Synergistic effect of aromatic plant essential oils on the ant Acromyrmex balzani (Hymenoptera: Formicidae) and antifungal activity on its symbiotic fungus Leucoagaricus gongylophorus (Agaricales: Agaricaceae)

Leaf-cutting ants have great potential for damage to agricultural and forest crops. Although chemical control is the most used method for the management of this pest, more friendly alternative methods have been investigated. Thus, this study aimed to evaluate the insecticidal and antifungal potential of essential oils obtained from Aristolochia trilobata, as well as the potential of two chemotypes of Myrcia lundiana and their major compounds (isopulegol and citral) on Acromyrmex balzani and its symbiotic fungus Leucoagaricus gongylophorus. Toxicity and synergism and/or antagonism tests were performed using essential oils and their major compounds on A. balzani ants. The antifungal activity of these compounds was tested on the fungus L. gongylophorus. The essential oils and their major compounds were toxic to A. balzani. The mixture of essential oils of A. trilobata with those of M. lundiana had higher toxicity to the ants. This synergistic effect is mainly due to the interactions between the citral compound and the major compounds present in A. trilobata essential oil. The essential oils of M. lundiana chemotypes showed antifungal properties against L. gongylophorus, and the citral compound proved to have fungicidal activity. These results show that the use of M. lundiana and A. trilobata essential oils and their major compounds is a potential alternative for the management of leaf-cutting ants A. balzani, as they have a toxic effect on worker ants and antifungal activity on their symbiotic fungus.

Ryanodine receptor point mutations confer diamide insecticide resistance in tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae)

Insect ryanodine receptors (RyR) are the molecular target-site for the recently introduced diamide insecticides. Diamides are particularly active on Lepidoptera pests, including tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae). High levels of diamide resistance were recently described in some European populations of T. absoluta, however, the mechanisms of resistance remained unknown. In this study the molecular basis of diamide resistance was investigated in a diamide resistant strain from Italy (IT-GELA-SD4), and additional resistant field populations collected in Greece, Spain and Brazil. The genetics of resistance was investigated by reciprocally crossing strain IT-GELA-SD4 with a susceptible strain and revealed an autosomal incompletely recessive mode of inheritance. To investigate the possible role of target-site mutations as known from diamondback moth (Plutella xylostella), we sequenced respective domains of the RyR gene of T. absoluta. Genotyping of individuals of IT-GELA-SD4 and field-collected strains showing different levels of diamide resistance revealed the presence of G4903E and I4746M RyR target-site mutations. These amino acid substitutions correspond to those recently described for diamide resistant diamondback moth, i.e. G4946E and I4790M. We also detected two novel mutations, G4903V and I4746T, in some of the resistant T. absoluta strains. Radioligand binding studies with thoracic membrane preparations of the IT-GELA-SD4 strain provided functional evidence that these mutations alter the affinity of the RyR to diamides. In combination with previous work on P. xylostella our study highlights the importance of position G4903 (G4946 in P. xylostella) of the insect RyR in defining sensitivity to diamides. The discovery of diamide resistance mutations in T. absoluta populations of diverse geographic origin has serious implications for the efficacy of diamides under applied conditions. The implementation of appropriate resistance management strategies is strongly advised to delay the further spread of resistance.

Field-Evolved Resistance and Cross-Resistance of Brazilian Tuta absoluta (Lepidoptera: Gelechiidae) Populations to Diamide Insecticides

Tuta absoluta (Meyrick), one of the most important tomato pests worldwide, is heavily controlled by the application of insecticides. Diamide insecticides represent a new class of products recently registered to control T. absoluta After 6 yr of use, control failures have been reported in populations of this pest, suggesting a hypothetical resistance development. Therefore, a resistance survey was performed using nine populations of T. absoluta that were collected in open fields, including from areas with reports of a reduced efficacy of diamides in the Northeast and Central regions of Brazil. Initial surveys with diagnostic and label doses proved the reduced efficacy of diamides against most populations. The LC₅₀ values of chlorantraniliprole varied from 0.0044 (Brasília) to 1,263 (América Dourada) mg AI liter^-1 (the resistance ratios [RR₅₀] ranged from 1.0- to 288,995-fold), whereas the LC₅₀ values for cyantraniliprole and flubendiamide, respectively, varied from 0.015 (Brasília) to 281 (América Dourada) mg AI liter^-1 and from 0.038 (Guaraciaba do Norte) to 3,018 (Gameleira 1) mg AI liter^-1 The resistance ratios (RR₅₀) ranged from 1.0- to 18,423-fold for cyantraniliprole and from 1.0- to 80,413-fold for flubendiamide. The log LC₅₀ values of pairwise diamides were strongly and significantly correlated, which denoted cross-resistance among them. Very high resistance to diamides in T. absoluta was observed in this study, suggesting that strategies to mitigate resistance and thereby control the pest must not include only insecticides. Other control tactics must be carefully implemented over time to increase the life span of diamides, including rotational practices with other molecules.

Stick-slip water penetration into capillaries coated with swelling hydrogel

We have observed intriguing stick-slip behavior during capillary pressure driven filling of borosilicate microtubes coated with hydrogel on their inner wall. Swelling of hydrogel upon exposure to a translating waterfront is accompanied by "stick-and-slip" motion. This results in the macroscopic filling velocity for water penetration into glass capillaries coated with poly(N-isopropylacrylamide) (PNIPAM) being constant throughout the filling process, and reduced by three orders of magnitude when compared to filling of uncoated capillaries. A simple scaling analysis is used to introduce a possible explanation by considering the mechanisms responsible for pinning and unpinning of the contact line. The explanation assumes that the time scale for water diffusion into a hydrogel film and the resulting swelling/change of the local meniscus contact angle define the duration of each "stick" event. The "slip" length scale is in turn established by the elastocapillary deformation of dry hydrogel at the pinning point of the contact line. The sequential dynamics of these processes then determine the rate of water filling into a swelling capillary. Collectively, these experimental and theoretical results provide a new conceptual framework for liquid motion confined by soft, dynamically evolving polymer interfaces, in which the system creates an energy barrier to further motion through elasto-capillary deformation, and then lowers the barrier through diffusive softening. This insight has implications for optimal design of microfluidic and lab-on-a-chip devices based on stimuli-responsive smart polymers.

Susceptibility of Tuta absoluta (Lepidoptera: Gelechiidae) Brazilian populations to ryanodine receptor modulators

BACKGROUND

Phthalic and anthranilic diamides comprise a new insecticide class recently registered in Brazil to control Lepidoptera such as Tuta absoluta (Meyrick). Therefore, the baseline of susceptibility was determined for eight representative field populations of this species to establish a resistance monitoring programme. The potential for cross-resistance as well as detoxification metabolism was assessed in order to fine-tune the resistance management programme.

RESULTS

Brazilian populations were very susceptible to chlorantraniliprole (LC50 values varied from 3.17 to 29.64 µg AI L(-1) ), cyantraniliprole (LC50 values varied from 8.61 to 28.95 µg AI L(-1) ) and flubendiamide (LC50 values varied from 94 to 230 µg AI L(-1) ), with respective resistance ratios of 9.33-, 3.36- and 2.45-fold between most susceptible and tolerant populations. Anthranilic diamides showed significant correlations between log LC50 values among themselves, suggesting a high risk of cross-resistance. However, the log LC50 values of T. absoluta to phthalic diamide did not show any correlation with anthranilic diamides. Cytochrome- P450-dependent monooxygenase activity showed a weak correlation with log LC50 values of T. absoluta populations to anthranilic diamides, which suggests a potential route for evolving resistance to anthranilic diamides.

CONCLUSION

The diamides were highly effective against T. absoluta, with populations showing a homogeneous response to them. Cross-resistance is very likely between anthranilic diamides in T. absoluta. Populations of this pest may evolve resistance by increasing cytochrome- P450-dependent monooxygenases.

Metabolic and neuroendocrine responses to Roux-en-Y gastric bypass. I: energy balance, metabolic changes, and fat loss

CONTEXT

Obesity is a major health problem. Effective treatment requires understanding the homeostatic responses to caloric restriction.

OBJECTIVE

The aim was to study Roux-en-Y gastric bypass patients longitudinally for 6 months after surgery to identify major factors modulating fat loss.

METHODS

We studied 13 patients (11 females and two males) aged 41.2 ± 2 yr. Mean body mass index was 44.6 ± 1.2 kg/m(2), with 50 ± 1% body fat (58.3 kg). Selection excluded patients with confounding comorbidities or treatments.

RESULTS

Caloric intake was reduced 742 ± 82 kcal/d by 1 month and 450 kcal/d between 2 and 4 months postoperatively. By 6 months, relative to baseline, body mass index decreased 24.8 ± 1.1%; percentage body fat, 37.3 ± 3.2% (21.7 kg); fat free mass (FFM), 9.7 ± 1.2%; and resting metabolic rate (RMR), 18.1 ± 4.3%. RMR correlated with FFM at all times (r = 0.71; P < 0.0001), but FFM explained no more than 50% of RMR variance. Exercise capacity (treadmill walking, 53 m/min with increasing grade) improved with time. Mean nonexercise physical activity level was low (1.2, or 20% of RMR), with considerable variance among individuals. Fat loss did not correlate with the aggregate energy deficit or its individual components. Resting or postexercise respiratory exchange ratio (RER) was lowest, whereas plasma β-OH-butyrate and glycerol were highest, between 1 and 2 months after surgery. RER increased linearly with mild exercise, and fat loss correlated positively with physical activity level and RER.

