Tubular transport processes in proximal tubules of hypothyroid rats. Lack of relationship between thyroidal dependent rise of isotonic fluid reabsorption and Na+−K+-ATPase activity

Hypothyroid rats reconstituted with 10 g/kg b.w. per day of tri-iodothironine (T₃) for 4 days resulted in normal free T₃ and TSH levels. FT₃ levels were: 0.53±0.3 pg/ml in hypothyroid rats; 2.78±1.21 pg/ml in hormone reconstituted rats and 2.90±0.90 pg/ml in euthyroid rats. TSH levels were 3,508±513 g/ml in hypothyroid rats; 1,008±204 g/ml in reconstituted rats and 270±184 ng/ml in euthyroid rats.When hypothyroid rats were reconstituted with 50 g T₃/kg b.w. per day, TSH levels were nearly normal after 4 days (1,157±621 ng/ml). However FT₃ levels after 1–4 days were always higher than in euthyroid rats.Hypothyroid rats show a decrease in isotonic fluid reabsorption (J _v) in the proximal tubule (1.50±0.08 versus 4.96±0.23 10^–2 nl·mm^–1·s^–1 in euthyroid animals). 1 day after T₃ (10 g/kg b.w./day) injectionJ _v was increased significantly to 2.05±0.20 10^–2 nl·mm^–1·s^–1 and continued to increase during 4 days of T₃ reconstitution.When 50 g T₃/kg b.w./day was used,J _v increased to 2.75±0.07 after 1 day and to 3.10±0.42 10^–2 nl·mm^–1·s^–1 after 4 days.J _v was never reaching a value close to that of euthyroid rats because the tubular radius in hypothyroid rats (14.7±1.8 m) is less than that of euthyroid rats (19.2±0.5 m). The radius in hypothyroid rats treated with T₃ was unchanged over a 4 day course with either high or low doses of T₃.Na⁺–K⁺-ATPase activity was found to be 2.91±0.16 M P_i/h×mg protein in homogenates of kidney cortex from hypothyroid rats. Treatment of hypothyroid rats with 10 g or 50 g of T₃ resulted in an initial decrease in ATPase activity, followed by an increase to base level in hypothyroid rats with 10 g and a significantly higher level with 50 g. This decrease in ATPase activity was contrasted to the increase inJ _v.These data indicate that there is a dissociation between the effects of physiological doses of thyroid hormones on proximal tubular reabsorption and the effects of T₃ on Na⁺–K⁺-ATPase activity of kidney cortex. This leads to question the relationship between sodium transport and ATPase activity under physiological doses of thyroid hormones. An early effect of physiological doses of thyroid hormones on brush border Na⁺ permeability is suggested.     

The effects of thyroid hormones on3H-ouabain binding site concentration,Na, K-contents and86Rb-efflux in rat skeletal muscle

Using a recently developed method based upon vanadate facilitated³H-ouabain binding, the total concentration of³H-ouabain binding sites was determined in biopsies of rat skeletal muscles containing varying proportions of slow-twitch fibres. In extensor digitorum longus, diaphragm, gastrocnemius and soleus muscles from mature (12-week-old) hyperthyroid rats the values obtained were respectively 2.6, 3.5, 5.1 and 9.8 times higher than those found in the same muscles from hypothyroid animals. This indicates that the effect of thyroid hormones is more pronounced on slow-twitch than on fast-twitch fibres. The changes in³H-ouabain binding site concentration with thyroid status could not be accounted for by differences in affinity or the rate of³H-ouabain binding.In young (4–5 week old) rats, where the K-content and the³H-ouabain binding site concentration in muscle had been reduced by K-depletion, T₃-pretreatment produced an even larger relative increase in the³H-ouabain binding site concentration than in age-matched controls, but no increase in K-content. Therefore, the downregulation of³H-ouabain binding sites seen during K-depletion cannot be attributed to a decreased response to thyroid hormones. In normal rats the marked stimulating effect of thyroid hormone on the synthesis of³H-ouabain binding sites was not associated with any significant change in K-content, but clearly preceded by a significant (P<0.001) rise in the efflux of⁸⁶Rb.     

