Stanislav Pavelka

Tissue Metabolism and Plasma Levels of Thyroid Hormones in Critically Ill Very Premature Infants

Thyroid status was characterized in very preterm infants (gestational age≤32 wk; n = 61) from birth through d 14, and in infants who died within 16 d after delivery (n = 10), where it was also correlated with metabolism of iodothyronines in peripheral tissues (brain, liver, kidney, skeletal muscle, and adipose tissue). At 3 d of life, mean plasma levels of thyroxine, triiodothyronine, and TSH started to decrease, being lower in the critically ill compared with healthy premature neonates. Activities of the three iodothyronine deiodinases enzymes (type I, II, and III, respectively) were detected in all postmortem tissue samples, except for absence of the type II activity in kidney. All activities were the highest in liver and differed in other tissues. Lack of correlation between the type I activity in liver(and kidney), and plasma levels of thyroid hormones suggested that the thyroid was the primary source of circulating triiodothyronine. On the other hand, namely in brain, correlations between activity of the deiodinases and plasma hormone levels were found which suggested a complex control by thyroid hormones of their own metabolism. High activity of type III in liver, adipose tissue, and skeletal muscle demonstrated a role of these tissues in thyroid hormones degradation. Results support the view that peripheral tissues of very preterm infants are engaged in local generation of triiodothyronine, and inactivation of thyroid hormones, but do not represent a major source of circulating triiodothyronine.

Type I iodothyronine 5'-deiodinase mRNA and activity is increased in adipose tissue of obese subjects.

Differentiation and metabolism of adipose tissue are modulated by thyroid hormones (THs), but relatively little is known about the metabolism of THs in this tissue. Expression of the genes for type I iodothyronine 5′-deiodinase (D1), leptin (LEP) and stearoyl-CoA desaturase 1 (SCD-1) was evaluated in omental (OM) and subcutaneous (SC) fat using a cohort of 70 humans. Activities of iodothyronine deiodinases (D1, D2 and D3) were assessed in a randomly selected subpopulation of 19 subjects. D1 expression was upregulated in both OM (P=0.011) and SC (P=0.003) fat of obese subjects. Concomitantly, OM (P=0.002) and SC (P=0.028) LEP expression were increased in obesity, associated with both D1 mRNA (r=0.315, P=0.014) and activity (r=0.647, P=0.023) and inversely related to SCD-1 (r=−0.266, P=0.034) expression in SC fat. Also D1 (but not D2 and D3) activity was increased in OM (∼fourfold, P=0.010) and SC (∼eightfold, P=0.004) fat of obese when compared with non-obese subjects and correlated in both OM (r=0.528, P=0.036) and SC (r=0.749, P=0.005) fat with body mass index. Our results document increased D1 gene expression and activity in adipose tissue of obese humans and suggest a role of 3,5,3′-triiodo-L-thyronine formed by D1 in response to leptin in the modulation of adipose tissue metabolism.

Low content of mitochondrial ATPase in brown adipose tissue is the result of post-transcriptional regulation

The mRNA levels of ATPase β, ATPase 6, cytochrome oxidase (COX) VIb and COX I subunits were found to be 2.4–13.8‐fold higher in brown adipose tissue (BAT) than in heart, skeletal muscle, brain and liver of mice. The comparison with tissue contents of ATPase and COX revealed that the selective, 5–11‐fold reduction of ATPase in BAT is not caused by decreased transcription of ATPase genes. Likewise, the ATPase β and COX VIb mRNA levels in cultured brown adipocytes were also not influenced by norepinephrine, which activated the expression of the UCP gene by two orders of magnitude. The results indicate that the biosynthesis of mitochondrial ATPase in BAT is post‐transcriptionally regulated.

Is the mitochondrial dicyclohexylcarbodiimide-reactive protein of Mr 33 000 identical with the phosphate transport protein?

Dicyclohexylcarbodiimide acts at low concentrations as a specific inhibitor of H’-ATPase due to the covalent binding to a hydrophobic subunit of F, [1,2]. In mammalian mitochondria, however, an additional protein of different M, (33 000) is also labelled at H’-ATPase-inhibitor concentrations of [‘4C]DCCD f2-41. In contrast to the DC~D-boding protein of F, it is neither extracted by chloroformmethanol (2: 1, v/v>, nor is it detected in the isolated H’-ATPase complex [3,4]. In different types of mitochondria the 33 000 DCCD-reactive protein is present in a near stoichiometrical quantity with respect to F,, even though mitochondria differ in the natural content of H’-ATPase up to 10 times [5]. Here, we describe the separation of the 33 000 DCCD-reactive protein from the DCCD-binding subunit of F, and its purification. Evidence is presented for its identity with the TV-ethylmaleimide (NEM)-sensitive phosphate~proton symporter of the mitochondrial membrane.

Bromide kinetics and distribution in the rat. I. Biokinetics of 82Br-bromide.

Biological half-lives of bromine in 15 different organs and tissues of the rat, in addition to the whole-body half-life, were determined by measuring the radioactive concentration of 82Br-bromide in samples of tissues collected at the time intervals of 12–396 h from animals that continuously (up to 17 d) received 82Br-labeled bromide in their drinking water. The half-life values, calculated from the experimental data by the method of gradual estimates of the parameters in question with the SPSS statistical program, ranged from 94.3 ± 14.6 h in the thyroid gland to 235.0 ± 88.9 h in liver. In most of the studied tissues, the biological half-lives of bromine were shorter than in the whole body, in which it equaled 197.8 ± 22.2 h. Significant correlation between the values of the steady-state concentration of bromide and of the biological half-life was found for most tissues (except for liver). The steady-state concentrations of 82Br in tissues are probably proportional to the magnitude of bromide space, and, consequently, of chloride space.