CONCLUSIONS

Although the ultimate cause for weight loss is the energy deficit, the variance in fat loss correlated with glucose oxidation, suggesting that glucose partition between oxidation (muscle) and storage (adipose tissue) is an important factor affecting fat loss in individuals submitted to Roux-en-Y gastric bypass.

Type-2 iodothyronine 5'deiodinase (D2) in skeletal muscle of C57Bl/6 mice. II. Evidence for a role of D2 in the hypermetabolism of thyroid hormone receptor alpha-deficient mice

Mice with ablation of the Thra gene have cold intolerance due to an as yet undefined defect in the activation of brown adipose tissue (BAT) uncoupling protein (UCP). They develop an alternate form of facultative thermogenesis, activated at temperatures below thermoneutrality and associated with hypermetabolism and reduced sensitivity to diet-induced obesity. A consistent finding in Thra-0/0 mice is increased type-2 iodothyronine deiodinase (D2) mRNA in skeletal muscle and other tissues. With an improved assay to measure D2 activity, we show here that this enzyme activity is increased in proportion to the mRNA and as a function of the ambient cold. The activation is mediated by the sympathetic nervous system in Thra-0/0, as it is in wild-type genotype mice, but the sympathetic nervous system effect is greater in Thra-0/0 mice. Using D2-ablated mice (Dio2-/-), we reported elsewhere and show here that, in spite of sharing a severe deficiency in BAT thermogenesis with Thra-0/0 and UCP1-knockout mice, they do not have an increase in oxygen consumption, and they gain more weight than wild-type controls when fed a high-fat diet. UCP3 mRNA is highly responsive to thyroid hormone, and it is increased in Thra-0/0 mice, particularly when fed high-fat diets. We show here that muscle UCP3 mRNA in hypothyroid Thra-0/0 mice is responsive to small dose-short regimens of T(4), indicating a role for locally, D2-generated T(3). Lastly, we show that bile acids stimulate not only BAT but also muscle D2 activity, and this is associated with stimulation of muscle UCP3 mRNA expression provided T(4) is present. These observations strongly support the concept that enhanced D2 activity in Thra-0/0 plays a critical role in their alternate form of facultative thermogenesis, stimulating increased fat oxidation by increasing local T(3) generation in skeletal muscle.

Type-2 iodothyronine 5'deiodinase in skeletal muscle of C57BL/6 mice. I. Identity, subcellular localization, and characterization

RT-PCR shows that mouse skeletal muscle contains type-2 iodothyronine deiodinase (D2) mRNA. However, the D2 activity has been hard to measure. Except for newborn mice, muscle homogenates have no detectable activity. However, we have reported D2 activity in mouse muscle microsomes. As the mRNA, activity is higher in slow- than in fast-twitch muscle. We addressed here the major problems in measuring D2 activity in muscle by: homogenizing muscle in high salt to improve yield of membranous structures; separating postmitochondrial supernatant between 38 and 50% sucrose, to eliminate lighter membranes lacking D2; washing these with 0.1 M Na(2)CO(3) to eliminate additional contaminating proteins; pretreating all buffers with Chelex, to eliminate catalytic metals; and eliminating the EDTA from the assay, as this can bind iron that enhances dithiothreitol oxidation and promotes peroxidation reactions. Maximum velocity of T(3) generation by postgradient microsomes from red muscles was approximately 1100 fmol/(h · mg) protein with a Michaelis-Menten constant for T(4) of 1.5 nM. D2-specific activity of Na(2)CO(3)-washed microsomes was 6-10 times higher. The enrichment in D2 activity increased in parallel with the capacity of microsomes to load (sarco/endoplasmic reticulum Ca(2+)-ATPase) and bind Ca(2+) (calsequestrin), indicating that D2 resides in the inner sarcoplasmic reticulum, close to the nuclei. The presence of D3 in the sarcolemma suggests that the most of D2-generated T(3) acts locally. Estimates from maximum velocity, Michaelis-Menten constant, and muscle T(4) content suggest that mouse red, type-1, aerobic mouse muscle fibers can generate physiologically relevant amounts of T(3) and, further, that muscle D2 plays an important role in thyroid hormone-dependent muscle thermogenesis.

Leaching behaviour of a galvanic sludge in sulphuric acid and ammoniacal media

Leaching studies of a sludge produced by the physico-chemical treatment of wastewaters generated by a Ni/Cr plating plant were carried out in both sulphuric acid and ammoniacal media aiming to decide which of them would be the best treatment for this kind of waste material. The dissolution behaviour of some metals (Cu, Ni, Cr and Zn) was studied in order to assure the best metal recovery conditions in subsequent processes by the use of some separation methods such as solvent extraction and precipitation techniques. Therefore, the study here presented deals with the first chemical stage of an integrated treatment process. For the sulphuric acid leaching, maximal conversions obtained were 88.6% Cu, 98.0% Ni and 99.2% Zn for the following experimental conditions: a 100 g L(-1) acid concentration, a 5:1 liquid-to-solid ratio (L/S), a particle size less than 1 mm, a digestion time of 1h, a stirring speed of 700 rpm (all at room temperature and under atmospheric pressure). As expected, no selectivity was achieved for the sulphuric acid leaching, despite this option yielding much higher metal ion dissolution when compared with that reached by ammoniacal leaching. The use of this latter medium allowed the extraction of Cu and Ni without Cr species, but rates of conversion were only about 70% for Cu and 50% for Ni, much lower than those obtained for sulphuric acid leaching.

Solvent extraction applied to the recovery of heavy metals from galvanic sludge

In this study, a hydrometallurgical treatment involving the solvent extraction and recovery of some heavy metals from a sulphuric acid leach solution of galvanic sludge, using di-(2-ethylhexyl)-phosphoric acid (D2EHPA) and bis-(2,4,4-trimethylpentyl)-phosphinic acid (Cyanex 272), both diluted in kerosene, has been investigated. The preliminary tests revealed the necessity to remove other metal species than zinc and nickel, contained in the leach solution, and therefore, processes to cement copper and precipitate chromium were then applied to finally obtain a Zn and Ni pregnant solution prior to solvent extraction. For the experimental conditions studied, Cyanex 272 showed a good recovery of Zn after the stripping stage using H2SO4, but D2EHPA effectively promoted a higher Zn extraction than Cyanex 272 did. The dependence of the solvent extraction method on variables such as pH, contact time and concentration of extractant, as well as the effect of different concentrations of sulphuric acid on stripping, are discussed. The discussion also includes the previous conditions developed to separate the main interfering metallic species from the leach solution in order to improve the extraction and recovery of zinc by solvent extraction. The final objective has been to achieve a solution as pure as possible to recover nickel sulphate.

Role of the mixing conditions and composition of galvanic sludges on the inertization process in clay-based ceramics

Hydroxide-metal sludges from electroplating industry are a potential source of environmental contamination due to their high content of heavy metals. The incorporation of these residues in a ceramic matrix can be a promising way to suppress the harmful effect of metals normally present in those sludges. This work reports the role of the mixing time between the waste and ceramic materials and of the calcination step on the fixing level of several metal-containing species (Al, Zn, Ni, Fe, Ca, Cu, Cr) after sequential leaching in different media (aqueous, acetate and citrate). A strong and/or long mixing process will promote the deagglomeration of the coarser agglomerates and then will increase the reactivity of remaining grains towards the ceramic material during the calcination. As a consequence, inertization is improved for fired samples. With non-calcined samples leaching increases as a result of increasing dispersability/availability of species.

Effect of experimental variables on the inertization of galvanic sludges in clay-based ceramics

The incorporation of several industrial wastes in ceramic matrixes had been attempted as an effective low expense technique for the fixation of metallic species in usable products or simply to reduce the residue volume for further disposal. However, the dominant mechanism of the inertization process and the relevant influent parameters are still unknown, mostly due to the complexity of the systems. This work reports the effect of several processing parameters such as the mixing time, the calcination temperature and duration, the relative amount of sludge, and the physical aspect of the sample (powdered or pressed pellets) on the fixing level of relevant species (SiO2), SO4(2)-, Zn, Ni, Ca, Cu, Cr) by leaching in different media (aqueous, acetate, and citrate). Statistical tools were used to define the relevance of each experimental variable on the inertization process of the used galvanic sludge. The relative amount of sludge in the mixture, the calcination temperature and the agglomeration state of the sample were found to be the most influent parameters of the inertization process. The incipient reaction between sludge and ceramic matrix components points out for the dominance of a macro-encapsulation mechanism.

Thiazolidinediones inhibit the expression of beta3-adrenergic receptors at a transcriptional level

The effect of the thiazolidinediones (TZDs) darglitazone and troglitazone on beta3-adrenergic receptor (AR) expression was studied in cultured cell lines representing several tissues. After 24 h of exposing HIB-1B brown adipocytes to 30 micromol/l darglitazone or 20 micromol/l troglitazone, beta3-AR mRNA levels were reduced by 75%. This effect was significant within 1 h of exposure to a maximal dose of these drugs, with the full effect obtained within 10 h. The darglitazone ID50 was approximately 10 nmol/l, similar to the Kd of TZDs binding to peroxisome proliferator-activated receptor-gamma (PPAR-gamma). These drugs also decreased beta3-AR mRNA in 3T3-F442A white adipocytes, but not in SK-N-MC cells, which lack PPAR-gamma2. A luciferase reporter gene containing 1.4 kb of 5' flanking sequence of the mouse beta3-AR was transiently transfected, with or without PPAR-gamma2, in SK-N-MC cells. The vigorous expression of luciferase driven by the beta3-AR gene sequence was inhibited by TZDs in a PPAR-gamma2-dependent manner. The half-lives of gamma3-AR precursor RNA and mRNA were short, approximately 40 and approximately 100 min, respectively, and remained unaffected by TZD treatment. Exposure of HIB-1B cells to 30 micromol/l darglitazone was associated with reduced beta3-AR mRNA levels, as well as decreased response of uncoupling protein 1 to norepinephrine + propranolol (a beta1 beta2-AR antagonist) or the specific beta3-AR agonist CL 316, 243. Both the beta3-AR mRNA level and response to these stimuli fully recovered by 24 h of removing the drug, indicating that the beta3-AR protein and its coupling to adenylyl cyclase rapidly followed the changes in mRNA. Thus, TZDs can rapidly reduce beta3-AR expression at the transcriptional level, acting through PPAR-gamma2. The rapid turnover and responses of beta3-AR to perturbations, along with numerous other factors reported to regulate its expression, suggest a tight control of beta3-AR and function. Lastly, leptin being the only other known gene suppressed by TZDs, the present studies support a concerted lipogenic effect of these drugs.