Muscle and brown adipose tissue fatty acid profiles in cold-exposed rats

Effects of cold acclimation and cold exposure for 25 generations on triglyceride (TG)-, total phospholipid (PL)-, and cardiolipin (CL)-fatty acid (FA) compositions were studied in the different types of skeletal muscles (red and white muscles from quadriceps, and soleus) as well as brown adipose tissue (BAT) in rats. TG: in cold-acclimated rats (CA) and rats reared in cold for 25 generations (25G) white muscle showed the decreased saturated FA (SA) and increased polyunsaturated FA (PU). In soleus of 25G, monounsaturated FA (MU) and PU increased, and SA decreased. In BAT, SA increased and MU decreased in CA, and SA and PU decreased, and MU increased in 25G. PL: in red muscle of CA, SA increased and PU decreased. In red muscle of 25G the similar but more marked changes were found accompanied by lowered arachidonic acid and unsaturation index (UI). In BAT, SA, PU, arachidonic acid, and UI increased in CA, and arachidonic acid increased in 25G. CL: in red and white muscles of 25G, oleic acid and MU increased. In BAT, arachidonic acid increased in CA and 25G, and UI increased in 25G. These results suggest that FA unsaturation of CL in the muscles as well as BAT is involved in an enhanced thermogenesis in cold-exposed rats.     

Myocardial ultrastructure in cardiac hypertrophy induced by thyroid hormone—an acute study in rats

The early responses of the myocardium ultrastructure under thyroid dysfunction conditions, hemodynamic parameters, cardiac hypertrophy and ultrastructural evaluations were performed in hypothyroid and hyperthyroid rats submitted to different doses [T4–25 and T4–100; 0.025 mg and 0.1 mg kg^–1 body weight (BW) ·per day, respectively)]. All groups were treated for 7 days. The animals were sacrificed, the hearts were excised and weighed and the left ventricle tissue samples were processed for transmission election microscopy. Systolic blood pressure (SBP) was not altered by administration of T4. An increased heart rate and ratio of heart weight to body weight (HW/BW) were found in the hyperthyroid rats. However, the SBP and HW/BW decreased significantly in hypothyroid rats. No significant ultrastructural alterations were detected when the hypothyroid and T4–25 groups were compared with the control group. Alterations of cardiomyocytes nuclei of these groups were also not detected. Notably, disorganization of intercellular junctions was observed in many cardiomyocytes of T4–100 group. The present results indicate that in the early stages of hyperthyroidism, the cardiac hypertrophy development was mainly due to direct effects of thyroid hormone. Despite cardiac hypertrophy development, there is no ultrastructural evidence of myocardial degeneration.     

Effect of thyroid hormones and IGL in vivo on protein synthesis in the mitochondria of thyroidectomized animals

The effect of tri-iodothyronine (T₃) and IGL on the intensity of incorporation of L-[¹⁴C]tyrosine and on the rate of protein synthesis in the liver mitochondria of thyroidectomized rats and on the radioactivity of the amino-acid pool in the liver was investigated. The intensity of incorporation of L-[¹⁴C]tyrosine into proteins in the liver mitochondria of thyroidectomized animals and the rate of protein synthesis in them were found to be only half of their values in animals undergoing mock operations. Administration of T₃ or IGL to thyroidectomized rats restored protein synthesis in the liver mitochondria to normal. IGL had a similar effect to T₃ on all biochemical indices studied. The absence of thyroid hormones circulating in thyroidectomized animals or administration of T₃ or IGL to them did not change the radioactivity of the free tyrosine pool in the liver tissue.Central Biophysical Laboratory, Bulgarian Academy of Sciences, Sofia. (Presented by Academician of the Academy of Medical Sciences of the USSR N. A. Yudaev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 86, No. 8, pp. 167–170, August, 1978.     

