Avian muscular dystrophy: Thyroidal influence on pectoralis muscle growth and glucose-6-phosphate dehydrogenase activity

The pectoralis muscles of dystrophic chickens (line 413) were hypertrophic on the basis of fresh weight and fat-free dry weight. They also had greater DNA content and greater glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) activities. Of the parameters measured, the largest differences between pectoralis muscles from dystrophic and normal (line 412) chickens were for DNA content and G6PD activity. These parameters were 4.3- and 6.7-fold, respectively, the values for control pectoralis at 5 wk of age. The average number of nuclei per unit length of isolated muscle fiber was also greater (approximately 3-fold) for the dystrophic pectoralis. Body weight and pectoralis fresh weight, fat-free dry weight, DNA content, G6PD activity and 6PGD activity were reduced significantly in propylthiouracil (PTU)-treated normal and dystrophic chickens. Moreover, the effects of PTU were more pronounced in the dystrophic strain. Thyroid deprivation significantly improved the righting ability of the dystrophic chickens, in addition to its influence on muscle hypertrophy and body growth. Thyroxine (T₄) replacement reversed the PTU effects in both strains. Of all the variables measured, total G6PD activity was the most affected by PTU treatment of dystrophic chickens and was only 16% of the control dystrophic value.In addition to the effects of thyroid deprivation on the expression of avian muscular dystrophy, we observed significant differences in thyroid-related variables in the two strains. The average thyroid weight at 4 wk and serum triiodothyronine level at 5 wk for dystrophic chickens were 65 and 76%, respectively, of the normal values. The results that we report here indicate that altered thyroid function affects the expression of avian muscular dystrophy.     

Effects of thyroid state alterations in ovo on the plasma levels of thyroid hormones and on the populations of fibers in the plantaris muscle of male and female chickens.

Propylthiouracil (PTU), thyroxine (T4) or thyreoliberin (TRH) were injected in ovo to modify the thyroid state of chicken embryos. Significant sexual differences were observed in the effects of these treatments on the plasma concentrations of thyroid hormones and on plantaris muscle characteristics (DNA, RNA, populations of muscle fibers) in 3- and 35-day old male and female chickens. The T4 plasma concentration is lower in control males; it is decreased in PTU treated females and in the T4 treated females at 35 days. The T3 plasma concentration is lowered at 3 days in all treated chickens and also at 35 days in the TRH treated animals. The slow (STnO) and the fast (FTOG) fibers of the plantaris are always more numerous in males. In controls, the number of FTOG fibers remains steady between 3 and 35 days; at the same time, the number of STnO fibers rises in males only. Both PTU and T4 treatments increase the number of the FTOG and the STnO fibers respectively before and after the 3rd day. TRH treatment increases the number of STnO fibers at 3 and 35 days in males, but reduces it at 3 days in females. Thus changes in the number of FTOG fibers can be induced during in ovo myogenesis, whereas the number of STnO fibers may increase after hatching.     

Effects of thyroidectomy and administration of propylthiouracil (PTU) or thyrotropin (TSH) to pregnant rats on the functional development of the fetal thyroid gland an immunohistochemical study

In order to elucidate the maternal factors influencing the functional development of the fetal rat thyroid gland, pregnant rats were subjected to either thyroidectomy or administration of PTU or TSH and the thyroid glands of the fetuses were examined chronologically by immunohistochemistry to detect thyroglobulin (Tg), T4 and T3. In the group undergoing thyroidectomy, the occurrence of immunoreactive Tg, T4 and T3 was the same as in the control group in spite of slight retardation of the development of the thyroid gland. On the other hand, PTU administration caused remarkable degeneration of the hyperplastic epithelium of the follicles, where immunoreactivity of T4 and T3 was barely detectable, suggesting a transplacental effect of PTU on the fetal thyroid gland. However, Tg remained unaffected and was stained as well as in the controls. Injection of TSH led to a delay in the occurrence of T4 and T3 by one day, probably due to increased levels of thyroid hormone from the stimulated thyroid gland of the mother rats.     