Glucocorticoids inhibit the transcriptional response of the uncoupling protein-1 gene to adrenergic stimulation in a brown adipose cell line

Glucocorticoids may inhibit brown adipose tissue (BAT) thermogenesis acting at a central level as well as reducing the responses of the tissue to adrenergic stimulation in vivo. This latter effect is not well understood. We investigated whether or not glucocorticoids directly reduce the expression of the key molecule for BAT thermogenesis, uncoupling protein-1 (UCP1), and if so, to what extent and by what mechanisms. We used HIB-1B brown adipose cells obtained from a hibernoma. The response of UCP1 mRNA to adrenergic stimulation in these cells is qualitatively and quantitatively similar to that seen in vivo. Dexamethasone and other glucocorticoids, given simultaneously with NE, nearly abolish the ensuing UCP1 mRNA accumulation. This effect was negated by the glucocorticoid receptor antagonist RU-486. Significant inhibition is seen within the physiological range of concentrations, with ID(50)s for dexamethasone and corticosterone of 1 and 75 nM, respectively. Within the time span of the experiments, glucocorticoids did not reduce the strength of the NE signal nor did they necessitate ongoing protein synthesis or reduce the stability of mature UCP1 mRNA, but they significantly inhibited the stimulation of transcription by NE in a run-on in vitro transcription assay. These observations indicate that glucocorticoids are powerful inhibitors of the UCP1 gene response to adrenergic stimulation acting at transcriptional level, and provide further evidence for a global inhibitory effect of glucocorticoids on BAT thermogenesis.

Uncoupling protein-2 and -3 messenger ribonucleic acids in adipose tissue and skeletal muscle of healthy males: variability, factors affecting expression, and relation to measures of metabolic rate

Mitochondrial uncoupling protein-2 and -3 (UCP2 and UCP3) may be involved in the modulation of resting metabolic rate and energy balance. To investigate their variability, the influence of this on the variability of energy expenditure, and potential regulatory factors of the expression of the corresponding genes, we measured their messenger ribonucleic acids (mRNAs) in muscle and white adipose tissue of lean, healthy men and correlated the abundance of these mRNAs (attomoles per microg total RNA) with measures of resting metabolic rate, hormone levels (thyroid hormones, insulin, glucagon, leptin, and catecholamines), and fuels potentially involved in energy balance regulation. We also investigated whether the thiazolidinedione, troglitazone, stimulates UCP2 and UCP3 mRNA levels to follow up on the observation that this antidiabetic drug increases the levels of expression in cultured cells. We found UCP2 and UCP3 mRNA levels to be highly variable and poorly correlated with measures of energy expenditure and with most factors affecting energy balance. Only nocturnal urinary norepinephrine excretion could explain a significant fraction of the variability in both UCP2 and UCP3 expression in muscle, but not adipose tissue. Thyroid hormone and norepinephrine excretion were found to contribute to the variability of resting metabolic rate, but this could not be explained by an effect on UCP mRNAs. Troglitazone affected neither the expression of UCPs nor the hormones or the measures of metabolic rate investigated. In conclusion, our results show that the expression of UCP2 and UCP3 genes is quite variable in healthy males and that this variability does not explain that in resting energy expenditure, and suggest that sympathetic activity is an important potential regulator of the expression of these proteins in skeletal muscle. However, the data do not support the concept that regulation of the expression of these genes is the most important level of control of UCP3 and UCP2 functions, and other levels of control have to be invoked.

Frequency of suspected cases of neurocysticercosis detected by computed skull tomography in Santa Maria, RS, Brazil

Due to the lack of studies about neurocysticercosis in the South of Brazil, an investigation was conducted to determine the percentage of suspected cases of neurocysticercosis in computed tomography diagnoses in Santa Maria, RS, from January 1997 to December 1998. Of 6300 computed tomographies (CT) of the skull performed at the private Hospital de Caridade Astrogildo de Azevedo, 80, i.e., 1.27% were suspected of neurocysticercosis. Fifty were women (62.5%) and 30 were men (37.5%). The most frequent radiological manifestation indicating neurocysticercosis was the presence of calcifications (isolated or associated), with a 95% rate (76 cases), while the presence of hypodense lesions reached a 5% rate (4 cases). After routine analysis, each CT was evaluated again and the suspected cases were confirmed. The percentage of suspected cases of neurocysticercosis detected by CT in the present study carried out in Santa Maria was considered low (1.27%). This can be explained by the fact that tomography is not accessible to the economically underprivileged population of Santa Maria. We hope that the present study can alert the population and the professionals to the fact that neurocysticercosis is a more frequent disease than indicated by the few diagnoses made.

The physiological role of the novel uncoupling proteins: view from the chair

The recently cloned uncoupling proteins -2 and -3 (UCP2, UCP3) cDNAs encode for proteins with 57-59% homology with brown adipose tissue uncoupling protein (UCP1) that can function as uncouplers of phosphorylation. The presentations of this Session of the Symposium were largely based on mRNA measurements, with one study showing that protein concentrations are well predicted by changes in mRNA in human muscles. Overall the observations suggest more complexity than anticipated. These observations are for the moment hard to reconcile with a simple role for these proteins in energy dissipation. Just the marked differences in tissue distribution of the two novel UCPs suggest they have different functions. It is possible that the activity, rather than the concentrations of these proteins, is regulated. The investigation of this possibility will hopefully enlighten us on their physiological role.

[Importance of J. Brazy's neurobiological index. Prediction of the number and severity of complications in very low birth weight infants]

The objective of this study was to evaluate the neurodevelopment outcome of Very-Low-Birth-Weight Infants (VLBW), between 1987 and 1993, and correlate these findings with J.Brazy's Neurobiologic Risk Score (NBRS). The minimum corrected age at follow-up was 12 months. The neurodevelopmental assessment was performed using Mary Sheridan and Ruth Griffiths scales, Auditory and Visual Brainstem Evoked Responses and Stycar test. The NBRS was applied to 77 children. According to the score, three groups of risk were defined: Low < or = 4; Intermediate 5-7; High > or = 8. We obtained the following results: children with NBRS < 4, 20% had handicaps (5% of which major); children with NBRS 5-7, 41% had handicaps (23% of which major); in children with NBRS > 8, 95% had handicaps (80% of which major). The incidence of handicaps, (all grades included) was 71.4% for those weighing less than 1000 gr at birth, and 39.2% for those weighing 1000-1499 gr at birth. Major handicaps, mainly motor deficits, occurred in 26.8% of VLBW infants and minor to moderate handicaps were observed in 18.3% of patients in this group. These results were compared to J.Brazy's originals. We concluded that the NBRS, which is simple and objective to perform, is a good predictor of subsquent abnormal development in VLBW infants, allowing the infant's integration as soon as possible in high-risk follow-up programs, to place as soon as possible.

Calcium pool size modulates the sensitivity of the ryanodine receptor channel and calcium-dependent ATPase of heavy sarcoplasmic reticulum to extravesicular free calcium concentration

We have examined calcium cycling and associated ATP consumption by isolated heavy sarcoplasmic reticulum (HSR) vesicles incubated in conditions believed to exist in resting muscle. Our goals were to estimate the magnitude of calcium cycling under those conditions and identify the main mechanisms involved in its regulation. The integrity of the HSR vesicles was documented by the retention of [14C]-sucrose and electron microscopy. HSR actively exchanged Ca2+ with the medium through a partially open ryanodine-binding channel (RyR), as evidenced by the rapid attainment of a steady-state gradient between HSR and medium, which was promptly increased by the closure of the channel with ruthenium red (RR) or collapsed by its opening with caffeine. The ATP dependency was evidenced by the sustained ATP consumption after the steady state was attained and by the abrogation of the gradient following inhibition of the pump with thapsigargin (Tg) or the omission of ATP. When HSR vesicles were incubated in a comparatively large pool of calcium (approximately 1 micromol/mg HSR protein), ATP consumption was 1-1.5 micromol x [min x mg protein](-1) at 0.1 microM free Ca2+. Under such conditions, the main regulator of the sarcoplasmic Ca2+-dependent ATPase (SERCA) was extravesicular-free Ca2+ concentration, with a four- to fivefold increase between 0.1 and 2 microM Ca2+, whereas RyR channel activity and the replenishment of the HSR vesicles had only a modest effect on ATP consumption. When calcium pool size was reduced to 0.1 micromol/mg HSR protein, a steady state was established at a lower level of HSR calcium. In spite of a slightly lower free extravesicular Ca2+ at equilibrium (approximately 0.07 microM following an initial concentration of 0.1 microM), both ATP consumption and the open probability of the RyR channel were increased by a factor of three to five. Compared to the large calcium pool, the sensitivity of both RyR channel and SERCA to extravesicular free Ca2+ concentration as well as to caffeine and RR was markedly enhanced.