Hypothyroidism in the rat results in decreased soleus motoneurone soma size

Adult female rats were thyroidectomized. After an average of 17 weeks, horseradish peroxidase (HRP) was injected into the right side soleus muscle. Two days later, left side soleus muscle properties were recorded and muscles and spinal cord were removed for further histological measurements. Soleus muscles from hypothyroid rats no longer contained type IIA fibers. Contraction and half-relaxation times of twitches had increased significantly compared to control rats. The average cross-sectional surface areas of HRP-labeled soleus motoneurones from hypothyroid rats were slightly but significantly smaller than those of control rats. A similar decrease in size was found for other (presumed moto-) neurones lying ventrolaterally to the soleus motor nucleus. It is concluded that changes in the soleus muscle fiber composition, as caused by lowered levels of thyroid hormone, are paralleled by corresponding changes in the size of its motoneurones and also of other spinal (moto)neurones.     

Energetic consequences of thyroid-modulated shifts in ventricular isomyosin distribution in the rat

Summary Heat production (measured myothermically), force development and isomyosin distribution were measured in left ventricular papillary muscles from adult male rats in three thyroid states: hyperthyroid (T₃), euthyroid (C) and hypothyroid (T_x). Rats were rendered hyperthyroid by daily injections of tri-iodothyronine and hypothyroid by radioisotopic thyroidectomy. Papillary muscle performance was measured both for trains of isometric twitches and for brief (2 s) tetani achieved by increasing the Ca²⁺ concentration and adding caffeine to the bathing solution. Resting metabolic rate was uninfluenced by thyroid state. Heat-stress relations were determined for both twitches and tetani by altering muscle length. T_x muscles showed an elevated stress-independent or activation heat (intercept of the heat-stress relation), a depressed stress-dependent heat (slope of the heat-stress relation), and greatly enhanced peak twitch and tetanic (S_max) stresses. When normalized for S_max, the maximal rates of tetanic stress development and heat production were depressed in the T_x group. In the T₃ group, only the normalized maximal rate of tetanic stress development was significantly increased. The lack of significant effects on other mechanical and energetic parameters probably reflects an under-dosing of animals in this tri-iodothyronine-treated group, an interpretation supported by the modest change in isomyosin distribution resulting from the treatment regimen used.Separate isomyosin analyses of papillary muscles and their associated ventricles yielded excellent correlation demonstrating the suitability of papillary muscles as a model of ventricular wall tissue. By experimentally manipulating the thyroid state, the distribution of the three ventricular isomyosins were correspondingly altered with a shift toward a greater and lesser proportion of high activity myosin ATPase in the hyperthyroid and hypothyroid groups respectively. The average proportions of the myosin heavy chain associated with high actin-activated myosin ATPase were 86, 74 and 6% for groups T₃, C and T_x respectively. The measured changes in papillary muscle energetics correlate well with these thyroid-induced changes in isomyosin distribution and can be explained in terms of altered crossbridge dynamics.     

Effect of altered thyroid state on the in situ mechanical properties of adult cat soleus

To determine the responsiveness of cat hindlimb muscles to thyroid manipulation, adult female cats were made hypothyroid (thyroidectomy plus tapazole treatment), hyperthyroid (synthroid pellets), or maintained euthyroid. After 4 months, the hypothyroid soleus had slower time-to-peak (TPT, 80%) and half-relaxation (HRT) times, whereas the hyperthyroid soleus had faster TPT (20%) and HRT than euthyroid cats. The tension at low stimulation frequencies (5-15 Hz) was higher in hypothyroid and lower in hyperthyroid cats compared to euthyroid cats. Muscle weight, maximum twitch and tetanic (Po) tensions, and maximum rates of shortening (Vmax) were similar across groups. The soleus of hypothyroid cats was more fatigable than normal. The myosin heavy chain (MHC) composition, based on gel electrophoresis, was unaffected by thyroid hormone manipulation. Based on the reaction of monoclonal antibodies for specific MHCs, some fast fibers in the hypothyroid cats coexpressed developmental MHC. These data indicate that 4 months of an altered thyroid state result in changes in the isometric twitch speed properties of the cat soleus, but not the tension-related or isotonic properties. Further, a chronic decrease in thyroid hormone had a greater impact than a chronic increase in thyroid hormone on the mechanical properties of the adult cat soleus.     

