Biomedical subjects

F Goglia

Publications and source records attributed to F Goglia.

At least 37 records · Page 2Linked to original sources

PubMed1998

3,5-Diiodo-L-thyronine and 3,5,3'-triiodo-L-thyronine both improve the cold tolerance of hypothyroid rats, but possibly via different mechanisms.

The effects of 3,5-diiodo-L-thyronine (3,5-T2, 2.5-10 microg/100 g BW) on cold tolerance, energy expenditure and oxidative capacity of four metabolically very active tissues (brown adipose tissue, skeletal muscle, liver and heart) were determined in hypothyroid, cold-exposed rats. Hypothyroid rats survived cold for only 3-4 days. 3,5-T2 improved survival dose dependently; with 10 microg/100 g BW the rats survived 3 weeks (limit of observation). This effect was paralleled by an increased energy expenditure of the whole animal for the entire 3 weeks. Similar effects were observed in hypothyroid rats treated with 3,3',5-triiodo-L-thyronine (T3). 3,5-T2 stimulated the specific oxidative capacity (expressed as cytochrome oxidase activity per milligram protein) of all four tissues dose dependently. When the oxidative capacity was expressed as total activity (cytochrome oxidase activity times organ weight), the percentage increases were of the same order. T3 exerted similar effects, but the changes in total activity were much greater than in specific activity, indicating an effect on the tissue trophism. The effect of 3,5-T2 on cold tolerance thus mimics the effect of T3, but via different cellular mechanisms. T3 seems to act primarily on the trophism of the tissues, while 3,5-T2 may act directly on mitochondria without an effect on tissue trophism.

Adaptation, Physiological↗

PubMed1998

Effect of 3,5-diiodo-L-thyronine on thyroid stimulating hormone and growth hormone serum levels in hypothyroid rats.

We have investigated the biological effects of physiological doses of 3,5-diiodo-L-thyronine (3,5-T2) and 3,3'-diiodo-L-thyronine (3,3'-T2) (at doses from 2.5 to 10 microg/100 g BW) on serum TSH and GH levels in rats made hypothyroid by propylthiouracil and iopanoic acid administration. In such animals deiodinase activities were inhibited and thyroid hormones serum levels strongly reduced. The effects of T2s were compared with those elicited by 3,5,3'-triiodo-L-thyronine (T3) (2.5 microg/100 g BW).The serum TSH level was much greater in hypothyroid rats than in euthyroid ones. T3 administration suppressed TSH by 88% compared to control (i.e, the level in hypothyroid rats); it thus reached a value not significantly different from that seen in the euthyroid rats. 3,5-T2 produced a similar effect, suppressing the TSH level by about 75% compared to control; it thus reached values not significantly different from those of the euthyroid and T3-treated rats. By contrast, 3,3'-T2 had no effect on TSH, whatever the dose. The serum GH level was much lower in hypothyroid rats than in euthyroid ones. T3 administration increased the GH level by about 5-fold, restoring it to the value seen in euthyroid rats. 3,5-T2-treated hypothyroid rats, at all the doses used (from 2.5 to 10 microg/100 g BW), showed increased serum GH levels: at a dose of 10 microg/100 g BW the level reached a value about 5-fold higher than that in hypothyroid rats. This value was not significantly different from those of euthyroid and T3-treated rats. 3,3'-T2 did not affect GH levels whatever the dose. Thus, 3,5-T2 (but not 3,3'-T2) seems to mimic the effects of T3 on serum TSH and GH levels in rats.

Animals↗

PubMed1998

Monosynaptic pathway between the arcuate nucleus expressing glial type II iodothyronine 5'-deiodinase mRNA and the median eminence-projective TRH cells of the rat paraventricular nucleus.

