Basal and T3-induced ROS production in lymphocyte mitochondria is increased in type 2 diabetic patients.

Mitochondrial function, including production of reactive oxygen species (ROS), is important in the pathogenesis of diabetes and its complications. Thyroid hormones are major regulator of these processes. Hence, the aim of this study was to examine the thyroid hormone regulation of ROS production in human lymphocytes in patients with diabetes mellitus type 2 (T2DM). Lymphocytes from 10 controls and 10 persons with T2DM were examined. Mitochondrial membrane potential (MMP) was examined by flow cytometry after staining with MitoTracker Green (MTG). Similarly ROS was measured following staining with carboxy-H2DCFDA. MMP was increased in T2DM patients and T3 stimulation increased MMP in controls [1398 a.u. (979-4094) vs. 2156 a.u. (1611-15189), p=0.04, median and quartiles] as well as in T2DM patients [9167 a.u. (7387-11746) vs. 20274 a.u. (17183-27839 p=0.004, median and quartiles]. Basal ROS concentration was increased in lymphocytes from T2DM and T3 significantly stimulated ROS concentration in controls [3691 a.u. (2584-6396) vs. 5650 a.u. (3001-7802) p=0.013, median and quartiles] and in T2DM patients [19271 a.u. (6288-25282) vs. 23178 a.u. (10004-28857) p=0.013, median and quartiles]. The ratio of ROS production related to MMP was significantly higher in T2DM, unstimulated as well as T3-stimulated in T2DM. Unstimulated and T3 stimulated ROS production and MMP were higher in lymphocytes from diabetic patients. An altered balance between ROS production and MMP, favoring ROS production in T2DM patients, was found suggesting that an increased mitochondrial sensitivity for T3 may be a significant factor responsible for increased ROS activity in diabetic patients.

Subclinical hypothyroidism affects mitochondrial function.

The aim of the present study was to examine mitochondrial function in cells from persons with subclinical hypothyroidism and euthyroid controls. The participating persons were examined clinically and had basal oxygen consumption (VO(2)) determined. The concentrations of thyroid hormones and thyrotropine stimulating hormone were determined, and mitochondrial function in isolated mononuclear blood cells was examined by enzymatic methods [citrate synthase activity (CS)] and by flow cytometry (mitochondrial membrane potential by TMRM fluorescence and mitochondrial mass by MTG fluorescence). The ratio of T(4)/T(3) was lowered in subclinical hypothyroidism patients compared to controls (2.5+/-0.5 vs. 2.9+/-0.4, p=0.005). VO(2) was increased in persons with subclinical hypothyroidism compared to controls (adolescents: 134+/-27 ml O(2)/min*m(2) vs. 119+/-27 ml O(2)/min*m(2), p=0.006, adults: 139+/-14 ml O(2)/min*m(2) vs. 121+/-17 ml O(2)/min*m(2), p=0.001). The mitochondrial function, represented by citrate synthase activity, MTG, and TMRM fluorescence were all increased (CS in subclinical hypothyroidism vs. controls: 0.074+/-0.044 nmol/mg*min vs. 0.056+/-0.021 nmol/mg*min, p=0.005; MTG fluorescence in subclinical hypothyroidism vs. controls: 7,482+/-1,733 a.u. vs. 6,391+/-2,171 a.u., p=0.027; TMRM fluorescence in subclinical hypothyroidism vs. controls: 13,449+/-3,807 a.u. vs. 11,733+/-4,473 a.u, p=0.04). Our results indicate an increased mitochondrial stimulation, eventually caused by increased deiodination of T(4) to intracellular bioactive iodothyronines in adults and adolescents with subclinical hypothyroidism.

Measure of expression of mitochondrial related genes in human mononuclear blood cells, adipose white tissue and smooth muscle cells.