CONCLUSIONS

1) In conditions present in resting muscle, HSR calcium is in dynamic equilibrium with the medium through a partially open RyR channel, which requires continuous ATP hydrolysis. 2) The availability of calcium is a major determinant of the sensitivity of both RyR channel and SERCA to free extravesicular Ca2+ and possibly other stimuli. 3) These observations are consistent with the concept that calcium cycling in resting muscle may account for a significant fraction of muscle energy demands and further suggest that restricting calcium availability may enhance the energetic demands of this process.

Thiazolidinediones stimulate uncoupling protein-2 expression in cell lines representing white and brown adipose tissues and skeletal muscle

Thiazolidinediones (TZD) are PPAR gamma ligands that sensitize tissues to insulin. A cDNA encoding a mitochondrial protein likely to act as uncoupler (uncoupling protein 2, UCP2) has been recently cloned. Since TZD have been reported to increase energy expenditure in animals, we have examined the effects of these drugs on the expression of UCP2 mRNA in cell lines representing white (3T3-L1 and 3T3-F442A) and brown (HIB-1B) adipose tissues and skeletal muscle (L6). Northern blots probed with a mouse UCP2 full-length cDNA showed a mRNA of 1.6 kb both in tissues and the aforementioned cells lines. Within 4 h of exposing these cells to 30 microM darglitazone, there was an increase in UCP2 mRNA which reached a plateau of 5-10 times the basal in about 8 h. In all cells TZDs (darglitazone, troglitazone) were more active than the predominantly PPAR alpha ligands WY-14,613 and clofibrate, or the non-selective ligand linoleic acid. These results indicate that TZDs can stimulate the expression of UCP2 gene probably via PPAR gamma and hence have the potential to increase energy expenditure in adult humans, in whom UCP2 is expressed ubiquitously.

3',5'-cyclic adenosine monophosphate-response sequences of the uncoupling protein gene are sequentially recruited during darglitazone-induced brown adipocyte differentiation

Uncoupling protein-1 (UCP) is uniquely expressed in brown adipose tissue (BAT) and is essential to the thermogenic function of this tissue. The UCP gene is under the control of norepinephrine (NE) via cAMP. However, the precise delineation of the cAMP response sequences and mechanisms whereby cAMP stimulate the gene have remained elusive. A BAT tumor cell line, HIB-1B, can be differentiated into UCP-expressing brown adipocytes. We report here that when these cells are differentiated with a standard differentiation protocol including insulin, T3, hydrocortisone, IBMX, and indomethacin (standard differentiation, StD), cAMP stimulation of the rat UCP gene is largely mediated by an upstream 90-bp sequence -2,399/-2,490 (R90) with a lesser contribution of a downstream sequence -57/+114 (dnCRS). This latter is functional also in non-BAT cells, whereas the cAMP response sequence contained in R90 (upCRS) is BAT-specific. Thiazolidinediones (TZD) are a new group of drugs known to increase sensitivity to insulin and, more recently, to induce adipocyte differentiation (adipogenesis) via PPARgamma. A TZD, darglitazone (darg), can rapidly induce differentiation of HIB-1B cells, as judged by the expression of the adipocyte lipid binding protein (aP2), lipoprotein lipase (LPL), uncoupling protein (UCP) and beta3-adrenergic receptors. UCP messenger RNA (mRNA) responsive to NE is evidenced as early as one day after exposure to darg. While UCP-CAT vectors (+114/-3673 bp of rat UCP gene) are barely responsive to NE in HIB-1B preadipocytes, both darg and StD markedly enhance NE responsiveness of such constructs. However, by 3 days of exposure to darg, the responses were less vigorous than in StD cells (4- to 10-fold vs. 20- to 50-fold), and the deletion of R90 did not affect the response to NE in darg-differentiated cells, whereas this deletion caused a 75% reduction in StD cells. Prolongation of darg exposure to 5-7 days resulted in greater response of UCP mRNA to NE and 50-80% inhibition of the response of UCP-CAT vectors by the deletion of R90. Thus, darg-induced differentiation of HIB-1B cells suggests that the NE-dependent expression of the UCP gene takes place in a step-wise manner: first, the gene is "enabled," as no UCP mRNA is detected in HIB-1B preadipocytes; thereafter and transiently, the response of the gene to NE is sustained by dnCRS; finally, as differentiation progresses, a cell-specific and more powerful cis-acting sequence, upCRS, is recruited, accounting in the fully differentiated cell for most of the response to NE. These results also suggest that TZDs might increase energy expenditure by inducing terminal differentiation of BAT, and that these drugs may be useful in the differential cloning of the factors involved in the recruitment of the BAT specific cAMP response sequence.

Resting energy expenditure is sensitive to small dose changes in patients on chronic thyroid hormone replacement

We have investigated the effects of modifying the dose of thyroxine on resting energy expenditure (REE) and on the thermic effect of glucose (TEG) in 9 randomly recruited patients on chronic treatment with this hormone. The initial dose was changed twice in each patient at 6-8 wk intervals, aiming to have a normal, a slightly reduced, and a slightly elevated serum TSH concentration. A total of 27 dose points for each measured variable (3 per patient) were gathered. Dose changes were monitored with serum free T4, T3, and TSH. At the end of each dose period, low density lipoprotein and high density lipoprotein cholesterol, triglycerides, angiotensin converting enzyme, and sex hormone binding globulin were also measured, along with a systematic assessment of symptoms and signs. The investigators involved in the measurements were blinded to the dose of T4. Serum free T4 and TSH significantly correlated to the dose in each patient and in the whole group, whereas serum T3 levels were minimally affected by the dose and did not correlate with it, with free T4 or with TSH. This latter was below normal on 9 occasions, normal in 12, and above normal in 6. Serum free T4 and T3 remained within the normal range on all except 2 occasions. REE and TEG were normalized to fat-free mass (FFM). In each patient there was a significant negative correlation between REE and TSH. This correlation was maintained when all data were pooled (r2 = 0.64; P < 0.001). Also, initial REE and its change between the highest and the lowest thyroxine dose were significantly correlated with, respectively, initial serum TSH (r2 = 0.85; P < 0.001) and the change in serum TSH between the highest and the lowest dose of T4 (r2 = 0.67; P < 0.0065). REE decreased approximately 15% when TSH increased between 0.1 and 10 mU/L. In 6 of the 9 patients, TEG increased with the reduction of the dose, and higher values were associated with higher TSH levels but without reaching statistical significance (F = 2.852, P = 0.077). None of the other indices were significantly affected by the changes in dose. These results indicate that, in patients on chronic treatment with thyroxine, REE is significantly influenced by the dose of this hormone in a dose range encompassing serum TSH concentrations that are considered acceptable in the management of hypothyroid patients. In the absence of physiological or behavioral compensations, these changes in REE may be clinically relevant.

Regulation of the uncoupling protein gene expression

Uncoupling protein (UCP) is essential to the thermogenic function of brown adipose tissue (BAT). The thermogenic role of this protein is due to its capacity to uncouple oxidative phosphorylation in a regulated manner. The thermogenic potential of BAT is determined by its content of UCP. The gene encoding this protein is under complex regulation. Catecholamines, via cAMP, thyroid hormone and retinoic acid, directly stimulate the gene acting upon an upstream (-2.28/-2.49 kb) enhancer sequence, but cAMP may act upon other sequences of the gene as well. CCAAT enhancer binding proteins and peroxisome proliferation activator receptor (PPAR) gamma 2 have also been implicated in the regulation of the gene acting on discrete sequences. While the thyroid hormone response and retinoic acid response elements (TRE and RARE) have been well defined, the cAMP response elements (CRE) remain elusive. The two TREs are 27 bp apart between -2.33 kb and -2.39 kb. The synergism between cAMP and thyroid hormone seems to reside in a 39 bp sequence downstream (-2.28/-2.32 kb). The most important CRE, the RARE, a cell-specific enhancer and a putative PPAR element are all concentrated in a 90 bp regulatory element of great complexity (-2.40/-2.49 kb). Other hormones, such as insulin and glucocorticoids, and IGF-I also modulate the expression of the gene but their effects seem to be largely indirect. Understanding the regulation of the UCP gene expression may facilitate the development of interventions in obesity and related disorders.

Rainbow trout liver expresses two iodothyronine phenolic ring deiodinase pathways with the characteristics of mammalian types I and II 5'-deiodinases

Deiodinases are major determinants of thyroid hormone tissue availability and disposal. The knowledge of the expression of these enzymes in lower species is important to understand evolutionary and ontogenetic aspects of thyroid hormone action and metabolism. Here we have studied outer ring deiodination in the trout liver using both reverse T3 (rT3) and T4 as substrates. The use of rT3 disclosed two enzymatic components with the characteristics of mammalian types I and II 5'-deiodinases. The high rT3-K(m) type I 5'-deiodinase activity (180 nM) has a low cofactor requirement (5 mM dithiothreitol) and is relatively sensitive to propylthiouracil inhibition, whereas the low rT3-K(m) activity was akin to the outer ring deiodination of T4 in these regards. The use of T4 exhibited only a single type of activity with a low K(m) (0.63 nM), a relatively high cofactor requirement (25 mM dithiothreitol), and propylthiouracil-resistance. Teleosts constitute a unique example of type II activity expression in the liver of an adult vertebrate. Furthermore, the Vmax of this enzyme is as high as that found in comparable homogenates from hypothyroid mammalian tissues, whereas the Vmax of the type I activity is lower than that of mammalian liver. These findings are in consonance with the peculiar kinetics of T3 in trout liver, kinetics remarkably similar to those of the mammalian pituitary, cerebral cortex, and brown adipose tissue, which also preferentially express type II deiodinase.