Recent evidence suggests that the thyroid regulation of thyrotropin-releasing hormone (TRH)-containing neurons in the paraventricular nucleus of the hypothalamus involves the activation of other hypothalamic neural circuits. For example, the arcuate nucleus and not the paraventricular nucleus contains the highest enzyme activity of 5'-deiodinase type II, an enzyme that is pivotal for the local synthesis of T3. This experiment was undertaken to demonstrate whether a monosynaptic pathway exists between the arcuate nucleus and those TRH cells of the paraventricular nucleus that are neuroendocrine, i.e. project to the external layer of the median eminence. A specific cRNA probe derived from the coding region of deiodinase type II was used for the in situ hybridization histochemistry which was combined with immunocytochemistry for a specific marker of glial cells, glial fibrillary acidic protein (GFAP). The hybridization signals were present within the hypothalamus in the arcuate nucleus-median eminence region and in the periventricular area. The periventricular labeling was localized to the ependymal layer of the third ventricle and no hybridization product was detected in the paraventricular nucleus and other hypothalamic nuclei adjacent to the third ventricle. Within the median eminence, numerous cells containing the hybridization product were located in the internal layer adjacent to the floor of the third ventricle and in the external layer adjacent to the surface of the brain. In the dorso- and ventromedial regions of the arcuate nucleus, deiodinase type II mRNA-containing cells were also detected. Numerous type II deiodinase mRNA-containing cells in the median eminence and arcuate nucleus were also found to be immunopositive for GFAP. The abundance of arcuate cells expressing the hybridization product was lower than those in the periventricular region or in the median eminence. The anterograde tracer, Phaseolus vulgaris leucoagglutinin, was injected into the medial parts of the arcuate nucleus where the in situ hybridization experiment detected deiodinase type II mRNA. Simultaneously with the anterograde tracing, the retrograde tracer, Fluoro-Gold, was injected into either the median eminence or the general circulation. Light and electron microscopic double and triple immunolabeling experiments on vibratome sections of colchicine-pretreated animals revealed that arcuate fibers innervate TRH cells within the parvicellular region of the paraventricular nucleus. Populations of these TRH cells receiving afferents from the arcuate nucleus were also retrogradely labelled from either the median eminence or the general circulation indicating their direct role in the regulation of thyrotropin secretion from the anterior pituitary. The majority of arcuate nucleus efferents on TRH cells were found to establish symmetrical synaptic connections. The present results provided direct evidence of a monosynaptic pathway between the hypothalamic site of local thyroid hormone production, the arcuate nucleus, and neuroendocrine TRH cells in the paraventricular nucleus. This signalling modality may play an important role in thyroid feedback on TRH cells. Since the arcuate nucleus is involved in the regulation of central mechanisms controlling diverse homeostatic functions, including reproduction and feeding, the pathway described in this study may also carry integrated signals related to reproduction and ingestion to TRH-producing cells.

Animals↗

PubMed1998

Fasting-induced increase in type II iodothyronine deiodinase activity and messenger ribonucleic acid levels is not reversed by thyroxine in the rat hypothalamus.

The importance of local formation of T3 in the feedback effect of the thyroid gland on hypothalamic TRH-producing cells has been established. Primary failure of the thyroid gland results in a fall in circulating T4 and T3 levels, leading to an elevation in the production and release of TRH in the hypothalamic paraventricular nucleus. In contrast, during short term fasting, declining plasma levels of thyroid hormones coincide with suppressed TRH production and release. In the brain, the prevalent enzyme that converts T4 to T3 is type II iodothyronine deiodinase (DII). The present study was undertaken to determine whether a differential hypothalamic expression of type II deiodinase may exist in fasted rats and in animals that are hypothyroid due to the failure of the thyroid gland. Using in situ hybridization, we assessed type II deiodinase messenger RNA (mRNA) levels in the hypothalamus of rats that were control euthyroid, hyperthyroid (T4), hypothyroid induced by propylthiouracil (PTU), and fasted. A group of fasted rats also received exogenous T4. DII mRNA was detected around the third ventricle, including the ependymal layer and adjacent periventricular regions as well as in the arcuate nucleus and the external layer of the median eminence. Quantitative in situ hybridization analysis demonstrated that PTU treatment and short term fasting resulted in significant elevations in DII messenger levels compared with those in euthyroid controls. Three weeks of PTU administration induced a consistent decline in circulating T3 and undetectable T4 levels, whereas 3 days of fasting resulted in only a 50% fall in the concentration of serum thyroid hormones. Interestingly, however, the expression of the DII mRNA was more than 2-fold higher in fasted animals compared with the values in PTU-treated rats. Furthermore, although T4 administration repressed DII mRNA expression in euthyroid animals, the same treatment had no effect on the fasting-induced elevations of DII message. To assess whether DII enzymatic activity is also affected during food deprivation, hypothalami were dissected out, and DII activity was measured in control euthyroid, fasted, and fasted plus T4-treated rats. To determine whether comparable changes in plasma thyroid hormone levels induced by fasting and PTU treatment could have affected DII enzymatic activity in a similar manner, animals were injected ip with PTU for 5 days to decrease plasma thyroid hormones to levels similar to those caused by fasting. DII enzymatic assay showed a significant increase in DII activity in fasted and fasted plus T4-treated animals compared with those in euthyroid controls and PTU-treated rats. No significant changes were found in PTU-treated rats compared with euthyroid animals. These data indicate that during short term fasting, a signal of nonthyroid origin underlies the robust elevation of DII production and activity in the hypothalamus. Thus, we propose that during the initial phase of food deprivation, an increased negative thyroid feedback exists on the hypothalamus due to locally formed T3. This local hyperthyroidism may, in turn, induce the suppression of TRH under these conditions.

