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1.
Primary congenital hypothyroidism is characterized by low levels of circulating thyroid hormones and raised levels of thyrotropin at birth. It can be either permanent or transitory. Most permanent cases (80-85%) result from alterations in the formation of the thyroid gland during embryogenesis (thyroid dysgenesis), and several were shown recently to be produced by mutations in genes responsible for the development of thyroid follicular cells (TITF1, TITF2, PAX8 and TSHR). Less frequently, congenital hypothyroidism is determined by defects in thyroid hormone synthesis (hormonogenesis defects). The latter are usually associated with goiter. Recently, the molecular mechanisms of two forms of hormonogenesis defects (iodine transport defects and Pendred syndrome) were elucidated. 相似文献
3.
- 1.Following targeted conservation actions most goose populations have increased. The growing goose populations caused an increase in human-wildlife conflicts and have the potential to affect nature values. As meadow birds, including meadow-breeding waders, were declining throughout Western Europe, the possible negative effect of rising numbers of foraging barnacle geese on their breeding success has been questioned.
- 2.We used GPS-transmitter data to measure the density of foraging barnacle geese during daylight hours. Using dynamic Brownian Bridge Movement Models (dBBMM), we investigated the effect of barnacle goose density on the territory distribution of five wader species, and on nest success of the locally common Northern lapwing. We used model selection methods to identify the importance of barnacle goose density related to other environmental factors.
- 3.Our results showed an insignificant positive association between barnacle goose density and nest territory density of the Northern lapwing and common redshank. Barnacle goose density had no influence on territory selection of godwit, oystercatcher and ringed plover. We did, however, find a negative correlation between barnacle geese density and the nest success of the Northern Lapwing.
- 4.We infer that either barnacle goose foraging leads to improved territory conditions for some wader species, or that both barnacle geese and waders prefer the same type of habitat for foraging and nesting. Higher barnacle goose density was correlated with fewer Northern lapwing nests being successful.
- 5.Synthesis and application: Experimental research is needed to disentangle the causal chain, but based on our observational findings, we suggest to increase water logging that may attract both barnacle geese and wader species. Further investigation on the effects of barnacle geese on wader species is necessary to identify the cause of the negative correlation between barnacle geese density and nest success of lapwings; nest protection experiments could give further insight.
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4.
It is well established that a rise in circulating thyroid hormone during the second half of chick embryo development significantly influences muscle weight gain and bone growth. We studied thyroid influence on differentiation in slow anterior latissimus dorsi (ALD) and fast posterior latissimus dorsi (PLD) muscles of embryos rendered hypothyroid by hypophysectomy or administration of an anti-thyroid drug. The expression of native myosins and myosin light chains (MLCs) was studied by electrophoretic analysis, and the myosin heavy chain (MHC) was characterized by immunohistochemistry. The first effects of hypothyroid status were observed at day 21 of embryonic development (stage 46 according to Hamburger and Hamilton). Analysis of myosin isoform expression in PLD muscles of hypothyroid embryos showed persistence of slow migrating native myosins and slow MLCs as well as inhibition of neonatal fast MHC expression, indicating retarded differentiation of this muscle. In ALD muscle, hypothyroidism maintained fast embryonic MHC and induced noticeable amounts of fast MLCs, thus delaying slow muscle differentiation. Our results suggest that thyroid hormones play a role in modulating the appearance of neonatal fast MHC and the disappearance of isomyosins transiently present during embryogenesis. However, T3 supplemental treatment would seem to compensate in part for the effects of hypothyroidism induced by hypophysectomy, suggesting that thyroid hormone might interfere with other factors also accounting for the observed effects. 相似文献
5.