Effects of hypothyroidism on brown adipose tissue adenylyl cyclase activity

Hypothyroidism profoundly reduces the capacity of brown adipose tissue (BAT) to generate cAMP in response to adrenergic stimulation. Evidence obtained with isolated brown adipocytes suggests a postreceptor defect that offsets the hypothyroidism-induced increase in beta3-adrenergic receptors. The goal of the present studies was to identify the defect in the cAMP generation pathway for which we studied cAMP generation in isolated cells and purified BAT membranes from normal and hypothyroid rats. Studies with adenosine deaminase and the adenosine receptor-1 agonist r-phenyl isopropyl adenosine (R-PIA) show that hypothyroid cells are not more sensitive to adenosine (same EC50) but more inhibited by high concentrations of R-PIA. Pretreatment with pertussis toxin reduced the gap in cAMP generation between eu- and hypothyroid cells and the inhibition mediated by R-PIA, but did not normalize the cAMP response to forskolin in hypothyroid cells. Although purified euthyroid BAT membranes increased cAMP production with GTP concentrations up to submillimolar range, to plateau or slightly decrease at higher levels, hypothyroid membranes were weakly stimulated by low concentrations of GTP and markedly inhibited (>50%) at concentrations > or = 10(-4) M. When assayed at 0.3 mM ATP and 1 microM GTP, hypothyroid membranes actually generated more cAMP in response to forskolin, but this was reversed when GTP concentration was 1 mM. Immunoblotting studies showed no significant effects of hypothyroidism on the abundance of G(alpha)i or Gbeta subunits, and ADP ribosylation of G(alpha)i was only 45% increased in hypothyroidism in contrast to a 2.5-fold increase in hypothyroid white adipose tissue membranes from the same rats. Hypothyroid membranes also exhibited different kinetics regarding ATP, with higher cAMP generation at submillimolar concentrations but less at >1 mM ATP. Actually, at ATP concentrations >0.6 mM, cAMP generation was markedly inhibited in hypothyroid membranes. Fixing the concentration of free Mg++ in these experiments indicates that most of the inhibition seen in hypothyroid membranes is caused by ATP, whereas euthyroid membranes are more sensitive to changes in free Mg++. Ca++ +/- calmodulin did not stimulate adenylyl cyclase (AC) activity. On the contrary, AC activity was inhibited by Ca++ in a concentration-dependent manner, by as low as 100 nM free Ca++, and to greater extent in hypo- than in euthyroid membranes (maximal inhibition 60 vs. 25-30%). Our results suggest that, functionally, hypothyroidism causes a change in the AC of BAT membranes consistent with a relative or absolute increase in the type VI AC (AC-VI). The effects on this AC of nucleotides, Ca++, and Mg++ at concentrations prevailing in the hypothyroid brown adipocyte are probably the major factor in the reduced capacity of these cells to generate cAMP. These results also open the possibility of a novel, differential effect of thyroid hormone on AC expression, and support the concept that thyroid hormone affects the adrenergic signal transduction pathways in a tissue-selective manner.

Amplification of the parathyroid hormone-related peptide gene in a colonic carcinoma

PTH-related peptide (PTHrP) is the major factor responsible for humoral hypercalcemia of malignancy. This paraneoplastic syndrome has been described in association with a number of malignancies, but rarely with carcinoma of the colon. Moreover, little is known about the molecular mechanisms that underlie PTHrP overexpression in tumors. Here we report a patient who presented with hypercalcemia 6 months after resection of a neuroendocrine colonic carcinoma (tumor I). At the time of admission, intact PTH was decreased, circulating PTHrP levels were elevated, and there was tumor recurrence (tumor II). Immunohistochemical staining of paraffin-embedded sections from tumor I did not stain for PTHrP, whereas cells from tumor II stained intensely positive. Southern blot analysis and differential PCR of genomic DNAs from tumor specimens and the patient's leukocytes demonstrated amplification of the PTHrP gene in tumor II. Moreover, staining for p53 protein was evident in tumor II, but not in tumor I, consistent with the presence of a mutant form of p53 and associated loss of tumor suppressor function in the recurrent tumor. PTHrP gene amplification was also detected in one of five other tumors associated with humoral hypercalcemia of malignancy. These findings suggest that a potential mechanism contributing to PTHrP overexpression in malignancies is gene amplification, which could arise from increased genomic instability associated with the progressive stages of neoplasia.

Interactions among receptors, thyroid hormone response elements, and ligands in the regulation of the rat uncoupling protein gene expression by thyroid hormone

Uncoupling protein (UCP) is essential to the thermogenic function of brown adipose tissue (BAT). Thyroid hormone stimulates the rat UCP gene through two thyroid hormone response elements (TRE) located upstream of -2,300 and separated by 27 bp. They are an everted repeat (upstream TRE or upTRE) and a direct repeat (down-stream TRE or dnTRE). The goal of the present studies was to investigate whether these TREs interact and how such an interaction could contribute to explain the UCP responsiveness to T3 in vivo. We therefore aimed to define: the heterodimeric partner of the T3 receptor (T3R); the role of T3 in the receptor-receptor and receptors-DNA interactions; how such in vitro interactions relate to the enhancer function of TREs; and how the two TREs interact. Studies included electrophoretic mobility shift assays, utilizing T3R and retinoid X receptors (RXR); DNA footprinting; and transient transfections of HIB-1B cells, a BAT-derived cell line. As in many previously described TREs, the partner of the T3R is RXR. The unliganded T3Rs bind to the TREs as homodimers, which act as repressors of transcription. T3 reduces the binding of T3R homodimers, hence relieving the repression, and stimulates the binding of heterodimers and transcription in proportion to the heterodimer binding to the elements. Although qualitatively similar in these regards, there were important quantitative differences between both TREs. The upTRE binds more T3R homodimers and less T3R-RXR heterodimers than the dnTRE, and T3 more readily facilitates heterodimer binding to the dn- than to the upTRE. These in vitro characteristics are reflected in a lower efficiency of T3 to relieve T3R homodimer-mediated repression and to stimulate transcription through up-than through dnTRE. There were also significant interactions between the two TREs both in the binding of the receptors, T3R and RXR, and in the responsiveness to T3. By itself, each TRE responded modestly to T3, upTRE with lower sensitivity and dnTRE with higher sensitivity than traditional TREs, whereas together, in the context of the gene sequence, they mediated a response greater than the sum of those mediated by each TRE separately, with an intermediate sensitivity to T3. Thus, two TREs that are inadequate to explain the responsiveness of the UCP gene to T3, together form a complex unit appropriate for the regulation of the gene by thyroid hormone. These interactions represent yet another way TREs can shape up the responsiveness of genes to thyroid hormone.

A complex retinoic acid response element in the uncoupling protein gene defines a novel role for retinoids in thermogenesis

Retinoids have been implicated in the control of cell proliferation and differentiation, and in several developmental processes. We report here the molecular bases for a metabolic role of RA, by showing that the expression of the uncoupling protein (UCP), the key element in brown adipose tissue (BAT) thermogenesis, is stimulated by retinoic acid (RA). Both all-trans-RA and 9-cis-RA powerfully increase UCP messenger RNA levels in isolated rat brown adipocytes. Transient transfection experiments in HIB-1B cells, a BAT-derived cell line, identified the sequence -2399/-2490 (called R90) as the RA-responsive sequence in the rat UCP gene. R90 mediated a 20- to 70-fold stimulation of the chloramphenicol acetyl transferase reporter gene by maximal concentrations of all-trans-RA or 9-cis-RA. Non-BAT cells were significantly less responsive. RA effect was also less when chloramphenicol acetyl transferase gene was driven by a heterologous promoter instead of the UCP minimal promoter. By footprinting and site-directed mutagenesis, we identified three discrete sequences as being essential for the RA response within R90, thus defining the complex RA response element (RARE) of this gene. Critical bases in these sequences are arranged in pairs of putative half-sites. RAR gamma-RXR heterodimers can bind to the R90 as revealed by electrophoretic mobility shift assays using in vitro translated receptors, and HIB-1B nuclear extracts with anti-RAR gamma or anti-RXR antibodies. The participation of RAR gamma-RXR heterodimers in RA stimulation is further supported by transient transfection experiments overexpressing selected receptors and dose-response analyses of RA isomers and analogues. These results show that retinoids strongly stimulate the rat UCP gene expression through a complex RARE, composed of three pairs of half-sites, and define a novel role for retinoids in the regulation of facultative thermogenesis and energy expenditure.

Thyroid hormone control of thermogenesis and energy balance

The mechanisms whereby thyroid hormone increases heat production have been analyzed with emphasis in more recent developments. Thyroid hormone increases obligatory thermogenesis as a result of the stimulation of numerous metabolic pathways involved in development, remodeling, and delivery of energy to the tissues. In addition, thyroid hormone may specifically stimulate some thermogenic mechanisms selected during evolution of homeotherms (e.g., Na/K-ATPase, Ca2+ cycling in muscle). Thyroid hormone also plays an essential role in facultative thermogenesis interacting with the sympathetic nervous system (SNS) at various levels. Peripherally, thyroid hormone potentiates the effects of the SNS at the level of the adrenergic receptor and adenylyl cyclase complex as well as distal from this point. Synergistic interactions between T3 and cAMP on the regulation of gene expression have been described. Brown adipose tissue (BAT) T4-5'-deiodinase plays a central role in controlling heat production. When this enzyme is stimulated by norepinephrine in the euthyroid and hypothyroid condition, it provides high concentrations of T3 to BAT; inhibition by T4 in hyperthyroidism may limit brown fat thermogenic responses. Also, thyrotoxicosis uniquely reduces the expression of beta 3-adrenergic receptors in brown adipose tissue, and the increased obligatory thermogenesis of this condition, via afferent neural pathways, may reduce the hypothalamic stimulation of brown fat, providing additional mechanisms to limit brown adipose tissue thermogenesis in hyperthyroidism.