An Interaction Between Thyroid Hormone and Nerve Growth Factor Promotes the Development of Hippocampus,Olfactory Bulbs and Cerebellum: a Comparative Biochemical Study of Normal and Hypothyroid Rats

Abstract

The effects of treatment with L-thyroxine (T₄; 20 ng/g body weight, given subcutaneously on days 1, 3, 5, 7 and 9., 2.5 S nerve growth factor (NGF; 2 ngJmg brain wet weight, given intracerebroventricularly on days 1, 3, 5, 7 and 9), monoclonal anti-NGF (2 ng/mg wet weight, given intracerebroventricularly on days 1, 3, 5, 7 and 9), and monoclonal anti-NGF receptor (192 IgG; 2 ngJmg wet weight, injected daily from day 1 to day 9) antibodies, separately or together, were studied on the biochemical development of hippocampal formation, olfactory bulbs and cerebellum in 10-day-old and 15-day-old normal and hypothyroid rats. The results provide the following information: (1) CNS structures other than the basal fore-brain are sensitive to NGF during early development. (2) Both normal and hypothyroid rats are more sensitive to NGF deprivation than NGF supplementation. (3) The effects of anti-NGF antibodies in normal rats are similar to those induced by anti-NGFr antibodies. (4) NGF alone had little or no effect, but interacts with T₄ in promoting cell maturation, especially in hypothyroid rats. (5) Hypothyroid rats are more sensitive to T₄ and to T₄ plus NGF than are normal ones. (6) The synergistic action of both trophic factors, but not that of T₄, tend to disappear at long term in hypothyroid rats. (7) The differential sensitivity of the brain areas to T₄, NGF, or both trophic factors correlates with their cell acquisition rate, especially in hypothyroid rats. (8) T₄ and NGF together act more markedly (but not exclusively) on the cholinergic structures in both normal and hypothyroid rats. (9) RNA appears to be very sensitive to NGF, especially in hypothyroid rats. In close correlation with preliminary morphological observations, the results clearly demonstrate that an interaction between T₄ and NGF regulates the ontogeny of a number of neuronal structures in CNS independently of their neurotransmitter phenotype, but with a regional specificity. The possibilities of accounting for this interaction, in particular the major role of thyroxine, are discussed.     

Histology and immunocytochemistry of differentiated thyroid carcinomas do not predict radioiodine uptake: A clinicomorphological study of 62 recurrent or metastatic tumours

Summary Sixty-two metastases or recurrences of differentiated thyroid carcinomas were investigated using conventional histology and immunocytochemistry for thyroglobulin (TG), thyroxine (T₄) and triiodothyronine (T₃). In each patient,¹³¹I total body scans had been performed 4–10 weeks before surgery. Twenty-seven of the 62 tumours exhibited a predominance of follicles (A₁), while 35 either exclusively or predominantly consisted of papillae or, in the case of follicular carcinomas, were predominantly trabecular or solid in structure (A₂). TG and T₄ immunoreactivity was observed in 60 cases, only 4 of these also expressing T₃. Positive radioiodine uptake (RIU) was noted in 27 of 62 (44%) cases (A₁: 18/ 27=67%; A₂: 9/35=26%), 25 of which showed intraluminal TG and T₄ positivity. Two follicular carcinomas showing RIU lacked follicular lumina, but exhibited strong diffuse cytoplasmic positivity for both TG and T₄. In another 95 differentiated thyroid carcinomas, the structure of primary and secondary lesions was assessed. Of these, 27 (28%) showed a discordant pattern (A₁/A₂ or A₂/A₁) when comparing the structure of primary and secondary lesions. Our data suggest that differentiated thyroid carcinomas show a dissociation of TG/T₄ expression and RIU, defects of iodine uptake and storage being found more frequently than a depression of TG and T₄ synthesis. Intact synthesis of TG and T₄, but not of T₃ may be regarded as a prerequisite for RIU. Positive RIU is based on the presence of mature neoplastic follicles containing TG and T₄ immunoreactive colloid and among follicular carcinomas, positive RIU may be encountered in neoplasms lacking follicular lumina but exhibiting strong cytoplasmic TG and T₄ staining. Finally, the RIU of recurrent and metastatic PC and FC is not predictable from histological features of the primaries.Dedicated to Prof. Christoph Hedinger, former director of the Institute of Pathology, University of Zürich, on the occasion of his 75th birthday     