Thyroid hormones (THs) have critical roles in brain development and normal brain function in vertebrates. Clinical evidence suggests that some human nervous disorders involving GABA(gamma-aminobutyric acid)-ergic systems are related to thyroid dysfunction (i.e. hyperthyroidism or hypothyroidism). There is experimental evidence from in vivo and in vitro studies on rats and mice indicating that THs have effects on multiple components of the GABA system. These include effects on enzyme activities responsible for synthesis and degradation of GABA, levels of glutamate and GABA, GABA release and reuptake, and GABA(A) receptor expression and function. In developing brain, hypothyroidism generally decreases enzyme activities and GABA levels whereas in adult brain, hypothyroidism generally increases enzyme activities and GABA levels. Hyperthyroidism does not always have the opposite effect. In vitro studies on adult brain have shown that THs enhance GABA release and inhibit GABA-reuptake by rapid, extranuclear actions, suggesting that presence of THs in the synapse could prolong the action of GABA after release. There are conflicting results on effects of long term changes in TH levels on GABA reuptake. Increasing and decreasing circulating TH levels experimentally in vivo alter density of GABA(A) receptor-binding sites for GABA and benzodiazepines in brain, but results vary from study to study, which may reflect important regional differences in the brain. There is substantial evidence that THs also have an extranuclear effect to inhibit GABA-stimulated Cl(-) currents by a non-competitive mechanism in vitro. The thyroid gland exhibits GABA transport mechanisms as well as enzyme activities for GABA synthesis and degradation, all of which are sensitive to thyroidal state. In rats and humans, GABA inhibits thyroid stimulating hormone (TSH) release from the pituitary, possibly by action directly on the pituitary or on hypothalamic thyrotropin-releasing hormone neurons. In mice, GABA inhibits TSH-stimulated TH release from the thyroid gland. Taken together, these studies provide strong support for the hypothesis that there is reciprocal regulation of the thyroid and GABA systems in vertebrates. 相似文献
6.
To evaluate the role of perinatal thyroid status in the development of pituitary-thyroid axis regulation, we administered triiodothyronine to newborn rats for the first five days postpartum to achieve hyperthyroidism, or propylthiouracil perinatally to rat dams and pups from gestational day 17 through postnatal day 5 to achieve hypothyroidism. Plasma T4, T3, and TSH levels were determined from birth through 50 days postpartum. Administration of exogenous T3 produced the expected immediate suppression of plasma T4 and TSH, with recovery toward normal values beginning within days of discontinuing the T3 regimen. Plasma T3 values were markedly elevated during the period in which T3 was being given, but subsequently became subnormal, with deficits persisting into young adulthood. With the PTU regimen, plasma T4 and T3 levels were markedly suppressed through postnatal day 10, rose over the ensuing two weeks, but nevertheless showed significant deficits into adulthood. TSH levels in the immediate neonatal period were subnormal in the PTU group, despite the marked lowering of circulating thyroid hormones; TSH then rose dramatically to levels four times normal, subsiding to control values by the end of the first month. These results suggest that a critical period exists in which regulation of pituitary-thyroid axis function is programmed. During this phase, TSH secretion can be suppressed by excess thyroid hormones, but cannot be increased by hormone deficiencies. Perhaps more importantly, perinatal thyroid status "programs" its own future reactivity, so that early hypothyroidism results in reduced T4 and T3 levels in adulthood, despite normal levels of TSH. 相似文献
7.
A three-part study explored the basis for an interaction between changes in thyroid status and bulbospinal serotonin (5HT) metabolism. In experiment 1, three well-characterized models of primary hypothyroidism were all accompanied by significant increases in 5HT metabolism. In experiment 2, circulating thyroid hormone levels were experimentally varied from very low methimazole (Meth) treatment to very high (T3 implants: 2.5, 5.0, or 7.5 mg triiodothyronine). As in experiment 1, Meth led to elevated 5HT. Hyperthyroidism was accompanied by significant reductions in 5HT, while urinary norepinephrine excretion paralleled 5HT. In experiment 3, rats were subjected to Meth either 2 weeks before or after induction of diabetes with streptozotocin (Stz). Meth prevented Stz-associated reductions in 5HT and attenuated development of hyperphagia. Meth could not reverse established Stz-associated reduction in 5HT or hyperphagia, although both were slightly attenuated. Thus, although the first two experiments argue for a simple inverse relationship between circulating thyroid hormone levels and 5HT in the brain, experiment 3 demonstrated that Stz-associated decrements in 5HT could not be reversed by subsequent lowering of circulating thyroid hormone. Nor did accompanying measurements indicate that glycemic status or circulating levels of leptin were important predictors of 5HT. Thus the interaction between thyroid hormones and 5HT is both more subtle and more complex than previously thought. 相似文献
8.