Animals↗

PubMed1997

How the thyroid controls metabolism in the rat: different roles for triiodothyronine and diiodothyronines.

1. Although the first evidence of a relationship between the thyroid and metabolism was reported in 1895, the mechanism by which thyroid hormones influence resting metabolic rate in whole animals is still poorly understood. This paper reports an attempt to test whether diiodothyronines (T2s) and triiodothyronine (T3) have different roles in the control of resting metabolism (RM). 2. Changes in resting metabolic rate were measured in hypothyroid rats treated acutely (25 micrograms (100 g body weight)-1) either with one of the T2s or with T3. Injection of T3 induced an increase of about 35% in RM that started 25-30 h after the injection and lasted until 5-6 days after the injection, the maximal value being observed at 50-75 h. The injection of T2s evoked a temporally different pattern of response. The increases in RM started 6-12 h after the injection, had almost disappeared after 48 h, and the maximal stimulation was observed at 28-30 h. 3. When actinomycin D (an inhibitor of protein synthesis) and T3 were given together, the stimulation of RM was almost completely abolished. The simultaneous injection of actinomycin D and either of the T2s, on the other hand, did not cause any attenuation of the stimulation seen with the T2s alone. 4. Following chronic treatment (3 weeks) with either T3 or T2s there was a stimulation of organ growth only after the administration of T3. 5. Chronic administration of either T2s or T3 to hypothyroid rats significantly enhanced the oxidative capacity of each of the tissues considered. In the case of T2s the stimulation was almost the same whether it was expressed as an increase in specific activity or total tissue activity. In the case of T3 the increases were, in the main, secondary to the hypertrophic or hyperplastic effect. 6. These results indicate that T2s and T3 exert different effects on RM. The effects of T2s are rapid and possibly mediated by their direct interaction with mitochondria. Those of T3 are slower and more prolonged, and at least partly attributable to a modulation of the cellularity of tissues that are metabolically very active.

Adipose Tissue, Brown↗

PubMed1997

Induction of UCP2 mRNA by thyroid hormones in rat heart.

The possible regulation of the expression of uncoupling protein-2 (UCP2) mRNA by thyroid hormones in different tissues was examined in rats. Triiodothyronine (T3) was found to produce an organ-specific enhancement of UCP2 expression in rat tissues. The effect of T3 was markedly observed in heart, whereas a moderate effect was seen in skeletal muscle and no effect in kidney or liver. These results suggest that UCP2 is a protein that may be involved in the nuclear-mediated effect of T3 on resting metabolic rate in the rat.

Animals↗

PubMed1997

Characterization of the binding of 3,3'-di-iodo-L-thyronine to rat liver mitochondria.