Beneficial effects of anti-growth hormone antiserum in avian muscular dystrophy

Human subjects and mice have been found to have a milder progression of muscular dystrophy when the disease is associated with genotypically determined dwarfism. In this paper we describe an experimental test for reducing growth hormone in dystrophic chickens that uses rabbit anti-chicken growth hormone anti-serum (anti-cGH). Antiserum was injected daily into dystrophic (line 413) male chickens from day 1 to day 8 after hatching. Dystrophic chickens injected with anti-cGH maintained a significantly higher score in the standardized test for righting ability (P less than 0.001-0.051) from 3 to 9 1/2 wk after hatching when compared with dystrophic controls. The observed prolongation of the functional ability of injected dystrophic animals suggests that growth hormone plays a role in potentiating the symptoms of dystrophy in chickens.     

The effect of propylthiouracil and temperature on avian thyroid activity.

High ambient temperatures cause a reduction in thyroid gland size of chickens but propylthiouracil (PTU) treatment produces an increase in gland size regardless of temperature. This increase in size after PTU treatment during high temperature is evident after 7 days of PTU treatment but not after 14 days of treatment. Cyclic AMP-dependent protein kinase is activated in the thyroid gland with PTU treatment during high temperatures with no alteration in activity in the pituitary. These results suggest that the pituitary is not activated by TRH during periods of high ambient temperature and the thyrotrophs may release TSH in direct response to lowered serum thyroid levels produced by PTU treatment.     

Effects of noradrenaline, serotonin, and selected antagonists on the vascular smooth muscle of normal and dystrophic chickens

The pathogenesis of the human muscular dystrophies is unknown, and several competing hypotheses have been proposed. The vascular hypothesis states that muscle fibre necrosis occurs in dystrophy as a result of transient muscle ischemia. Although abnormalities of the vascular system may be demonstrated in dystrophy, their role in pathogenesis remains obscure. The responses to serotonin (5-HT) and noradrenaline (NA) were examined in isolated ischiatic artery preparations from normal and genetically dystrophic chickens. The tension generated in response to 5-HT was greater in arteries from normal chickens than in arteries from dystrophic chickens, whereas responses to NA were similar. Analysis of the concentration-response relationships demonstrated that the dystrophic ischiatic artery was less sensitive to 5-HT than was the normal artery, although the sensitivity to NA was similar in both vessels. The results of this study are not consistent with the view that muscle fibre necrosis in avian dystrophy is a consequence of muscle anoxia. These data do demonstrate pharmacological differences between dystrophic avian arteries and arteries from normal chickens, but their presence may represent merely the expression of dystrophy in vascular smooth muscle.     

Dietary thyrotropin-releasing hormone stimulates growth rate and increases the insulin: glucagon molar ratio of broiler chickens

The effects of thyroid manipulation on growth, feed efficiency, and plasma hormone levels were determined in rapidly growing chickens. Beginning at 3 weeks of age, eight broiler cockerels were provided with control feed (CF) or feed containing either 1 ppm of triiodothyronine (T3), 1 ppm of thyroxine (T4), 0.3% propylthiouracil (PTU), or 5 ppm of thyrotropin-releasing hormone (TRH) for 3 weeks. Blood samples were taken at 4, 5, and 6 weeks for determination of plasma levels of growth hormone, insulin-like growth factor, T3, T4, insulin, glucagon, glucose, and nonesterified fatty acids. Dietary TRH increased (P less than 0.05) the growth rate of chickens by 14% when compared with the CF group. Plasma growth hormone levels were reduced (P less than 0.05) 65% by dietary T3 and 33% by treatment with either T4 or TRH when compared with the CF group. Plasma insulin-like growth factor levels were 16% lower (P less than 0.05) in PTU-fed birds than the other treatment groups. Plasma T3 levels were elevated (P less than 0.05) 3-fold by dietary T3 and 38% by TRH whereas plasma T3 in the PTU group was 38% below the average of CF birds. Plasma T4 levels were increased (P less than 0.05) by 12-fold in T4-fed birds, decreased 48% in TRH-fed birds, and nondetectable in birds treated with either T3 or PTU. Compared with the other treatments, dietary PTU increased (P less than 0.01) plasma insulin levels 4.3-fold whereas TRH provided a 2.7-fold increase in plasma insulin. Plasma glucagon levels were 26% higher (P less than 0.05) in T3-fed birds than those fed either T4 or PTU. These observations indicate that thyroid activity plays an important role in regulating secretion of GH and the pancreatic hormones. Furthermore, our study demonstrates the potential use of TRH as an orally active growth promoter for poultry.     