Serum bone gamma-carboxyglutamic acid-containing (Gla) protein (BGP) was measured before and with initially 2 weeks, later 4-8 weeks intervals for 20-58 weeks during treatment of patients with hyperthyroidism (n = 10) and hypothyroidism (n = 4). Biochemical euthyroidism was obtained in the hyperthyroid patients after a median of 3 weeks (range 1-8 weeks), and in the hypothyroid patients after a median of 17 weeks (range 10-27 weeks). Serum BGP levels closely followed the thyroid state, being high respectively low in the hyperthyroid and hypothyroid state and reaching a stable plateau just at the time biochemical euthyroidism was obtained. These data suggest that osteoblastic activity is enhanced in hyperthyroidism and reduced in hypothyroidism, and that normalization occurs in close conjunction with the normalization of the thyroid state, without any delay, indicating a direct effect on the function of the excisting osteoblasts by the thyroid hormones. 相似文献
9.
The role of thyroid hormones in the regulation of adrenal function during stress has been documented in mammals, but only
limited reports are available in avian species. The present study was undertaken to analyze the effect of hyper- or hypothyroidism
on the adrenal activity under control (hydrated) and osmotically stressed (water deprived, WD) conditions, with special emphasis
on the expression of arginine vasotocin receptor VT2 (VT2R) in pituitary corticotrophs. Chickens were made hyper- or hypothyroidic
by injecting thyroxine (T4) and 2-thiouracil (TU), respectively for 14 days. After 10 days of injections, one sub-group of
both, T4- or TU-treated chickens were subjected to osmotic stress by water deprivation. Hyperthyroidism stimulated adrenal
steroidogenic activity compared to euthyroid control birds, but no change was observed in the expression of VT2R. On the other
hand, TU-induced hypothyroidism however showed no effect on adrenal gland, but a significant increase in the expression of
VT2R was observed. Neither hyper- nor hypothyroidism altered pro-opiomelanocortin (POMC) mRNA levels. Following osmotic stress,
no effect was observed either on the adrenal gland or on the VT2R expression in hyperthyroidic birds, but in hypothyroidic
birds, osmotic stress stimulated adrenal steroidogenic activity and decreased VT2R expression in comparison to its respective
controls (T4 or TU). Expression of POMC mRNA was again unaltered following osmotic stress. Although exact mechanism is not
clear, the data indicate that high plasma T4 level stimulates adrenal activity and may also modulate function of the pituitary–adrenal
axis during dehydration. 相似文献
10.
A new model has been used to evaluate the effects of thyroid hormones on brain development. This model is based on the assumption that the major effect of thyroid hormones is in regulating the rate of neurite growth of the rat brain at early stages of postnatal development. Microtubules were chosen as markers of neurite growth. We tested, therefore, whether the rate of microtubule assembly in vitro is under thyroid hormone control. The following results were obtained: The rate of tubulin assembly into microtubules in vitro seems to be thyroid hormone dependent: (a) in 15-day-old hypothyroid rats the rates of tubulin assembly in vitro are low, comparable to those levels found in normal rats on day 3; (b) normal rates of assembly in vitro are restored upon addition of very small amounts of microtubule fragments which act as nucleating centers in the process of microtubule formation; (c) addition of microtubule-associated proteins to a hypothyroid preparation restores maximal assembly rates; similar results were obtained on adding one of the microtubule-associated proteins (purified tau protein); (d) physiological amounts of thyroid hormones completely restore normal assembly rates provided that they are administered very early after birth; (e) the ability of tubulin to assemble maximally does not seem to be permanently impaired, since normal assembly rates are spontaneously restored when hypothyroidism is maintained until an adult stage; (f) normal microtubule assembly is observed when hypothyroidism is produced at an adult stage. The model which may be constructed from these results implies that thyroid hormones are required briefly after birth to accelerate the rate of microtubule assembly thus allowing intensive neurite growth during the critical period of brain development. 相似文献
11.