The binding of labelled 3,3'-di-iodo-L-thyronine (3,3'-T2) to isolated rat liver mitochondria has been characterized. Specific binding could be detected only in the inner mitochondrial membrane, not in other mitochondrial subfractions. The composition of the incubation medium influenced the binding capacity, the best combination of high specific binding and low non-specific binding being observed in phosphate buffer, pH 6.4. The specific binding of 3,3'-T2 to mitochondria requires low ionic strength: concentrations of K+ and Na+ higher than 10 mmol/l and 0.1 mmol/l respectively resulted in a decreased binding capacity. The optimal calcium ion concentration was in the range 0.01-1.0 mmol/l. Varying magnesium ion, over the range of concentrations used (0.1-100 mmol/l), had no effect. Both ADP and ATP, at over 1 mmol/l, resulted in an inhibition of the specific binding. Incubation with protease resulted in a decrease in specific binding and an increase in non-specific binding, thus indicating the proteic nature of the binding sites. In addition to the above factors in the local environment the thyroid state of the animal might influence the 3,3'-T2-binding capacity. In fact, the thyroid state of the animal seemed not to have an influence on the affinity constant, but it did affect binding capacity.

Adenosine Diphosphate↗

PubMed1996

Calorigenic effect of diiodothyronines in the rat.

1. In hypothyroid rats, we determined the effects of administration of different doses of 3,3',5-triiodo-L-thyronine (T3), 3,3'-diiodo-L-thyronine (3,3'-T2) and 3,5-diiodo-L-thyronine (3,5-T2) ("T2 isomers' refers specifically to these latter two isomers throughout this paper) on resting metabolism (RM) and on the oxidative capacity (measured as cytochrome oxidase activity) of tissues that are metabolically very active. 2. The T2 isomers induced a dose-dependent calorigenic effect when injected I.P. into hypothyroid rats. The increase in RM was already evident at a dose of 2.5 micrograms (100 g body wt)(-1), and the greatest effect was observed at the highest dose, 10 micrograms (100 g body wt)(-1), when RM reached a value not significantly different from that of the euthyroid controls (1.92 +/- 0.08 and 1.93 +/- 0.13 (1 O2) kg(-1) h(-1) for 3,5'-T2, respectively, vs. 2.1 +/- 0.12 (1 O2) kg(-1) h(-1) for euthyroid controls). T3 administration restored RM to normal euthyroid values, even at a dose of 2.5 micrograms (100 g body wt)(-1). 3. The effect of T2 isomers on RM was paralleled by an increase in the oxidative capacity of tissues that are metabolically very active (liver, skeletal muscle, brown adipose tissue (BAT) and heart). The increases were between 33% (liver + 3,3'-T2) and 63% (muscle + 3,3'-T2). By contrast, T3 induced its greatest effect on the liver, with a smaller effect on skeletal muscle, but no significant stimulation in heart and BAT, whatever the dose. 4. These results suggest that T8 isomers might be mediators of the direct thyroid hormone regulation of energy metabolism.

Animals↗

PubMed1996

Biochemical and functional differences in rat liver mitochondrial subpopulations obtained at different gravitational forces.

Previous studies have reported that liver mitochondria may be fractionated into different subpopulations. However, no careful studies have been performed to exclude mitochondrial damage and to investigate more thoroughly the possible biochemical differences existing between the subpopulations. In this study, we analysed the integrity and the biochemical properties of rat liver mitochondria. Mitochondrial fractions were obtained by differential centrifugation at different gravitational forces: 1000 g (M1 fraction), 3000 g (M3 fraction) and 10,000 g (M10 fraction). The integrity of these organelles was checked by measuring citrate synthase activity both in the presence and absence of Triton X-100 detergent. Biochemical analyses included polarographic determination of cytochrome oxidase activity and respiratory parameters and spectrophotometric determination of cytochrome content. (1) The integrity of mitochondria was almost homogeneous between fractions (88.5, 80 and 78.3% in M1, M3 and M10 fractions, respectively). (2) The heaviest M1 fraction contains mitochondria which are on average twice as large as M3 and about three times as large as M10. (3) The M1 fraction exhibited the highest specific cytochrome oxidase activity (1040 +/- 20 n Atoms O/min x mg protein) and the highest respiratory rates (72 +/- 3 n Atoms O/min x mg protein and 526 +/- 45 n Atoms O/min x mg protein for States 4 and 3, respectively). Oxidative capacity and respiratory rates decreased as the size of the organelles decreased, reaching values of 1/5 and 1/14 in the M3 and M10 fractions as compared to the M1. (4) These changes are accompanied by a change in the respiratory control ratio (RCR), which varies from 7.3 in M1 to about 2.0 in M10. A similar trend was observed in cytochrome contents but the differences were not as great as cytochrome oxidase activity and State 3 respiration. These results, as a whole, show that a mitochondrial heterogeneity exists in rat liver cell. We suggest that the above-mentioned differences might represent steps of mitochondrial maturation. The maturation would be fundamentally based on the increase of efficiency of the mechanism for ATP synthesis.