Effects of cold acclimation on cold-induced changes in lipid metabolism of rat brown adipose tissue.

Effects of acute cold exposure (0 degree C, 12 h) on lipid metabolism of the interscapular brown adipose tissue (BAT) were studied in warm controls (25 degrees C) (WC) and cold-acclimated rats (5 degrees C, 4 weeks) (CA). 1) We confirmed that cold acclimation brought about decreased BAT triglyceride (TG) level and increased BAT phospholipid (PL) level. The indexes of unsaturation, such as unsaturation index and polyunsaturated fatty acids/saturated fatty acids ratio, of bulky fatty acids (FA) (palmitic, stearic, oleic, and linoleic acids) decreased in TG, while those increased in PL. Rare FA (eicosadienoic acid, homo-gamma-linoleinic acid, lignoceric acid) level, which were about five times higher in PL than TG in WC, decreased in both TG and PL in CA. 2) Effect of acute cold exposure in WC: The level as well as the amount of TG in BAT was greatly reduced and the indexes of unsaturation in TG-FA increased. The most part of reduced TG (85%) was explained by the bulky FA. Rare FA explained only 1.1% of reduced TG. PL level in BAT did not change, but its amount decreased. The indexes of unsaturation increased in PL-FA. 3) Effect of acute cold exposure in CA: CA was placed in warm temperature of 25 degrees C before cold exposure. In contrast with the cold-reduced TG in WC, either the level or the total amount of TG in BAT did not change, but the indexes of unsaturation in TG-FA decreased. The level as well as the total amount of PL in BAT increased. The arachidonic index and arachidonate in PL-FA decreased, but the indexes of unsaturation did not change. These results indicate as a whole that acute cold exposure as well as cold acclimation influences BAT lipid metabolism in FA compositions as well as amount of TG and PL, suggesting that such changes are related to thermogenic activity of this tissue.     

Neutrophil responses to intravascular pneumococcal sonicate

Leukopenia and pulmonary leukostasis are prominent features in patients succumbing to pneumococcal (PNC) infections. We examined mechanisms involved in recruitment of polymorphonuclear neutrophils (PMNs) into pulmonary capillaries and alveolae after PNC sonicate injection. We showed that by 15 min postinjection, PMN chemotactic activity was found in bronchoalveolar lavage (BAL) fluids and increased with time until the end point of the study at 90 min. Accompanying the increased chemotactic activity in BAL fluids was a decrease in circulating PMNs more pronounced in the femoral artery (FA) then the pulmonary artery (PA). Super-oxide anion (O ₂ ^– ) production by peripheral PMNs was depressed following PNC sonicate injection, and comparison of FA and PA showed that FA PMNs produced less O ₂ ^– than PA PMNs. PA PMNs also showed enhanced random migration when compared to the depressed random migration of FA PMNs. This study demonstrated that an intravascular challenge of PNC sonicate was associated with increased chemotactic activity for PMNs in BAL fluid. Fewer PMNs and altered PMN function resulted from passage through the pulmonary microvasculature after PNC sonicate injection.Supported in part by USDHHS grant CA 20819 from the National Cancer Institute and from the Veterans Administration Research Service.     