Modulation of rat liver mitochondrial antioxidant defence system by thyroid hormone

In the present study the effect of thyroid hormone (T(3)) on oxidative stress parameters of mitochondria of rat liver is reported. Hypothyroidism is induced in male adult rats by giving 0.05% propylthiouracil (PTU) in drinking water for 30 days and in order to know the effect of thyroid hormone, PTU-treated rats were injected with 20 microg T(3)/100 g body weight/day for 3 days. The results of the present study indicate that administration of T(3) to hypothyroid (PTU-treated) rats resulted in significant augmentation of oxidative stress parameters such as thiobarbituric acid reactive substances and protein carbonyl content of mitochondria in comparison to its control and euthyroid rats. The hydrogen peroxide content of the mitochondria of liver increased in hypothyroid rats and was brought to a normal level by T(3) treatment. Induction of hypothyroidism by PTU treatment to rats also resulted in the augmentation of total and CN-sensitive superoxide dismutase (SOD) activities of the mitochondria, which was reduced when hypothyroid rats were challenged with T(3). Although CN-resistant SOD activity of the mitochondria remained unaltered in response to hypothyroidism induced by PTU treatment, its activity decreased when hypothyroid rats were injected with T(3). The catalase activity of the mitochondria decreased significantly by PTU treatment and was restored to normal when PTU-treated rats were given T(3). Total, Se-independent and Se-dependent glutathione peroxidase activities of the mitochondria were increased following PTU treatment and reduced when T(3) was administered to PTU-treated rats. The reduced and oxidised glutathione contents of the mitochondria of liver increased significantly in hypothyroid rats and their level was restored to normal when hypothyroid rats were injected with T(3). The results of the present study suggest that the mitochondrial antioxidant defence system is considerably influenced by the thyroid states of the body.     

Altered contents of tocopherols in chickens with inherited muscular dystrophy

Oxidative damage has been hypothesized as the basis for some of the changes in enzymatic functions and physical properties of membranes in inherited muscular dystrophy. The contents of alpha- and gamma-tocopherol (vitamin E) and their oxidation products, the tocopheryl quinones, were measured at 1 to 4 weeks after hatching in the muscle and other tissues of chickens with inherited muscular dystrophy. Analyses at these early ages minimized the potential influence of pathological changes on the measured parameters. The affected muscle (pectoralis major) of dystrophic birds contained significantly higher levels of alpha-tocopheryl quinone and a decreased ratio of alpha- to gamma-tocopherol. Consistent changes in these parameters were not observed in other tissues. Although their basis remains unclear, these changes in the tocopherols are suggestive of oxidative stress in dystrophic muscle membranes. Lipid extracts of tissues of normal and dystrophic birds exhibited no significant differences in the content of conjugated dienes or lipofuscins, two other indices of oxidative stress. These data do not consistently support the hypothesis that oxidative stress plays a causal role in damage to dystrophic muscle, although it remains possible that free-radical damage is involved in the secondary alterations associated with muscular dystrophy.     

