects on the plasma levels of thyroxine (free and total), triiodothyronine, or thyrotrophin in preterm infants (measured up to 40 weeks' post-conceptional age). Only one infant died and the trial was therefore underpowered to detect an effect on mortality. The trial did not assess the effect of the intervention on neurodevelopmental morbidity. There was not a statistically significant difference in the incidence of chronic lung disease. There are insufficient data at present to determine whether providing preterm infants with supplemental iodine (to match fetal accretion rates) prevents morbidity and mortality in preterm infants. Future randomised controlled trials of iodine supplementation should focus on extremely preterm and extremely low birth weight infants, the group at greatest risk of transient hypothyroxinaemia. These trials should aim to assess the effect of iodine supplementation on clinically important outcomes including respiratory morbidity and longer term neurodevelopment.

Reproductive phase dependent circadian variation in hypothalamic concentration of serotonin, dopamine and peripheral thyroxine levels in Japanese Quail following 5-HTP and L-DOPA administration at specific time intervals

Temporal phase relations of circadian hypothalamic neurotransmitters are reported to regulate seasonal reproduction in some avian species. Present experiments were designed to study circadian variation in the hypothalamic concentration of neurotransmitters (serotonin and dopamine) and the plasma thyroxine level in sexually active (long day) and inactive (short day) Japanese Quail. A significant circadian cycle was noted in the hypothalamic content of both serotonin and dopamine, but with different patterns. In breeding Quail, peak activity of serotonin and dopamine was noted at 10.00 A.M. and 10.00 P.M. respectively i.e. at the interval of 12 hours. However, during sexually quiescent condition, peaks of both neurotransmitters occurred at 2.00 P.M. i.e. having a 0-hour temporal relationship. During the breeding phase, the plasma thyroxine level showed a biphasic pattern with two circadian peaks at 10.00 A.M. and 10.00 P.M. whereas in the non-breeding condition a single peak was observed at 10.00 A.M. In the second experiment, to study the effect of temporal synergism of neurotransmitter precursor drugs on circadian cycles, two groups of Quail were administered daily with serotonin precursor 5-HTP (5-hydroxytryptophan) and dopamine precursor L-DOPA (L-dihydroxyphenylalanine) (5 mg/100 g body weight) 12 hour (12-hr) and 8 hour (8-hr) apart over a period of 11 days under continuous conditions of light and then transferred to long day length for 15 days when the experiment was terminated. When compared to controls, the 12-hr condition induced breeding while the 8-hr condition led to a non-breeding condition. The circadian pattern of serotonin levels of control and 12-hr Quail was similar to that of a normal sexually active bird, while that of the 8-hr Quail showed the pattern of a sexually inactive bird. The plasma thyroxine level exhibited a biphasic pattern in 12-hr Quail, which was similar to a normally breeding bird, whereas unlike sexually inactive birds, the thyroxine concentration in 8-hr Quail was relatively low and did not show significant cyclicity. Interestingly, the plasma testosterone level of 12-hr Quail followed a more or less similar pattern with peak activities coinciding with that of thyroxine i.e. biphasic in the sexually active condition (12-hr and control) but a single peak in the quiescent (8-hr) condition. These findings suggest that the temporal phase relation of circadian serotonergic and dopaminergic oscillator varies as a function of reproductive status of the bird, and breeding/non-breeding conditions may be induced experimentally by changing the phase relation of these oscillations.