Correlation between shortening velocity,force—velocity relation and histochemical fibre-type composition in rat muscles

Summary Isometric and isotonic contractions of three muscles in the rat hind leg (soleus, extensor digitorum longus (EDL) and peroneus longus (PL)) were recordedin situ at 35° C and with nerve stimulation. Additionally, the histochemical muscle fibre-type composition of the three muscles was determined by the method of Guth and Samaha (1970). The data obtained from soleus and EDL muscles were similar to those reported in previous studies. On the basis of twitch contraction time, rate of rise of tetanic tension and maximum shortening velocity, the contraction speed of EDL was 2–3 times higher than in soleus. In the PL muscle, the twitch contraction time, rate of tension rise and shortening velocity were 17 ms, 30Po/s and 12 muscle fibre lengths/s, respectively; the data showed that the contraction speed of PL muscle was intermediate between that of the soleus and EDL muscles. In the case of soleus, more than 75% of the cross-sectional area was occupied by type 1 (slow) fibres; in both EDL and PL muscles more than 90% of the area was occupied by type 2 (fast fibres). However, the two fast muscles (EDL and PL) had different proportions of type 2B fibres; the area occupied by the type 2B fibre complement was less than 5% in PL, whereas it was around 70% in EDL muscle. The differences in shortening velocity and force—velocity relation among the three muscles could be explained on the basis of their respective muscle fibre-type compositions.     

Potassium contractures and asymmetric charge movement in extensor digitorum longus and soleus muscles from thyrotoxic rats

Summary Potassium contractures and asymmetric charge movement were recorded from extensor digitorum longus (EDL) and soleus muscle from normal rats and rats that had been made thyrotoxic by daily intraperitoneal injections of triiodothyronine (150 g kg^–1) for two to three weeks. Potassium contracture tension (relative to tetanic tension) in thyrotoxic rats was greater in EDL muscles and smaller in soleus muscles than in normal rats. As the relationship between membrane potential and potassium concentration was unaltered by thyroid treatment, it was concluded that the changes in potassium contracture tension were due to changes in excitation-contraction coupling. In thyrotoxic rats there was an average negative shift of –5 mV in the voltage sensitivity of tension in EDL fibres and a positive shift of 5 mV in soleus. As a result, the tension-membrane potential curves for EDL and soleus fibres essentially coincided. There was a corresponding average negative shift of –4 mV in the voltage sensitivity of asymmetric charge in EDL fibres, and a positive shift of 4 mV in soleus fibres from thyrotoxic rats. The dependence of asymmetric charge movement on membrane potential became essentially the same in EDL and soleus fibres from thyrotoxic rats. The maximum asymmetric charge in soleus fibres increased from an average value of 6.5 nC F^–1 in normal rats (n=33) to 8.9 nC F^–1 in thyrotoxic rats (n=32;p<0.005). The increase in charge movement in EDL fibres in thyrotoxic rats was not statistically significant. The real increase was masked by an increase in linear capacity due to proliferation of T-system membrane: the density of triads where charge movement probably occurs did not increase.     

Thyroid hormone regulation of myosin heavy chain isoform composition in young and old rats,with special reference to IIX myosin

The effects of 4 weeks of thyroid hormone (3,5,3′-triiodothyronine, T₃) treatment on the myosin heavy chain (MHC) composition were compared in the slow-twitch soleus and the fast-twitch extensor digitorum longus (EDL) muscles from young (3–6 months) and old (20–24 months) male albino rats. Four MHC isoforms were separated on silverstained 6% sodium dodecyl sulphate polyacrylamide gel electrophoresis. According to immunoblotting experiments with specific MHC monoclonal antibodies, the four MHCs corresponded to types I, IIB, IIX and IIA. In the soleus, the type I MHC content was higher in the old than in the young animals, and the type IIA content lower. Type IIX myosin was observed in some young control soleus, but not in old ones. After T₃ treatment, the content of type I MHC decreased substantially in both young and old animals and that of type IIA increased. After T₃ treatment, type IIX myosin was observed in both young and old animals, with a slighty higher IIX myosin content in old age, but the age-related different in the contents of types I and IIA was diminished. In EDL, the type IIX MHC content was significantly higher in the old animals, at the significantly by T₃ treatment in EDL, either in young or old animals. In conclusion, an age-related motor unit transformation is observed in both the slow-twich soleus and the fast-twitch EDL and the capacity for MHC isoform switching in response to T₃ treatment is not impaired in old age.     