Effects of thyroid hormone on norepinephrine signaling in brown adipose tissue. I. Beta 1- and beta 2-adrenergic receptors and cyclic adenosine 3',5'-monophosphate generation

Brown adipose tissue (BAT) thermogenesis is activated by the sympathetic nervous system. BAT responses to norepinephrine are blunted in hypothyroidism and are rapidly restored by thyroid hormone. We examined in rats the effects of thyroid hormone on BAT beta 1- and beta 2-adrenergic receptors (AR) expression and capacity to generate cAMP in response to adrenergic stimulation. Both are reduced in hypothyroidism. The reduction in cAMP generation is equal to or greater than that in beta 1,2-AR; it is the same whether cAMP production is stimulated with norepinephrine, selective beta 3-AR agonists, or forskolin; and it is not affected by the inhibition of phosphodiesterase. Both beta 1,2-AR and the capacity to generate cAMP were slowly corrected by thyroid hormone. T3 normalized beta 1,2-AR between 1 and 2 days, whereas the improvement in cAMP generation lagged 1 or 2 days behind. Within 2 days of acclimation of athyreotic rats at 30 C, the number of beta 1,2-AR reached the euthyroid level, whereas exposure to 4 C decreased these receptors. We reached the following conclusions: 1) BAT beta 1,2-AR and capacity to generate cAMP are reduced in hypothyroidism; 2) the latter, however, is not explained by the reduction in beta 1,2-AR, but, rather, reflects a fault at the postreceptor level; 3) the reduction in beta 1.2-AR number is largely caused by the cold stress derived from the low metabolic rate of the hypothyroid state; and 4) the slow restoration of both receptor number and capacity to generate cAMP after T3 are not consistent with these defects being a significant factor in the previously reported blunted uncoupling protein responses to adrenergic stimulation in hypothyroidism.

Thyroid hormone and norepinephrine signaling in brown adipose tissue. II: Differential effects of thyroid hormone on beta 3-adrenergic receptors in brown and white adipose tissue

beta 3-adrenergic receptors (AR) are predominantly expressed in brown (BAT) and white adipose tissue (WAT), being more abundant in the former. There is growing interest in these receptors because of their potential to be pharmacologically targeted to control energy expenditure and lipid accretion. We have examined, in BAT and WAT of rats, the effect of thyroid hormone on the expression of beta 3-AR and their contribution to cAMP generation. Receptor density was assessed with the nonselective beta 3-AR ligand [125I]-cyanopindolol ([125I]-CYP) and the highly selective beta 3-AR agonist CL3216,243. beta 3-AR messenger RNA (mRNA) was analyzed by Northern blotting of total BAT and WAT RNA. Generation of cAMP by brown adipocytes in response to norepinephrine (NE) and CL316,243 was measured by RIA. In BAT, beta 3-AR can account for as much as 50% of the maximal cAMP response to NE, whereas in WAT these receptors probably account for all the effect of NE. In hypothyroidism. BAT beta 3-AR number is increased, as are beta 3-AR mRNA (4- to 6-fold) and the relative contribution of these receptors to the maximal cAMP production. In contrast, both beta 3-AR number and mRNA levels are reduced in WAT of hypothyroid rats. The injection of T3 to hypothyroid rats reverts the changes in beta 3-AR within 24 h, and T3 excess causes a greater than 90% reduction in beta 3-AR mRNA in BAT but a 5-fold increase in WAT. In both tissues, hypothyroidism is associated with a marked reduction in the capacity to generate cAMP, but this is not completely restored even after 2 days of a receptor-saturating dose of T3.

CONCLUSIONS

1) thyroid hormone differentially affects the expression of beta 3-AR in BAT and WAT; 2) these effects of T3 are both rapid and marked and seem to take place at a pretranslational level; 3) in both tissues there is a postreceptor defect in the generation of cAMP that is corrected by T3 much later after the changes in beta 3-AR are reversed; and 4) thyroid hormone is among the known factors that most vigorously affect the expression of beta 3-AR.

Delineation of thyroid hormone-responsive sequences within a critical enhancer in the rat uncoupling protein gene

Uncoupling protein (UCP) is essential to brown adipose tissue (BAT) thermogenesis and, hence, to cold adaptation and energy balance. The sympathetic nervous system, via norepinephrine and cAMP, and thyroid hormone seem to be the major regulators of UCP expression. T3 potentiates the effect of norepinephrine and is essential for the adaptive response of this protein to cold. The goal of the present studies was to investigate whether T3 directly stimulates the transcription of the rat UCP gene, as suggested by in vivo results, and if so, to identify and characterize the sequences involved. We examined the gene sequence between 114 and -3623 by transient transfection analysis in JEG-3 and HIB-1B cells, a BAT-derived cell line. This 3.7-kilobase UCP insert makes the reporter gene responsive to cAMP (4-fold), T3 (4-fold), or both combined (12-fold). We identified an 82-basepair (bp) restriction fragment between -2317 and -2399, which we called thyroid hormone response sequence (THRS), that conferred T3 responsiveness to the UCP minimal promoter (4- to 12-fold) as well as to the thymidine kinase promoter (3- to 6-fold). T3 receptor bound to THRS in vitro, retarding its migration in electrophoretic mobility shift assays. Footprinting of THRS revealed two potential thyroid hormone response elements (TRE) separated by 27 bp: upTRE, -2391/-2376, 5'ACCCCTACTGAGGCAA; and dnTRE, -2348/-2334, 5'AGGGCAGCAAGGTCA. The mutation of these putative TREs caused loss of both T3 receptor binding and transactivation by T3. The analysis of the mutants also demonstrated that both TREs contribute in similar proportion to the T3 responsiveness of the UCP gene and that dnTRE is necessary for the potentiation of the cAMP effect by T3. Both TREs are located within a previously identified 212-bp enhancer element, flanked by sequences considered essential for BAT expression and norepinephrine responsiveness. Although they do not mediate thyroid hormone responsiveness, the sequences flanking THRS increase basal reporter expression and enhance the responses to T3. In conclusion, our results indicate that T3 can stimulate the transcription of the UCP gene and amplify the effect of cAMP acting directly on the gene. The presence of two functional TREs in a location critical to the control of the gene supports the importance of thyroid hormone for its expression and suggests the potential for interactions at the gene level that may explain the complexity of UCP regulation in vivo.

Thyroid hormone receptors and 3,5,3'-triiodothyronine biological effects in FRTL5 thyroid follicular cells

Specific thyroid hormone (T3) receptors are present in thyroid follicular cells, including the rat FRTL5 clonal line, but little is known about the effects of T3 on the growth and differentiated function of the thyroid. Unlike primary cultures of animal or human thyroid cells, FRTL5 do not secrete appreciable amounts of thyroid hormones. We now have studied the effects of T3 by itself and in combination with TSH and insulin-like growth factor-I (IGF-I) on [3H]thymidine incorporation into DNA, iodide uptake, and cAMP production in FRTL5. We also have investigated the expression of different c-erbA mRNAs in these cells. Specific binding of T3 to FRTL5 cell nuclei in intact cells occurred with a binding capacity of 0.1-0.15 ng T3/mg DNA and an apparent Kd of 0.4 nM. Using an RNase protection assay on total cellular FRTL5 RNA and specific cRNA probes, we demonstrated the presence of c-erbA alpha and -beta mRNAs, both encoding T3 receptors. Biological effects were assessed in serum-free medium or buffer containing 0.1% BSA after maintaining quiescent culture of cells for at least 5 days in hormone-free medium containing 5% calf serum. T3 alone stimulated a dose-dependent increase in [3H]thymidine incorporation that reached a plateau at 188% of the control value at 10 nM T3. At 10(-11) M TSH, T3 potentiated TSH-stimulated [3H]thymidine incorporation (2.2-fold), but at TSH concentrations greater than 5 x 10(-11) M, T3 had no effect or reduced the response to TSH. T3 potentiated the [3H]thymidine response to 2 and 10 ng/ml IGF-I by 1.5- to 1.7-fold. T3 alone had no effect on iodide uptake, but attenuated iodide uptake stimulated by TSH. T3 was more potent in inhibiting TSH-stimulated iodide uptake than in enhancing TSH-stimulated DNA synthesis. T3 did not affect either basal or TSH-stimulated cAMP accumulation. Thus, in FRTL5 thyroid follicular cells 1) T3 receptors are expressed, as measured by direct binding assays and by the expression of c-erbA mRNAs; and 2) T3 acts as a growth factor and weak antidifferentiation factor. We suggest that T3 may modulate the actions of TSH and growth factors in thyroid epithelium.