Myofibrillar protein degradation in the chicken. 3-Methylhistidine release in vivo and in vitro in normal and genetically muscular-dystrophic chickens

Myofibrillar protein degradation was measured in 4-week-old normal (line 412) and genetically muscular-dystrophic (line 413) New Hampshire chickens by monitoring the rates of 3-methylhistidine excretion in vivo and in vitro. A method of perfusing breast and wing muscles was developed and the rate of 3-methylhistidine release in vitro was measured between 30 and 90min of perfusion. During this perfusion period, 3-methylhistidine release from the muscle preparation was linear, indicating that changes in 3-methylhistidine concentration of the perfusate were the result of myofibrillar protein degradation. Furthermore, the viability of the perfused muscle was maintained during this interval. After 60min of perfusion, ATP, ADP and creatine phosphate concentrations in pectoral muscle were similar to muscle freeze-clamped in vivo. Rates of glucose uptake and lactate production were constant during the perfusion. In dystrophic-muscle preparations, the rate of 3-methylhistidine release in vitro (nmol/h per g of dried muscle) was elevated 2-fold when compared with that in normal muscle. From these data the fractional degradation rates of myofibrillar protein in normal and dystrophic pectoral muscle were calculated to be 12 and 24% respectively. Daily 3-methylhistidine excretion (nmol/day per g body wt.) in vivo was elevated 1.35-fold in dystrophic chickens. Additional studies revealed that the anti-dystrophic drugs diphenylhydantoin and methylsergide, which improve righting ability of dystrophic chickens, did not alter 3-methylhistidine release in vitro. This result implies that changes in myofibrillar protein turnover are not the primary lesion in avian muscular dystrophy. From tissue amino acid analysis, the myofibrillar 3-methylhistidine content per g dry weight of muscle was similar in normal and dystrophic pectoral muscle. More than 96% of the 3-methylhistidine present in pectoral muscle was associated with the myofibrillar fraction. Dystrophic myofibrillar protein contained significantly less 3-methylhistidine (nmol/g of myofibrillar protein) than protein from normal muscle. This observation supports the hypothesis that there may be a block in the biochemical maturation and development of dystrophic muscle after hatching. Free 3-methylhistidine (nmol/g wet wt.) was elevated in dystrophic muscle, whereas blood 3-methylhistidine concentrations were similar in both lines. In summary, the increased myofibrillar protein catabolism demonstrated in dystrophic pectoral muscle correlates with the increased lysosomal cathepsin activity in this tissue as reported by others.     

Myogenic defect in muscular dystrophy of the chicken.

Inherited muscular dystrophy of the chicken is thought to arise from abnormal development of trophic regulation of skeletal muscles by their innervating nerves. To determine whether expression of muscular dystrophy in the chicken is a property of the nerves or of the muscles, wing limb buds were transplanted between normal and dystrophic chick embryos at $\text{3}\text{1}\text{2}$ days of incubation (stage 19–20). Muscles of donor limbs innervated by nerves of the hosts were compared to contralateral unoperated host limb muscles in chicks from 6 to 25 weeks after hatching. Expression of normal or dystrophic phenotype was determined by examination of five different properties which are altered in dystrophic chick muscle: electromyographic evidence of myotonia; fiber diameter; acetylcholinesterase activity, localization, and isozymes; lactic dehydrogenase activity; and succinic dehydrogenase activity. Genetically normal muscle innervated by nerves of normal or dystrophic hosts was phenotypically normal while genetically dystrophic muscle innervated by normal nerves was phenotypically dystrophic. The results suggest that inherited muscular dystrophy of the chicken arises from a defect of muscle rather than from a lesion in the nerves themselves.     