High bromide intake affects the accumulation of iodide in the rat thyroid and skin

The effect of a high bromide intake on the kinetics of iodide uptake and elimination in the thyroid and skin of adult male rats was studied. In rats fed a diet with sufficient iodine supply (>25 µg I/d), the iodide accumulation in the skin predominated during the first hours after 131I -iodide application. From this organ, radioiodide was gradually transferred into the thyroid. A high bromide intake (>150 mg Br−/d) in these animals led to a marked decrease in iodide accumulation, especially by the thyroid, because of an increase in iodide elimination both from the thyroid and from the skin. In rats kept under the conditions of iodine deficiency (<1 µ I/d), the iodide accumulation in the thyroid, but not in the skin, was markedly increased as a result of a thyrotropic stimulation. The effect of a high bromide intake (>100 mg Br−/d) in these animals was particularly pronounced because the rates of iodide elimination were most accelerated both from their thyroid and from their skin.

N-3 polyunsaturated fatty acids supplementation does not affect changes of lipid metabolism induced in rats by altered thyroid status.

Epidemiological studies have demonstrated that n-3 polyunsaturated fatty acid (PUFA) consumption is associated with a reduced risk of atherosclerosis and hyperlipidemia. It is well known that lipid metabolism is also influenced by thyroid hormones. The aim of our study was to test whether n-3 PUFA supplementation (200 mg/kg of body weight/day for 6 weeks given intragastrically) would affect lipid metabolism in Lewis male rats with altered thyroid status. Euthyroid, hypothyroid, and hyperthyroid status of experimental groups was well defined by plasma levels of triiodothyronine, the activity of liver mitochondrial glycerol-3-phosphate dehydrogenase, and by relative heart weight. Fasting blood glucose levels were significantly higher in the hyperthyroid compared to the euthyroid and hypothyroid rats (5.0±0.2 vs. 3.7±0.4 and 4.4±0.2 mmol/l, respectively). In hyperthyroid animals, the concentration of plasma postprandial triglycerides was also increased compared to euthyroid and hypothyroid rats (0.9±0.1 vs. 0.5±0.1 and 0.4±0.1 mmol/l, respectively). On the other hand, hypothyroidism compared to euthyroid and hyperthyroid status was associated with elevated plasma levels of total cholesterol (2.6±0.2 vs. 1.5±0.1 and 1.6±0.1 mmol/l, respectively), LDL cholesterol (0.9±0.1 vs. 0.4±0.1 and 0.2±0.1 mmol/l, respectively) as well as HDL cholesterol (1.6±0.1 vs. 1.0±0.1 and 1.3±0.1 mmol/l, respectively). Supplementation of n-3 PUFA in the present study did not significantly modify either relative heart weight or glucose and lipid levels in any thyroid status.

Characterization of sulphydryl groups of the mitochondrial phosphate translocator by a maleimide spin label

A maleimide spin label strongly inhibits the phosphate/H+ symporter of rat liver mitochondria. While inducing half‐maximal inhibition of transport, the spin label reacts preferentially with the SH groups of the carrier, which are at least of two types. One type of SH group is localized close to the surface of the membrane and its environment does not significantly influence the mobility of the probe. The second type of SH group is buried in the membrane, is not accessible to ascorbate or chromium oxalate and its environment greatly restricts the motion of the probe.

Bromide transfer through mother's milk and its impact on the suckling rat.

Effects of a high bromide intake in lactating rats on the performance of the dams and on the prosperity of their young were studied. In the dams, two marked consequences undoubtedly caused by high bromide intake were observed: stagnation in the extent of diet and water consumption in the course of the lactation period, and a conspicuous drop in the production rate of mothers milk. A very high intake of bromide in the mothers in the course of the nursing period (about 220 mg Br−/d per dam) also caused a marked decrease in the body weight increments in their suckling young. Only about one-half of these young survived and their general condition was very poor. It is suggested that one of the possible reasons for the observed marked decrease in the production of mothers milk in dams with high bromide intake could be a decreased stimulation of the mammary glands as a consequence of reduced consumption of mothers milk by the suckling. Bromide ions ingested by the dams easily moved into the rat milk. Via mothers milk, bromide was transferred in a large extent to the suckling. The amount of bromide in mothers milk depended on the bromide concentration in the drinking water taken by the dams. With the addition of 5 g bromide per liter (providing the mean daily bromide dose of 220 mg), bromide ions replaced about 54% of the chloride in the milk. A rise in the concentration of both halogens caused also an increase in the concentration of sodium in mothers milk. The exact mechanism(s) of bromide interference with postnatal developmental processes in the young remain(s) unclear.

Bromide kinetics and distribution in the rat. II. Distribution of bromide in the body.

The distribution of 82Br-bromide in 15 different organs and tissues of rats has been determined by high-resolution γ-ray spectrometry and by the scintillation counting technique at different times after the application of Na 82Br, either by subcutaneous injection or by continuous administration in the drinking water. The amount of 82Br-bromide in the various tissues reached its largest uptake within a few hours, and the concentration ratio of 82Br in the tissues to blood remained practically constant between 8 and 396 h after the application. The whole stomach of rats was the only organ of those investigated that had a larger uptake of 82Br than blood. Contrary to some previous findings, the concentration of radiobromide in the thyroid was found not to exceed that in the blood. A remarkably high concentration of 82Br was found in the skin, which represented, because of its large mass, the most abundant depot of bromide in the body of rats. The demonstrated excretion of bromide was mainly renal, at a rate of approximately 5% of the administered dose per 24 h.