Adenosine 3',5'-monophosphate and thyroid hormone control of uncoupling protein messenger ribonucleic acid in freshly dispersed brown adipocytes

We intend to develop in vitro model systems to study the hormonal regulation of uncoupling protein (UCP) and its role in brown adipose tissue (BAT) thermogenesis. We report here that UCP mRNA responses to adrenergic and thyroid hormone manipulations in freshly dispersed, mature brown adipocytes mimic in vivo observations. Studies were performed in brown adipocytes obtained from interscapular brown fat of euthyroid or hypothyroid rats. The tissue was dispersed with collagenase, and cells were isolated by floatation over 4% BSA. UCP mRNA in these cells is 2-3 times more abundant than that in the whole tissue, indicating a selection of cells expressing the gene. In cells from euthyroid rats, UCP mRNA is maximally elevated within 2 h of exposure to 1 microM forskolin and 50 ng T3/ml (77 nM total, 0.43 nM free). T3 significantly enhances the effect of forskolin. In the absence of stimulation, UCP mRNA rapidly disappears from euthyroid brown adipocytes, and this can be prevented with the addition of T3 by a mechanism not requiring on-going transcription. In cells from hypothyroid rats, forskolin or isoproterenol plus phenylephrine fail to stimulate UCP mRNA, but within 3 h of exposure to T3, cells recover full responsiveness. As in vivo, a high extracellular concentration of T3 is required for maximal responsiveness of UCP mRNA to cAMP, while T4 can restore responsiveness in physiological concentrations (40 pM). This effect of T4 is prevented by iopanoic acid, a compound that blocks the type II T4 5'-deiodinase. In conclusion, 1) freshly dispersed brown adipocytes retain all of the properties concerning UCP regulation by thyroid hormone and sympathetic nervous system described for brown fat in vivo; 2) the observations made in vivo, thus, represent direct action of norepinephrine and thyroid hormone on these cells; 3) as in vivo, T4 is a better source of intracellular T3 than extracellular T3 for brown adipocytes; hence, the in vivo findings are the result of the cell biology of 5'-deiodinase type II rather than dynamic factors inherent to the in vivo condition; 4) stabilization of mature UCP mRNA by T3 is an important mechanism to maintain the levels of this mRNA elevated under sustained stimulation; and 5) dispersed brown adipocytes and UCP gene products constitute a powerful model to study interactions between the sympathetic nervous system and thyroid hormone at a cellular or molecular level.

Transcriptional and posttranscriptional mechanisms in uncoupling protein mRNA response to cold

Three mechanisms account for the rapid elevation and maintenance of uncoupling protein (UCP) mRNA levels in cold-exposed rats, namely, an increase in the rate of transcription initiation, an increase in the fraction of nascent UCP transcripts undergoing elongation, and stabilization of the mature UCP mRNA. The second mechanism precedes and outlasts the increase in the rate of UCP gene transcription, which is brisk but short lived. After 48 h of cold exposure, mature UCP mRNA levels are maintained elevated solely on the basis of stabilization, since the levels of both transcription initiation and fifth intron-containing transcripts (precursors) have returned to basal. Results in hypothyroid rats given 3,5,3'-triiodothyronine (T3) and in dispersed brown adipocytes show that T3 is involved both in the increase in UCP mRNA precursor level and stabilization of mature UCP mRNA. These mechanisms are rapidly reversed when the rats are returned to thermoneutrality. These coordinated transcriptional and post-transcriptional mechanisms modulating UCP gene expression ensure a rapid increase in the concentration of UCP and prevent further accumulation of the protein as physiologically adequate levels are attained.

Central role of brown adipose tissue thyroxine 5'-deiodinase on thyroid hormone-dependent thermogenic response to cold

As judged by the response of uncoupling protein and key enzymes, brown adipose tissue (BAT) is highly dependent upon the local generation of T3 catalyzed by the tissue type II T4 5'-deiodinase (5'-D-II). In hypothyroid rats treated with T3 or T4, the capacity to withstand cold seems better correlated with the normalization of BAT responses than with the liver thyroid status. 5'D-II is activated by cold via sympathetic nervous system (SNS) stimulation, and the activation generates enough T3 to nearly saturate BAT nuclear T3 receptor (NTR) in euthyroid rats. In hypothyroidism, 5'D-II is highly stimulated by the SNS and hypothyroxinemia. In the present studies we have taken advantage of this situation to test 1) the capacity of 5'D-II to maintain nuclear T3 in rats with various degrees of hypothyroxinemia, and 2) the hypothesis that thyroid hormone-dependent BAT-facultative thermogenesis, rather than the effect of thyroid hormone on obligatory thermogenesis (basal metabolic rate), is the basic mechanism by which thyroid hormone confers protection against acute cold exposure. We treated methimazole-blocked rats (undetectable plasma T4 and T3) for a week with either subreplacement doses of T4 (0.5, 1, 2, and 4 micrograms/kg.day) or replacement doses of T4 or T3 (8 or 3 micrograms/kg.day, respectively). Sources and content of BAT nuclear T3 were studied at 25 C and after 48 h at 4 C by labeling the plasmaborne T3 (T3[T3]) with [131I]T3 and the locally generated T3 (T3[T4]) with [125I]T4. Neither the kinetics of nuclear-plasma exchange of T3[T3], the time of appearance of T3[T4] in BAT nuclei, nor NTR maximal binding capacity (0.71 ng T3/mg DNA) was affected by hypothyroidism. Kinetic analyses indicated a maximal BAT NTR occupancy of 40% at euthyroid serum T3 concentrations if T4 is not present. Replacement with T4 normalized both serum T4 and T3, while replacement with T3 normalized serum T3; for all other doses of T4, serum T4 and T3 concentrations were predictably related to the dose. 5'D-II activity decreased with increasing doses of T4, but for each dose of T4, this activity was 2-4 times greater at 4 C than at 25 C. BAT NTR occupancy normalized with 2 micrograms T4/kg in rats maintained at 25 C and with 4 micrograms T4/kg in cold-exposed rats, although in neither condition were serum T4 and T3 normalized nor more than 30% of NTR occupied by plasma T3.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of iodine deficiency and cold exposure on thyroxine 5'-deiodinase activity in various rat tissues

We measured thyroxine 5'-deiodinase I (T(4)5'D-I) activity in thyroid, liver, and kidney and thyroxine 5'-deiodinase II (T(4)5'D-II) activity in brown adipose tissue (BAT) in rats on a low-iodine diet (LID) to test the possibility that increased deiodinase activity in these tissues might contribute to the maintenance of ther serum 3,5,3'-triiodothyronine (T3) level. Control rats received LID plus KI. Experiments were also performed with LID and LID plus KI rats exposed to cold. T(4)5'D-I activity was greatly increased in the thyroids of LID rats but not in liver or kidney. We consider it likely that increased thyroxine (T4)-to-T3 conversion in the greatly enlarged thyroids of LID rats contributed to the maintenance of serum T3. T(4)5'D-II activity in BAT was markedly increased in LID rats and was further greatly increased on cold exposure. However, we were unable to demonstrate an increase in uncoupling protein mRNA levels in BAT in response to cold in LID rats. We attribute this to the very low serum T4 level, which limits substrate availability. This factor also makes it unlikely that BAT contributes to maintenance of serum T3 in LID rats.

Immunoglobulins of patients recovering from Yersinia enterocolitica infections exhibit Graves' disease-like activity in human thyroid membranes

Substantial evidence suggests a link between infections with Yersinia enterocolitica (YE) and Graves' disease. We have now examined the sera of 72 patients recovering from YE infection for immunoglobulins that interacted with the TSH receptor in human thyroid membranes. Compared with controls, in concentrations between 1 and 4 mg/mL, patient IgG produced a significant, concentration-dependent inhibition of TSH binding (p less than 0.001) and stimulation of adenylate cyclase activity (p less than 0.005-0.05). Whereas IgG from normal individuals caused no stimulation of adenylate cyclase, IgG from controls caused some concentration-dependent displacement of TSH, as previously reported. However, IgG from convalescents of YE infections was significantly more potent than normal IgG in reducing the binding of TSH to the membrane. Thus, at each examined concentration, YE patients' IgG displaced more TSH than IgG from normal controls. For each milligram per milliliter increment of IgG in the assay, patients' IgG caused a 10.2% inhibition of TSH binding (r -0.90, p less than 0.001), significantly greater than that seen with normal IgG (p less than 0.02). The present studies provide the first demonstration that IgG of patients recovering from YE infections react with the human TSH receptor. The antibodies presumably are produced against the TSH-binding protein present in YE. However, in view of lack of evidence for thyroid dysfunction in the sera of patients recovering from yersiniosis and the presence of TSH-binding proteins in other bacteria, we postulate that infection with YE is neither necessary nor sufficient to cause thyroid autoimmune disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors determining the differential tissue response of Na/K-ATPase to thyroid hormone in the neonatal rat

The concentration of ouabain binding sites (OBS), a measure of the abundance of sodium/potassium-dependent ATPase (Na/K-ATPase), was measured in cerebral cortex (CC), cerebellum (CBL), brown adipose tissue (BAT), and heart of neonatal rats with congenital hypothyroidism. In euthyroid rats, the concentration of OBS was 50- to 100-fold greater in the nervous tissue than in the nonnervous tissue. Congenital hypothyroidism resulted in a significant reduction in the number of OBS in all four tissues. Although in absolute terms (pmol/mg protein) the reduction was greater in the nervous tissues, in relative terms it was much greater in the nonnervous tissues. The restoration of OBS concentration was much more sensitive to T4 in CC, CBL, and BAT than in heart. In contrast, the response of OBS concentration to T3 in hypothyroid rats was greater in the heart, followed by the BAT and CBL, being minimal in CC. The sensitivity to T4 replacement correlated with the degree of the stimulation of the type II 5'deiodinase (5'D-II) by hypothyroidism, whereas the response to exogenous T3 correlated with the fraction of the tissue T3 that derives from plasma T3 and inversely with the plasma T3 concentration required to saturate 50% of the nuclear receptors as reported in previous studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of total sleep deprivation on 5'-deiodinase activity of rat brown adipose tissue