Thyroid hormone responsive protein (THRP) mediates thyroid hormone-induced cytotoxicity in primary neuronal cultures

The thyroid hormone responsive protein (THRP) is a novel gene product that remains responsive to thyroid hormone (TH) in the cerebral cortex of adult rats. To study the effects of THRP on neuronal cell survival, primary neurons cultured from rats at embryonic day 19 were treated with either 10^–7 mol L^–1 3,5,3-triiodothyronine (T₃), or 10^–7 mol L^–1 l-thyroxine (T₄). This resulted in decreasing neuronal cell number starting 48 h after treatment. T₃ -related cytotoxicity was also documented by measurement of lactate dehydrogenase release into the medium and by propidium iodide staining. Treatment of cells with 10^–7 mol L^–1 T₃ resulted in a significant increase in THRP mRNA levels as early as 24 h of treatment in a concentration-dependent manner. T₃ treatment did not alter glyceraldehyde 3-phosphate dehydrogenase (G3PDH) mRNA levels. Exogenous expression of THRP by transfecting cells with a THRP expression construct (pSVL-THRP) was associated with a significant increase in cell death as measured by the increased number of propidium iodide staining cells (18.0±2.1 cells per field) compared with mock-transfected cells (3.3±0.2), P<0.002. To further document THRP-induced cytotoxicity, the cells were either transfected with pSVL (empty vector)+pSV2neo (neomycin resistance vector for cell labeling), pSVL-THRP+pSV2neo, or pSVL-THRP+pc-Abl (cAbl tyrosine kinase expressing vector)+pSV2neo. After 24 h the cells were treated with 500 g mL^–1 G418 (a congener of neomycin) to eliminate the non-transfected cells. Transfection with pSVL-THRP reduced neuronal survival relative to cells transfected with pSVL (356±15.6 compared with 145±16.9, P<0.05). Co-transfection of THRP with wild-type c-Abl did not alter the effect of THRP on cell survival. It is concluded that THRP is an important factor in TH-induced neuronal cell death.     

Effect of hyperthyroidism on the contractile and histochemical properties of fast and slow twitch skeletal muscle in the rat

Male Wistar rats were made hyperthyroid by intraperitoneal injections on alternate days for 1–6 weeks, of 200 g/kg triiodothyronine (T₃). The effects of this treatment on the contractile properties of the soleus, a slow twitch and the extensor digitorum longus (EDL), a fast twitch skeletal muscle, were studied in vivo in the anaesthetized animal. Post mortem, serial frozen sections of both muscles were stained histochemically for myosin ATPase, succinic dehydrogenase and phosphorylase. Muscle fibres were classified as either slow twitch (SO), fast twitch oxidative glycolytic (FOG) or fast twitch glycolytic (FG).Elevation of plasma T₃ levels is associated with progressive alterations in the muscle fibre populations of both muscles. In the soleus there is conversion of SO to FOG fibres while in the EDL the main effect is FG to FOG conversion. There are also marked changes, mainly confined to the soleus muscle, in contractile properties; progressive increases in isometric twitch and tetanic tension and in the rates of contraction and relaxation during both twitch and tetanus.The effect of T₃ on slow muscle contractility may be related to its effect on muscle phenotype. However, changes in the former precede detectable fibre population changes. T₃ may influence properties such as the Ca²⁺ binding activity of sarcoplasmic reticulum of existing slow twitch fibres before the later changes associated with the interconversion of fibre types occur.     