The hypothalamic-pituitary-thyroid axis plays a key role in skeletal development, acquisition of peak bone mass and regulation of adult bone turnover. Euthyroid status is essential for maintenance of optimal bone mineralization and strength. In population studies, hypothyroidism and hyperthyroidism have both been associated with an increased risk of fracture. Furthermore, recent studies in healthy euthyroid post-menopausal women indicate that thyroid status in the upper normal range is also associated with low bone mineral density and an increased risk of non-vertebral fracture. Studies in mutant mice have demonstrated that thyroid hormone receptor α is the major mediator of T3 action in bone and that thyroid hormones exert anabolic actions during growth but have catabolic effects on the adult skeleton. Nevertheless, TSH has also been proposed to be a direct negative regulator of bone turnover, although the relative importance of T3 and TSH actions in the skeleton has yet to be clarified. 相似文献
12.
妊娠期妇女体内激素水平会发生变化,使妊娠妇女甲状腺激素水平的测定和判断存在一定的困难,应选择适用于妊娠妇女的甲状腺激素水平特异值,进而正确评估甲状腺功能状态及对母体和胎儿的影响。孕前及妊娠期测定促甲状腺素和游离甲状腺激素有很大的必要性,因为甲状腺疾病以及单纯性甲状腺抗体阳性会导致多种妊娠不良结局,尤其是甲状腺功能减退对胎儿智力发育和认知功能具有非常大的影响。孕期甲状腺激素的监测对评估甲状腺功能状态及疾病预后具有非常大的作用,可以提示临床医师是否给予药物干预及如何调整药量。对于孕期甲状腺激素补充治疗后应达到的目标值以及甲状腺抗体阴性的亚临床甲状腺功能降低的妊娠患者是否给予干预,目前仍有异议。 相似文献
14.
The role of thyroid hormones in the development of the locomotor and cardiac muscles of the barnacle goose ( Branta leucopsis) was investigated. From 2 weeks of age, goslings were treated with thyroxine, triiodothyronine, or methimazole (a thyroid
inhibitor). Birds were killed at 6 weeks ( n = 5) or 9 weeks ( n = 4) and various locomotor and cardiac muscle masses recorded and tissue samples taken for analysis of citrate synthase activity.
The effects of thyroxine and triiodothyronine were not significantly different from each other, except in the case of the
iliofibularis at 9 weeks. The mass-specific citrate synthase activity of the iliofibularis, semimembranosus muscles and liver
were significantly increased by thyroid hormone treatment. Cardiac muscle showed a significant hypertrophy at 9 weeks of age
following treatment with thyroxine. Hypothyroidism induced by treatment with methimazole exhibited the greatest effect on
the pectoralis muscle, reducing citrate synthase activity by 33%. Mass-specific citrate synthase activity of the pectoralis
and pectoralis mass (% body wt.) were found to be highly correlated ( r
2 = 0.74) at 6 weeks of age. It is suggested that thyroid hormones may be involved in controlling the tissue-specific timing
of the maturation of locomotor and cardiac muscles.
Accepted: 16 September 1996 相似文献
15.
In birds, mothers can affect their offspring's phenotype and thereby survival via egg composition. It is not well known to what extent and time‐scales environmental variation in resource availability, either via resource constrains or adaptive adjustment to predicted rearing conditions, influences maternal effects. We experimentally studied whether egg and yolk mass and yolk hormone levels respond to short‐term changes in food availability during laying in wild great tits Parus major. Our treatment groups were: 1) food supplementation (mealworms) from the 1st until the last egg; 2) food supplementation from the 1st until the 5th egg, where the effect of cessation of the supplementary food treatment could also be studied; 3) no food supplementation (controls). We analysed both nutritional resources (egg, yolk and albumen mass), and the important developmental signals, yolk androgens (testosterone and androstenedione), and for the first time in a wild population, yolk thyroid hormones (thyroxine and 3,5,3′‐triiodothyronine). Egg mass is a costly resource for females, androgens most likely non‐costly signals, whereas thyroid hormones may be costly signals, requiring environmental iodine. In the food supplemented group egg, yolk and albumen mass increased rapidly relative to controls and when food supplementation was halted, egg and albumen mass decreased, indicating rapid responses to resource availability. Yolk androgen and thyroid hormone levels were not affected by food supplementation during laying. Thyroxine showed an increase over the laying sequence and its biological meaning needs further study. The rapid changes in egg mass to variation in within‐clutch food availability suggest energetic/protein/nutrient constrains on egg formation. The lack of a response in yolk hormones suggest that perhaps in this species the short‐term changes in resource availability during egg laying do not predict offspring rearing conditions, or (for thyroid hormones) do not cause systemic changes in circulating hormones, and hence do not affect maternal signaling. 相似文献
16.