Prolonged sleep deprivation of the rat produces a progressive increase in energy expenditure and an eventual decrease in body temperature, which suggests a profound derangement in thermoregulation. Because increased thermogenic activity in brown adipose tissue (BAT) is a likely mechanism mediating the observed increase in energy expenditure, we focused our attention on the effect of total sleep deprivation on BAT type II 5'-deiodinase (5'D-II), since its activation indicates BAT stimulation and is essential for full BAT thermogenic response. Five euthyroid rats were subjected to total (92%) sleep deprivation (euD-rats). Sharing the sleep deprivation apparatus, yoked control rats (euC-rats) received the same degree of physical stimulation as the D-rats, but were only partially (25%) sleep deprived. Additional cage controls (euCC-rats) were housed in the same room. Since during sleep deprivation the animals undergo a reduction in plasma T4 concentration and inability to maintain body temperature heralds death, an identical study was performed in five trios of hyperthyroid rats (hyperD-, hyperC-, and hyper CC-rats) given daily ip injections of 15 micrograms T4/100 g BW, 10 days before and throughout the deprivation period. Experiments were carried out at an ambient temperature of 29 C, close to thermoneutrality for rats. Sleep deprivation in hyperD-rats was maintained until death seemed imminent (9-14 days), and in euD-rats for 12-15 days. Sleep deprivation induced a significant increase in BAT 5'D-II activity in both hyperD- and euD-rats compared with that in euCC-rats (P less than 0.01). BAT 5'D-II in euC-rats was also significantly higher than that in euCC-rats (P less than 0.05), probably because they were partially sleep deprived. BAT 5'D-II activity in hyperD-rats was increased compared to that in both hyperC- and hyperCC-rats (P less than 0.05), in which the activity was slightly but not significantly lower than that in euCC-rats. No significant differences were observed in liver and kidney type I 5'-D (5'D-I) and in pituitary 5'D-II among euD-rats, euC-rats, and euCC-rats. As expected, the hyperthyroid groups (hyperD-rats, hyperC-rats, and hyperCC-rats) had significantly higher kidney 5'D-I and lower pituitary 5'D-II than the euCC-rats. Liver 5'D-I was also significantly increased in the hyperC-rats and hyperCC-rats, but not in the hyperD-rats. These observations indicate that total sleep deprivation is associated with a marked increase in BAT 5'D-II activity in both euthyroid and hyperthyroid rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Iodothyronine deiodinase activities in FRTL5 cells: predominance of type I 5'-deiodinase

FRTL5 cells, a thyroid follicular cell line derived from normal rat thyroid, has been extensively used as a model system to study various aspects of the physiology of the thyroid epithelium. The capacity of these cells to metabolize iodothyronines and to generate T3 from T4 has not been previously examined. Here we studied the deiodination of T4, T3, and rT3 in homogenates of FRTL5 cells. By far, these homogenates were more potent catalyzing the 5'-deiodination (outer ring) of T4 and rT3 than the inner ring deiodination of T4 or T3. Both the production of rT3 and the degradation of newly formed T3 from T4 were very limited. Thus, when T4 was used as a substrate, T3 and iodide accumulated in a linear fashion with time, and initially the amounts of iodide and T3 were approximately equal. rT3 and 3,3'-diiodothyronine were rapidly deiodinated by these homogenates, with the 3'-deiodination of 3,3'-diiodothyronine occurring at a slower rate than the 5'-deiodination of rT3. The iodothyronine 5'-deiodinase activity corresponded to type I, as indicated by the following: the Km for T4 and T3 was in the micromolar range; rT3 was a better substrate than T4 (maximum velocity = 101 vs. 19 pmol/min.mg protein; Km = 0.83 vs. 3.1 microM, respectively); and the kinetics of inhibition by 6n-propyl-2-thiouracil were uncompetitive and substrate dependent, suggesting ping-pong kinetics. The type I 5'-deiodinase activity of FRTL5 cells was distinctly stimulated by TSH. This stimulation seems to be mediated by cAMP and requires serum as a permissive factor. In conclusion, 1) FRTL5 cells exhibit both inner and outer ring iodothyronine-deiodinating activities; 2) iodothyronine 5'-deiodination is by far more active; 3) the 5'-deiodination has been characterized as type I deiodinase based on substrate preference, enzyme kinetics, and inhibitors; 4) in all respect iodothyronine deiodination by FRTL5 cell homogenates proceeded with marked similarity to that in homogenates or microsomes of thyroid glands from several species; and 5) the FRTL5 type I deiodinase is more active than that reported in thyroid tissue and as active as that reported in liver and kidney, the prototype of type I deiodinase-containing tissues. The present studies indicate that FRTL5 cells are an excellent model system to study cellular and biochemical aspects of the regulation of this enzyme as well as its regulation by TSH and putative serum factors.

Effects of congenital hypothyroidism on microtubule-associated protein-2 expression in the cerebellum of the rat

In view of the defective neurotubule assembly observed in congenital hypothyroidism and the striking morphological abnormalities of the cerebellum in this condition, we have investigated the expression of microtubule-associated protein-2 (MAP2) in the cerebellum of rats with congenital hypothyroidism. Analysis included the measurement of immunoreactive MAP2 and its mRNA. In addition, the intracellular distribution of MAP2 was studied by immunostaining of the appropriate histological preparations. The results showed that the developmental increase in MAP2 is delayed in congenital hypothyroidism, but eventually the concentration of this protein reached normal levels in animals with this condition, even if untreated. These abnormalities in the immunoreactive protein are not paralleled by abnormalities in the abundance of MAP2 mRNA, which was not affected by the thyroid status of the animals. In spite of the normalization of the content of the protein, the distribution of MAP2 in the Purkinje cells of hypothyroid rats remained abnormal. Whereas in euthyroid rats the protein rapidly migrated into the dendrites, in the Purkinje cells of hypothyroid pups, MAP2 remained largely confined to the body and the most proximal part of the dendrites. These results suggest that thyroid hormone affects the expression of MAP2 at translation or posttranslational levels. The abnormality in distribution may result from some posttranslational abnormality of the protein itself or some underlying defect in the function of the neurons. These observations are probably relevant to the abnormalities in cerebellar function seen in animals and humans with untreated congenital hypothyroidism.

Thyroid nodularity after childhood irradiation for lymphoid hyperplasia: a comparison of questionnaire and clinical findings

Ionizing radiation is a well-established cause of thyroid cancer and nodularity, however, important questions relating to the magnitude of the risk following low-dose medical exposures remain unresolved. To address these issues, we conducted a follow-up study of 1590 individuals treated between 1938 and 1969 with X-rays for childhood lymphoid hyperplasia (av. thyroid dose = 24 cGy) and 1499 individuals treated with surgery only. Thyroid nodularity was determined from self-administered questionnaires completed by 1195 irradiated and 1063 surgically-treated subjects and from clinical examinations of 602 irradiated and 457 non-irradiated subjects. A much higher relative risk (RR) for radiation-induced thyroid nodules was estimated from the questionnaire than from the clinical examination data, 15.8 and 2.7, respectively. (The corresponding estimates of excess RR per cGy were 64 and 7%). Analysis of the examination data revealed a strong dose-response relationship, similar excess RR/cGy for males and females, and an inverse relationship with age at exposure. Although the thyroid gland is one of the most sensitive organs to the neoplastic effects of radiation, the radiation-induced risk of thyroid nodularity reported from questionnaire studies may over-estimate the true risk.

Acute thyroxine ingestion in pediatric patients

During a 1-year period, 15 cases of acute thyroxine (T4) overdose with documented serum T4 concentrations were studied. All patients were less than 5 years of age and 80% were boys. All were examined within 1 to 6 hours of ingestion and all were asymptomatic. Estimated dose ingested in 10 patients ranged from 1.5 to 8.8 mg (0.1 to 0.73 mg/kg). Three patients with initial T4 serum concentrations greater than 75 micrograms/dL manifested signs of toxicity within 12 to 48 hours (fever, tachycardia, hypertension, and/or agitation) that resolved within 24 to 60 hours. The mean elimination half-life of T4 in 7 patients with multiple serum concentrations was 2.8 +/- 0.4 days, whereas the mean elimination half-life of triiodothyronine was 6 +/- 1.7 days. It was concluded that (1) the majority of acute pediatric T4 overdoses are not severe and may be managed on an outpatient basis, (2) the absence of early clinical manifestations does not preclude delayed onset of toxicity that may be better predicted by initial T4 concentrations, and (3) the elimination half-life of T4 is shorter and the elimination half-life of tri-iodothyronine is longer than with therapeutic doses.

Effect of thyroid status on catecholamine stimulation of thyroxine 5'-deiodinase in brown adipocytes

We examined type II 5'-iodothyronine deiodinase activation by adrenergic agonists in dispersed brown adipocytes from euthyroid and hypothyroid rats. In euthyroid cells, basal deiodinase activity was 30-100 fmol I-.h-1.10(6) cells-1 and increased four- to fivefold during exposure to norepinephrine, an effect that was enhanced by alprenolol. In cells from hypothyroid rats, norepinephrine caused a three- to fourfold greater deiodinase stimulation than occurred in euthyroid cells but alprenolol inhibited the response. In euthyroid cells, phenylephrine caused greater stimulation than did norepinephrine, but this was inhibited by alprenolol. Isoproterenol and 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) inhibited the phenylephrine response but were modestly stimulatory alone. Although both alpha 1- and beta-adrenergic agonists increased deiodinase activity modestly in hypothyroid cells, in combination they caused a marked synergistic stimulation. This synergism was induced by 8-BrcAMP and forskolin, as well as by isoproterenol. The stimulation of deiodinase in both cell types was due to an increase in Vmax without an alteration in the Km and required mRNA synthesis. The markedly greater deiodinase response of the hypothyroid brown adipocyte to catecholamines may serve to enhance the impaired thermogenic response of this tissue to cold exposure.