The inflammatory response of hyperthyroid and hypothyroid rats. Role of adrenocortical steroids

The capacity to respond to inflammatory stimuli was tested in hyperthyroid and hypothyroid rats when thyroid defects, induced by hormone administration or thyroparathyroidectomy, respectively, were fully established. Whereas hyperthyroid rats presented consistently depressed inflammatory responses, hypothyroid rats responded in a normal fashion. Decreased reactions to intracutaneously injected histamine and serotonin, inhibited swelling reaction to carrageenin, injected into one of the hind paws, and depressed primary and secondary reactions to adjuvant (heat-killedM. tuberculosis), only occurred in the hyperthyroid group. In addition, only in this group of animals enlargement of the adrenal glands, reduced content of adrenal ascorbic acid, and decreased number of circulating eosinophils, which characterize a circumstance of adrenal cortical hyperactivity, were observed. A spontaneous reversal of the acute inflammatory response of hyperthyroid animals to carrageenin occurred 3–4 days after interruption of hormone administration, and this was coincidental with the return to normal of the previously enlarged adrenal glands. Similarly, specific inhibition of adrenal cortical steroid biosynthesis in hyperthyroid rats with amino-glutethimide, restored the previously depressed response to carrageenin, without interference with the increased levels of seric thyroxin, thus suggesting that the inhibitory effects of thyroid hormones on inflammatory responses are likely to be indirect. It is concluded that an excess of circulating thyroid hormones, but not their deficiency, can impair the development of inflammatory reactions, and that this effect, at least partially, depends on an increased secretion of adrenal corticosteroids.For correspondence.     

Collagen of slow twitch and fast twitch muscle fibres in different types of rat skeletal muscle

Summary The appearance of collagen around individual fast twitch (FT) and slow twitch (ST) muscle fibres was investigated in skeletal muscles with different contractile properties using endurance trained and untrained rats as experimental animals. The collagenous connective tissue was analyzed by measuring hydroxyproline biochemically and by staining collagenous material histochemically in M. soleus (MS), M. rectus femoris (MRF), and M. gastrocnemius (MG). The concentration of hydroxyproline in the ST fibres dissected from MS (2.72±0.35 g·mg^–1 d.w.) was significantly higher than that of the FT fibres dissected from MRF (1.52±0.33 g·mg^–1 d.w.). Similarly, the concentration of hydroxyproline was higher in ST (2.54±0.51 g·mg^–1 d.w.) than in FT fibres (1.60±0.43 g·mg^–1 d.w.), when the fibres were dissected from the same muscle, MG. Histochemical staining of collagenous material agreed with the biochemical evidence that MS and the slow twitch area of MG are more collagenous than MRF and the fast twitch area of MG both at the level of perimysium and endomysium. The variables were not affected by endurance training. When discussing the role of collagen in the function of skeletal muscle it is suggested that the different functional demands of different skeletal muscles are also reflected in the structure of intramuscular connective tissue, even at the level of endomysial collagen. It is supposed that the known differences in the elastic properties of fast tetanic muscle compared to slow tonic muscle as, e.g., the higher compliance of fast muscle could at least partly be explained in terms of the amount, type, and structure of intramuscular collagen.This study was supported by grants from the Finnish Research Council for Physical Education and Sport (Ministry of Education) and the Academy of Finnland     

Time course of the T3- and T4-induced increase in rat soleus muscle mitochondria.

Citrate synthase and cytochrome c increase in soleus muscle of rats in response to excess thyroid hormones. The half times of the increase in the levels of citrate synthase and cytochrome c in soleus muscle during induction are greater than the half times of the decline in enzyme levels after cessation of treatment (15 days vs. 7 days for citrate synthase). Denervation of the soleus does not prevent the increase in citrate synthase in response to thyrotoxicosis. This provides evidence that thyroid hormones affect the muscle directly and not via the motor nerves. ATP concentration is reduced in liver, but not in soleus muscle in response to thyrotoxicosis. Creatine phosphate is not significantly altered in soleus muscle. Cyclic AMP is slightly lower in thyrotoxic soleus muscle. Simultaneous treatment with thyroid hormones and propranolol does not affect the increase in citrate synthase in response to excess thyroid hormones. It is concluded that the increase in muscle mitochondria associated with thyrotoxicosis is not mediated via the nervous system or by a cAMP-regulated process.