Thyroidal influence on body growth

This review of thyroid influence on body growth in poultry is organized around the following parameters of growth: increase in body weight and skeletal size, muscle growth, and growth of cartilage and bone. The greatest effect of goitrogens on growth of embryos occurs during late embryogenesis at a time when normal thyroid hormone levels are increasing. Posthatching growth is reduced in severely hypothyroid animals, and body weight gain is affected more than bone growth. Thyroid hormone replacement restores body growth of thyroidectomized chickens, but supplemental hormone in normal animals has no beneficial effect on growth. Excessive T3 (fed at 1 ppm) is detrimental to growth and feed efficiency. No clear correlation between thyroid hormone concentration and growth rate of normal chickens has been identified. Growth depression in sex-linked dwarf birds is at least partially reversed by supplemental T3. Muscle growth is reduced in goitrogen-treated chickens and the growth reduction is reversed by supplemental thyroxine. Total DNA accumulation is reduced in hypothyroid chickens, but muscle mass relative to DNA content is normal following long-term treatment; this suggests some regulation of muscle mass relative to DNA content. T3 increases the number of muscle fiber nuclei in hypothyroid chickens and the uptake of 3H-thymidine into nuclei within the basal lamina. T3 directly stimulates growth and maturation of embryonic chick cartilage and enhances the in vitro action of somatomedins on cartilage growth. There is little information concerning the role of the thyroid in posthatching cartilage and bone growth in poultry.     

Oxidation state of tissue thiol groups and content of protein carbonyl groups in chickens with inherited muscular dystrophy.

Indirect evidence suggests that oxidative stress may play a role in the pathogenesis of inherited muscular dystrophy, but the significance and precise extent of this contribution is poorly understood. Compared with normal muscle, significantly higher contents of glutathione, glutathione disulphide, protein-glutathione mixed disulphides and protein carbonyl groups, and significantly lower contents of free protein thiol groups, were found in pectoralis major muscle of genetically dystrophic chickens (the muscle affected by this disease) at 4 weeks of age. Other tissues did not show such marked disease-related differences. Interestingly, the protein pool in normal, but not dystrophic, pectoralis major muscle was relatively less oxidized in relation to the glutathione pool as compared with other tissues studied. The mechanisms by which this unique relationship between the thiol pools is maintained remain unknown. Although the physiological consequences of the increased content of protein carbonyl groups and the altered thiol pools in dystrophic muscle are not clear, the changes evident at such a young age are consistent with the occurrence of oxidative stress and may reflect significant damage to cellular proteins in this disease.     

The increase in hexokinase activity in hereditary avian muscular dystrophy.

Hexokinase activity was found to be increased in both the more severely affected red (thigh) muscle of dystrophic chickens. The increase in activity was largely associated with the particulate fraction. These findings may indicate early events in the pathogenesis of avian muscular dystrophy.     

Caffeine-modulated acetylcholine sensitivity in denervated rat and diseased human muscle.

Surgically denervated muscle exhibits increased sensitivity to acetylcholine and caffeine, and the acetylcholine contracture subsequent to preincubation with caffeine is greatly enhanced. The potentiation of the acetylcholine contracture derives, at least in part, from the direct action of caffeine on the muscle membrane resulting in an augmented and prolonged depolarization. The extent of potentiation depends on the duration of exposure to caffeine, is inhibited by increased extracellular calcium and is not present when cyclic AMP is substituted for caffeine.Biopsied human intercostal muscle shows high acetylcholine sensitivity in myotonic muscular dystrophy and motor neuron disease when compared to normal human or Duchenne dystrophic muscle. We suggest that myotonic dystrophy and motor neuron disease resemble surgical denervation more than Duchenne dystrophy does, and that in the former two diseases, as in denervated muscle, the acetylcholine sensitivity is increased with a concomitant abnormality in calcium-receptor interaction.     

Effects of the sex-linked dwarf gene (dw) on the expression of the muscular dystrophy gene (am) in chicken.