Acid Phosphatase↗

PubMed1996

Demonstration of in vivo metabolic effects of 3,5-di-iodothyronine.

The objective of the present study was to test in vivo the metabolic effects of 3,5-di-iodothyronine (3,5-T2) in unanesthetized and unrestrained male Sprague-Dawley rats. Amino acid and lipid metabolisms were investigated by breath tests using as tracers the 13C-carboxyl-labeled molecules of leucine, alpha-ketoisocaproic acid (KIC) and octanoic acid, in four different groups of rats: hypothyroid animals (receiving propylthiouracil (PTU) and iopanoic acid), hypothyroid animals treated with either a daily i.p. injection of 3,5-T2 (25 micrograms/100 g body weight), or tri-iodothyronine (T3) (1 microgram/100 g body weight), and control euthyroid animals receiving equivalent volumes of the vehicle solutions. Energy expenditure was measured by continuous monitoring of O2 consumption and CO2 production in these different groups. Daily energy expenditure was decreased by 30% in PTU-treated rats. The chronic treatments with 3,5-T2 and T3 restored daily energy expenditure to the control level. 13CO2 recovered in breath following the i.v. injection of octanoic acid-[1-13C] was decreased in hypothyroid animals compared with control animals (P < 0.05) and restored to control values by T3 and 3,5-T2 treatments. The 13CO2 recovered in breath after i.v. injection of leucine-[1-13C] was increased in PTU-treated compared with control animals (P < 0.05). Chronic treatment with either 3,5-T2 or T3 restored 13CO2 to control values. Excretion of 13CO2 recovered in breath following the i.v. injection of KIC-[1-13C] was increased in PTU-treated compared with control animals. Chronic treatments with either 3,5-T2 or T3 did not restore KIC decarboxylation. These results suggest that 3,5-T2 exerts metabolic effects on energy expenditure, on both lipid beta-oxidation and leucine metabolism in hypothyroid rats. We conclude that 3,5-T2 is a metabolically active iodothyronine.

Amino Acids↗

PubMed1995

Relationship between dose, mode of administration and effects of triiodothyronine on two hepatic responsive enzymes.

We have examined serum 3,3',5-triiodo-L-thyronine (T3) levels and the activity of two hepatic responsive enzymes [malic enzyme (ME) and alpha-glycerophosphate dehydrogenase (alpha-GPD)] in the livers of hypothyroid rats, under conditions where different doses of T3 (1 and 2.5 micrograms/100 g b.w.) were administered daily for one week either by intraperitoneal injection or by continuous infusions. In infused animals, serum T3 concentrations were constant for the whole period of treatment while in injected groups, widely oscillating diurnal levels were observed. The injection of 2.5 micrograms/100 g b.w. resulted, at the end of the treatment, in serum T3 levels which were higher than in animals receiving the same dose by infusion. No significant differences were observed when the administered dose was 1 microgram/100 g b.w. The basal levels of alpha-GPD and ME, which were markedly reduced in the livers of hypothyroid rats, were returned to normal both in infused rats (both with the dose of 1 microgram and 2.5 micrograms/100 g b.w. of T3) and in rats injected with a dose of 1 microgram/100 g b.w.). On the other hand, the dose of 2.5 micrograms/100 g b.w. when administered by injection, resulted in alpha-GPD and ME activities which were significantly higher even than those found in normal ones. The results indicate that both the diurnal T3 profile and the activity of the two hepatic T3 responsive enzymes are dependent not only on the dose but also on the administration mode.

Animals↗

PubMed1994

Specific binding sites for 3,3'-diiodo-L-thyronine (3,3'-T2) in rat liver mitochondria.