We analysed barnacle Branta leucopsis and pink-footed goose Anser brachyrhynchus summer diets (May–July 2003) based on the proportions of different plant constituents in the faecal material of adult breeding
birds in Sassendalen, Svalbard to assess potential inter-specific competition. Diets were highly restricted and overlapped
little during pre-nesting and post hatch. During incubation both species showed greatest variety in their diet, reflecting
site-specific differences in local food abundance. However, locally the diets of pink-footed and barnacle geese resembled
each other most at this time (although still differing significantly). The conflicting needs of nest defence and maintenance
of body condition constrains the extent of the feeding resource utilised by nesting pairs and explains slightly greater dietary
overlap at this time. Hence, there is little evidence of inter-specific competition (interference or depletion) at present,
but this is most likely to be manifest during the incubation period in the future if goose numbers continue to increase. More
detailed investigations of the degree of spatial overlap of the two species and their effects on plant structure, quality
and community composition are necessary to predict likely outcomes of expected increases in numbers of both goose species. 相似文献
17.
It has been observed that basal and/or TRH-stimulated serum TSH levels occasionally conflict with the actual values of circulating thyroid hormones in patients with anorexia nervosa. In the present study sixteen female patients with anorexia nervosa during self-induced starvation displayed clinical findings suggesting hypothyroidism, e.g., cold intolerance, constipation, bradycardia, hypothermia and hypercholesterolemia in association with decreased serum total T3 (62.8 +/- 5.2 ng/dl) and T4 (6.6 +/- 0.3 micrograms/dl). Markedly decreased T3 correlated positively with average heart rate (r = 0.5655, P less than 0.025) and negatively with total cholesterol (r = -0.7413, P less than 0.005). This result may suggest that peripheral metabolic state of the underweight anorexics depends considerably upon the serum T3 concentration. Despite decreased total thyroid hormones, free T4 assayed by radioimmunoassay was normal in all five cases examined (1.4 +/- 0.2 ng/dl) and the free T4 index in fifteen cases was normal except in one case. Basal TSH was not increased and TSH response to exogenous TRH was not exaggerated in any. These results may be compatible with a theory that free T4 has a dominant influence on pituitary TSH secretion. Furthermore, glucocorticoids may also have some influence on depressed TSH response, because an inverse correlation between increased plasma cortisol and the sum of net TSH increase after TRH was observed in twelve cases examined. In conclusion, it is suggested that normal sensitivity of peripheral tissues and pituitary thyrotroph to different circulating thyroid hormones is maintained in anorexia nervosa patients even during severe self-induced starvation, and that the metabolic state in these patients is considerably under the influence of circulating T3. 相似文献
18.
Recently we reported that hyperglucagonemia induced by glucagon infusion causes a decline in serum T3 and a rise in reverse T3 in euthyroid healthy volunteers. These changes in T3 and rT3 levels were attributed to altered T4 metabolism in peripheral tissues. However, the contribution of altered release of thyroid hormones by the thyroid gland could not be excluded. Since the release of thyroid hormones is inhibited in primary hypothyroidism and is almost totally suppressed following L-thyroxine replacement therapy, we studied thyroid hormone levels for up to 6 hours after intravenous administration of glucagon in subjects with primary hypothyroidism who were rendered euthyroid by appropriate L-thyroxine replacement therapy for several years. A control study was conducted using normal saline infusion. Plasma glucose rose promptly following glucagon administration demonstrating its physiologic effect. Serum T4, Free T4, and T3 resin uptake were not altered during both studies. Glucagon infusion induced a significant decline in serum T3 (P less than 0.05) and a marked rise in rT3 (P less than 0.05) whereas saline administration caused no alterations in T3 or rT3 levels. Thus the changes in T3 and rT3 were significantly different during glucagon study when compared to saline infusion. (P less than 0.01 for both comparisons). Since, the release of thyroid hormones is suppressed by exogenous LT4 administration in these subjects; we conclude that changes in serum T3 and rT3 observed following glucagon administration reflect altered thyroid hormone metabolism in peripheral tissues and not altered release by the thyroid gland. 相似文献
19.