The sex-linked dwarf gene (dw) was introduced into companion muscular dystrophic (am) and nondystrophic (Am+) New Hampshire chicken lines to investigate influences of the dwarf gene on breast muscle weights, muscle fiber area, and the histological expression of muscular dystrophy. Dystrophic and nondystrophic chickens within dwarf or nondwarf genotypes were similar in body and carcass weights. Pectoralis and supracoracoideus muscle weights (as a percentage of adjusted carcass weight) were similar in nondystrophic dwarf and nondwarf males and females. In addition, pectoralis weight was similar in dystrophic dwarf males and dystrophic nondwarf males and females. However, pectoralis weight was significantly smaller in dystrophic dwarf females than in dystrophic nondwarf females, whereas supracoracoideus weight was significantly larger in dystrophic dwarf males than in dystrophic nondwarf males. Supracoracoideus weight was similar in dystrophic dwarf males and females and dystrophic nondwarf females. Pectoralis muscle fiber area was influenced by sex and by dwarf and dystrophy genotype. Muscle fiber area was larger in females than in males, smaller in dwarfs than in nondwarfs, and smaller in dystrophic than in nondystrophic muscles. Muscle fiber degeneration and adipose infiltration was more extensive in dystrophic than in nondystrophic females and males, and it was more advanced in dwarfs than in nondwarfs. Excessive acetylcholinesterase staining patterns were characteristic of dystrophic muscle in both dwarf and nondwarf genotypes. Nondystrophic and dystrophic dwarf male and female chickens are comparable substitutes for nondwarfs as biomedical models with respect to pectoralis histology, acetylcholinesterase staining pattern, and pectoralis muscle hypertrophy.     

Changes in the Levels and Forms of Cholinesterases in the Blood Plasma of Normal and Dystrophic Chickens

Abstract: Acetylcholinesterase (AChE) and pseudocholinesterase (°ChE) were analysed in the blood plasma of developing chickens, both normal and those with inherited muscular dystrophy. The amounts and the molecular forms of each were examined. °ChE concentration rises in the plasma of normal and dystrophic chicks at the end of embryonic development and is maintained after hatching at a constant, relatively high level, accounting for 90-95% of total cholinesterase activity in normal plasma. This level is maintained in normal and dystrophic chickens. In embryonic plasma of both normal and dystrophic chicks, on the other hand, the levels of AChE are higher than those of °ChE. Immediately after hatching the AChE level decreases rapidly in normal plasma, reaching a very low level by 2-3 weeks ex ovo. The AChE level in plasma from dystrophic birds, although less than normal from day 19 in ovo to 2 weeks ex ovo, subsequently increases to peak around 4 months at levels 15-20-fold of those in normal birds. There is virtually no enzyme of either type in the erythrocytes of normal or dystrophic chickens. The changes of AChE in plasma were correlated with the alterations of AChE in dystrophic fast-twitch muscles, suggesting that the latter pool is a precursor of the plasma AChE. Both the AChE and the °ChE in plasma exist in multiple molecular forms, which are similar to certain of those found previously in the muscles of these birds. The major form (60-80%) of both enzymes in the plasma is the M form (sedimentation coefficient ≥11 S) in all cases, but it is accompanied by certain other forms. In no case is there any of the heaviest form (H₂, 19-20 S) of AChE or of °ChE found in normal and dystrophic muscle, which is attached at the synapses in normal muscle. The pattern of forms of plasma °ChE is constant at all ages, and in normal and dystrophic chickens. The pattern of forms of AChE in the plasma, in contrast, varies with age and with dystrophy in a characteristic manner. The sedimentation coefficients and the amounts of the enzymes in fast-twitch muscle of dystrophic animals are compared with those of the plasma forms, and an interpretation is given of the characteristic patterns of AChE and of χE in their blood.     

Enzymological studies on hereditary avian muscular dystrophy.