Specific binding sites for 3,3'-T2 can be detected in swollen and osmotically treated mitochondria (OTM) from normal and hypothyroid rat liver. In hypothyroid animals, maximal values of binding were obtained at 0 degrees C while values were lower at 37 degrees C and no specific binding could be observed at 60 degrees C. Binding was maximal at pH 6.4 and the mean values for the apparent association constant (Ka) and the binding capacity were on average 0.5 x 10(8) M-1 and 2.4 pmol/mg mitochondrial protein, respectively. No differences were observed between normal and hypothyroid rats with the exception of the capacity that was higher in normal animals (5.5 pmol/mg mitochondrial protein). The specificity of 3,3'-T2 binding, examined in competition studies, followed this order: 3,3'-T2 > 3,5-T2 > rT3. The other iodothyronines (3',5'-T2, T3, T4, 3-T1, 3'-T1, 3,5-Diac and 3,3'-Diac) showed only a small competition or none at all.

Animals↗

PubMed1994

Interaction of diiodothyronines with isolated cytochrome c oxidase.

Diiodothyronines (3,3'-T2 and 3,5-T2) stimulate the activity of isolated cytochrome c oxidase (COX) from bovine heart mitochondria. Maximal stimulation of activity (about 50%) is obtained with 3,3'-T2 at pH 6.4 and with 3,5-T2 at pH 7.4. In contrast, 3,5,3'-triiodothyronine (T3) exhibited no or little stimulation of COX activity. Binding of the hormones to COX leads to conformational changes as shown by modified visible spectra of the oxidized enzyme. It is suggested that 'short-term' effects of thyroid hormones on mitochondrial respiration are at least partly due to the allosteric interaction of diiodothyronines with the COX complex.

Animals↗

PubMed1994

Cold exposure induces different uncoupling-protein thermogenin masking/unmasking processes in brown adipose tissue depending on mitochondrial subtypes.

The effect of cold exposure on thermogenic parameters such as mitochondrial protein content, GDP-binding and uncoupling protein (UCP) levels in different mitochondrial fractions from rat brown adipose tissue has been investigated. Rats were exposed from 12 h to 5 days at 4 degrees C, and three mitochondrial fractions were isolated by differential centrifugation: the M1 fraction (1000 g), the M3 fraction (3000 g) and the M15 fraction (15,000 g). Cytochrome c oxidase activity as an index of mitochondrial mass showed an increase during cold exposure. During the first 24 h of cold exposure UCP was incorporated specifically into the M3 and M15 mitochondrial fractions, and thereafter UCP appeared in the heaviest M1 fraction. However, specific GDP binding was increased during the first 24 h in the same way in all subpopulations, and this increase continued up to 72 h of cold exposure. Results suggest that different molecular events are involved during acute and chronic adaptation to cold: during the first 24 h of cold acclimatization, thermogenic activity is increased by an unmasking process of the UCP binding sites in the M1 mitochondrial fraction as UCP levels were constant and GDP binding increased, but in the M3 and M15 fraction the increase in thermogenic activity was completely due to an increase in GDP binding induced by a specific incorporation of UCP targeted to these mitochondria. Thus thermogenic parameters change in a different way in the brown-fat mitochondrial subpopulations during cold acclimatization.

Acclimatization↗

PubMed1994

Activation and inactivation of thyroid hormone by type I iodothyronine deiodinase.

The prohormone thyroxine (T4) is activated by outer ring deiodination (ORD) to 3,3',5-triiodothyronine (T3) and both hormones are degraded by inner ring deiodination (IRD) to 3,3',5'-triiodothyronine (rT3) and 3,3'-diiodothyronine, respectively. Indirect evidence suggests that the type I iodothyronine deiodinase (ID-I) in liver has both ORD and IRD activities, with preference for rT3 and sulfated iodothyronines as substrates. To establish this, we have compared the ORD of rT3 and IRD of T3 and T3 sulfate by homogenates of cells transfected with rat ID-I cDNA and by rat liver microsomes. In both preparations rT3 is the preferred substrate, while deiodination of T3 is markedly accelerated by its sulfation. Kinetic analysis provided similar Km and Vmax values in cell homogenates and liver microsomes. These data demonstrate unequivocally that ID-I is capable of both activating and inactivating thyroid hormone by ORD and IRD, respectively.

Animals↗

PubMed1994

Rapid stimulation in vitro of rat liver cytochrome oxidase activity by 3,5-diiodo-L-thyronine and by 3,3'-diiodo-L-thyronine.