The data accumulated during the past twenty years suggest that thyroid hormones have a direct effect on the differentiation of both the neurons and the glial cell during the critical period of brain development. A fast survey of the available data (which is presented in the introduction of this article) on the mechanism of action of thyroid hormones and on their different effects during brain development suggests that the most dramatic effect of hypothyroidism is a hypoplastic neuropile. Both in vivo, during the critical period of nerve cell differentiation and in vitro, when added to primary cultures of embryonic nerve cells thyroid hormones stimulate neurite outgrowth. Since neurite outgrowth requires massive microtubule assembly the assumption was made that thyroid hormones stimulate nerve cell differentiation by changing the concentration and/or activity of the different proteins (tubulin and “microtubule associated proteins”, MAPs) which co-polymerize to form microtubules. Preliminary information was obtained by following the kinetics of microtubule assembly in crude brain supernatants. The data showed that: (1) the rate of in vitro microtubule assembly increases with age during brain development; (2) hypothyroidism, when produced in the rat at late pregnancy, slows this evolution; (3) early replacement therapy with thyroid hormones restores normal rates of assembly; (4) the addition of purified MAPs to normal young or 15-day-old hypothyroid brain preparations restores normal rates of polymerization. These and other data suggested that thyroid hormones regulate microtubule assembly by changing the concentration and/or activity of one or more of the MAPs. Further analysis revealed that striking qualitative changes in MAPs composition occur during brain development. For instance, the TAU fraction, a group of 4–5 proteins with a molecular weight of 60–68 K which is present in adult brain, is absent at early stages of postnatal development: two other entities are present, TAU slow and TAU fast, with different molecular weights, lower activity and different peptide mapping. This latter observation suggests that different TAU genes are expressed during brain development; a conclusion which has been confirmed by cell-free translation of the mRNas coding for these proteins. Analysis of the TAU fraction prepared from hypothyroid rat brains also revealed that a group of TAU proteins. “TAU3”, is almost missing, whereas thyroid hormone administration markedly increases its concentration. Two-dimensional gel electrophoresis showed that the TAU fraction is composed with more than 15 entities, with at least five of them being under thyroid hormone control. The precise physiological significance of the heterogeneity of MAPs and of the changes in MAPs composition seen during development and in hypothyroid rat brain remains to be determined. The assumption is made that these changes might be of utmost importance to regulate the number and length of the microtubules, and therefore the number and length of the neurites which are formed during the differentiation process of the different neurons. Thyroid hormones would be in these respects one of the epigenic factors required to synchronize sequentially the expression of the genes coding for these proteins in the different nerve cells. 相似文献
20.
The purpose of this investigation was to explore whether the pineal organ and its hormone melatonin has any influence on the activity of thyroid glands, if so, how that relates to the reproductive status of a hitherto unstudied seasonally breeding wild bird. Accordingly, an identical experimental regimen was followed with adult male spotted munia ( Lonchura punctulata; Passeriformes) during both its gametogenically active (August-September) and inactive (March-April) phases of the annual reproductive cycle. In either case, the levels of circulating thyroid hormones (both T 3 and T 4) and cellular characteristics of thyroid glands in groups of birds were studied following surgical removal of the pineal gland and/or daily afternoon administration of melatonin (10 μg/ 100 g body weight/ day for 30 days). The results of the same experimental schedule were found to be different depending on the sexual status of the concerned birds. During the breeding phase, pinealectomy (Px) induced significantly decreased values of T 3 and increased for T 4 along with hypertrophy of the thyroid follicular cells (TFC). The changes were reversed in melatonin treated Px birds. An increased amount of T 3 and decreased concentration of serum T 4 were also observed in melatonin injected intact birds. Conversely, the responses of TFC and of thyroid hormones in blood to either Px, or Px with melatonin, or to melatonin alone in intact munias during their inactive reproductive phase were just opposite to those noted during the breeding phase. The results of the present study suggest an influence of the pineal upon the thyroid in spotted munia. Moreover, it appears that this influence is carried out by melatonin, the action of which is reversible in relation with the gametogenic status of the concerned avian species. 相似文献
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