White and red muscles of normal and genetically dystrophic chickens were compared with regards to activity levels of three soluble enzymes, glyceraldehyde-3-phosphate dehydrogenase, creatine phosphokinase, and acetyl phosphatase. In dystrophic white muscle (pectoral), activity of the two sulfhydryl enzymes, glyceraldehyde-3-phosphate dehydrogenase and creatine phosphokinase, was preferentially lost from the sarcoplasm resulting in decreased specific activities. By contrast, acetyl phosphatase was preferentially retained and showed increased specific activity. Dystrophic white muscle had decreased sulfhydryl content in the soluble proteins, severe reduction in muscle mass, fatty infiltration, and fragmentation of fibers. Red dystrophic muscles (thigh) were minimally involved in accordance with the known sparing of red fibers. Enzyme activities were correlated with histological observations. The results suggested that the disease process in dystrophic white muscle may be related to alterations in the sulfhydryl groups of proteins. The data are correlated with the beneficial effects of our treatment of hereditary avian dystrophy with the sulfhydryl compound, penicillamine (Chou, T.H., Hill, E.J., Bartle, E., Woolley, K., LeQuire, V., Olson, W., Roelofs, R., and Park, J.H. (1975) J. Clin. Invest. 56, 842-849).     

Phenothiourea sensitizes zebrafish cranial neural crest and extraocular muscle development to changes in retinoic acid and IGF signaling

1-Phenyl 2-thiourea (PTU) is a tyrosinase inhibitor commonly used to block pigmentation and aid visualization of zebrafish development. At the standard concentration of 0.003% (200 μM), PTU inhibits melanogenesis and reportedly has minimal other effects on zebrafish embryogenesis. We found that 0.003% PTU altered retinoic acid and insulin-like growth factor (IGF) regulation of neural crest and mesodermal components of craniofacial development. Reduction of retinoic acid synthesis by the pan-aldehyde dehydrogenase inhibitor diethylbenzaldehyde, only when combined with 0.003% PTU, resulted in extraocular muscle disorganization. PTU also decreased retinoic acid-induced teratogenic effects on pharyngeal arch and jaw cartilage despite morphologically normal appearing PTU-treated controls. Furthermore, 0.003% PTU in combination with inhibition of IGF signaling through either morpholino knockdown or pharmacologic inhibition of tyrosine kinase receptor phosphorylation, disrupted jaw development and extraocular muscle organization. PTU in and of itself inhibited neural crest development at higher concentrations (0.03%) and had the greatest inhibitory effect when added prior to 22 hours post fertilization (hpf). Addition of 0.003% PTU between 4 and 20 hpf decreased thyroxine (T4) in thyroid follicles in the nasopharynx of 96 hpf embryos. Treatment with exogenous triiodothyronine (T3) and T4 improved, but did not completely rescue, PTU-induced neural crest defects. Thus, PTU should be used with caution when studying zebrafish embryogenesis as it alters the threshold of different signaling pathways important during craniofacial development. The effects of PTU on neural crest development are partially caused by thyroid hormone signaling.     

Fiber-type-specific alphaB-crystallin distribution and its shifts with T(3) and PTU treatments in rat hindlimb muscles.

Changes in alphaB-crystallin content in adult rat soleus and extensor digitorum longus (EDL) were examined after 8 wk of 3,5, 3'-triiodothyronine (T(3)) and propylthiouracil (PTU) treatments. Cellular distributions of alphaB-crystallin expression related to fiber type, and distribution shifts with these treatments were also examined in detail from the gray level of reactivity to specific anti-alphaB-crystallin antibody. alphaB-crystallin content in both soleus and EDL muscles was significantly decreased after T(3), and that in EDL was significantly increased over twofold after PTU treatment. In both control soleus and EDL muscles, the gray level of type I fibers was higher than that of type II fibers. alphaB-crystallin expression among type II subtypes was muscle specific; the order was type I > IIa > IIx > IIb in control EDL muscle and type IIx > or = IIa in soleus muscle. The relation was basically unchanged in both muscles after T(3) treatment and was, in particular, well maintained in EDL muscle. Under hypothyroidism conditions with PTU, the mean alphaB-crystallin levels of type IIa and IIx fibers were significantly lower than levels under control conditions. Thus the relation between fiber type and the expression manner of stress protein alphaB-crystallin is muscle specific and also is well regulated under thyroid hormone, especially in fast EDL muscle.