The effect of the iodothyronines (thyroxine (T4), 3,5,3'-triiodo-L-thyronine (L-T3), 3,5-diiodo-L-thyronine (3,5-T2), 3,3'-diiodo-L-thyronine (3,3'-T2), 3',5'-diiodo-L-thyronine (3',5'-T2), 3'-monoiodo-L-thyronine (3'-T1), 3-monoiodo-L-thyronine (3-T1) and thyronine (T0)) on rat liver cytochrome oxidase (COX) activity after their addition to rat liver homogenate and isolated mitochondria from normal and hypothyroid rats has been investigated. The addition of 3,3'-T2 and 3,5-T2 (T2s) to the liver homogenate from hypothyroid rats, but not from normal rats, significantly enhanced COX activity. The addition of T3 had a remarkably lower effect that was almost completely abolished when the propylthiouracil (PTU), an inhibitor of the type I deiodinase activity, was also added to the incubation mixture. After the addition of T2s the maximum effect was obtained at a concentration of about 10(-6) M for both 3,3'-T2 and 3,5-T2, while a 50% increase was obtained at a concentration of about 10(-9) M in both cases. The effects of T2s were rapid and already evident after 5 min of incubation (+40-50%). The maximal effect was reached after only 30 min of incubation. The above effects were not observed after the addition of T2s to the isolated mitochondria. The results clearly demonstrate that both 3,3'-T2 and 3,5-T2 directly stimulate mitochondrial COX activity which is possibly achieved through a cytoplasmic factor. The addition of the other iodothyronines (T4, 3',5'-T2, 3'-T1, 3-T1 and T0).

Animals↗

PubMed1994

Rapid glucuronidation of tri- and tetraiodothyroacetic acid to ester glucuronides in human liver and to ether glucuronides in rat liver.

T3 is the principal bioactive thyroid hormone, although its metabolite 3,3',5-triiodothyroacetic acid (TA3) shows higher affinity for the nuclear T3 receptor. However, TA3 has a low in vivo potency because of its short half-life in both humans and rats. We have compared the glucuronidation of TA3, 3,3',5,5'-tetraiodothyroacetic (TA4), T3, and T4 by human and rat liver microsomes. In rat liver, TA3 and TA4 were glucuronidated about 20 times faster than T3 and T4. Both TA3 and TA4 glucuronides were stable during treatment with dilute base or methanol, suggesting that they represent ether glucuronides with the phenolic hydroxyl group. In human liver, TA3 and TA4 were glucuronidated about 1500 and 200 times faster than T3 and T4, respectively. Both TA3 and TA4 glucuronides were hydrolyzed by treatment for 30 min at 37 C with 0.1 M NaOH and showed transesterification to the methyl esters by treatment with methanol, suggesting that they represent ester glucuronides with the carboxyl group. Therefore, both TA3 and TA4 undergo very rapid, but different, types of glucuronidation in human and rat liver. The high glucuronidation rates may explain their short half-lives and the low bioactivity of TA3 in vivo.

Animals↗

PubMed1994

Effect of thyroid status on the oxidative capacity of Sertoli cells isolated from immature rat testis.

Our previous studies indicate the Sertoli cell as a target for thyroid hormone action at testis level. In the present study we evaluated the effect of thyroid hormone on Sertoli cell oxidative capacity measured by specific cytochrome oxidase (COX) activity and intracellular adenosine triphosphate (ATP) content. Sertoli cells were isolated from 21-day-old rats. Hypothyroidism, induced from the day of birth by administration of 0.025% methimazole, was characterized by a severe delay of body and testis growth and resulted in a lower COX activity (-40%, p < or = 0.01) and a lower ATP content (-35%, p < or = 0.01) by isolated Sertoli cells. Administration of triiodothyronine (10 micrograms/100 g body wt on alternate days) to hypothyroid rats improved body and testis growth and restored both COX activity and ATP content. The presence of high-affinity, low-capacity binding sites for triiodothyronine in Sertoli cell mitochondria also was demonstrated. This study, unlike that carried out on the whole testis from adult rats, demonstrates that thyroid hormone affects the energy metabolism of Sertoli cells from midpubertal rat testes.

Adenosine Triphosphate↗