BACKGROUND: The role of mitochondrial dysfunction is currently studied intensively, but the cumbersome procedure of obtaining tissue from humans has restricted the number of subjects studied. Therefore, the aim of the present study was to examine the expression of mitochondrial related genes in blood cells from humans and to compare the results with measurements of mitochondrial membrane potential known to be regulated by thyroid hormones. METHODS: In a group of 17 healthy women subscribed for hysterectomy on a benign basis, muscle tissue, fat tissue samples and blood specimens were obtained. Mitochondrial mass and membrane potential was examined in peripheral blood monocytes by flow cytometry. Gene expression of PGC-1alpha, PGC-1beta, NFR-1, NRF-2 and TFAM was determined by real-time PCR. RESULTS: All genes were expressed in the 3 tissues examined, though with different magnitude. Most genes were expressed in mononuclear blood cells at a magnitude comparable to that in white adipose tissue. Furthermore, a significant correlation was observed between PGC-1beta and Mitochondrial Membrane Potential (MMP) and Mitochondrial Mass (MM). CONCLUSION: Measurement of expression of mitochondrial related genes in human mononuclear blood cells may be useful for examining mitochondrial function and regulation by thyroid hormones in humans.

Evidence of mitochondrial dysfunction in obese adolescents.

AIM: Although obesity and weight gain generally are anticipated to be caused by an imbalance between energy intake and energy expenditure, the significance of thyroid hormones (TH) remains unclear. Examination of mitochondrial function may reflect intracellular thyroid hormone effect and elucidate whether a lower metabolic rate is present. METHODS: In a group of 34 obese adolescents (age <16 years and body mass index above the age-related 95th percentile), and an age- and gender-matched group of 32 lean adolescent, thyroid stimulating hormone (TSH) and basal oxygen consumption were measured and mitochondrial function in peripheral blood monocytes was determined by flow cytometry. RESULTS: Significant increase in TSH (3.06 +/- 1.56 mU/L vs. 2.33 +/- 0.91 mU/L, p < 0.05) and a decrease in VO2 (129 +/- 16 mL O2/m(2)*min vs. 146 +/- 15 mL O2/m(2)*min, p < 0.05) were observed in obese adolescents compared with lean adolescents. Flow cytometry analysis demonstrated a lower mitochondrial mass (6385 +/- 1962 a.u. vs. 7608 +/- 2328 a.u., p < 0.05) and mitochondrial membrane potential (11426 +/- 3861 a.u. vs. 14017 +/- 5536 a.u., p < 0.05) in obese adolescents compared with lean adolescents. These results are even more pronounced in adolescents with obese mothers. CONCLUSION: In obese adolescents, the increased TSH and lowered VO2 propose a lowered basal metabolic rate and the impaired mitochondrial function suggests a decreased thyroid hormone stimulation of mitochondrial energy production. The maternal in-heritage is suggestive of a basal metabolic defect or mitochondrial resistance for TH.

Subclinical hyperthyroidism in patients with nodular goiter represents a hypermetabolic state.

The aim of the study was to examine the metabolic status in patients with suppressed TSH but values of FT4I and T3 within the reference range (subclinical hyperthyroidism [sH]). Thirteen patients and 13 control persons with nodular goiter were included. The metabolic state was determined by measurements of basal oxygen consumption (VO2), bone mineral density (BMD), and the circadian variation of TSH. Further was the pituitary thyroid axis examined by studying the effect of lowering thyroid hormones by methimazol treatment. The circadian variation of TSH varied from that of normal persons as the night surge was abolished. The basal VO2 was significantly higher and BMD was significantly lower in patients with sH compared to control persons. Restoration of TSH by lowering of thyroid hormone concentrations lead to a normalization of VO2 and restoration of the circadian variation of TSH. The preserved pituitary thyroid axis, the abolished circadian TSH variation, the increased VO2, and decreased BMD in patients with suppressed TSH, but peripheral thyroid hormone concentrations within the reference range, indicate a hyper metabolic state, which might reflect either an altered cellular set point or an increased sensitivity towards thyroid hormones in peripheral cells and in the thyrotrope cells.

Subclinical hypothyroidism is associated with a low-grade inflammation, increased triglyceride levels and predicts cardiovascular disease in males below 50 years.

OBJECTIVE: Mild thyroid failure is associated with an increased risk for development of atherosclerosis, but whether subclinical hypothyroidism is related to risk for cardiovascular disease is controversial. The purpose of the present study was to examine a possible association between subclinical hypothyroidism and cardiovascular disease. DESIGN: Cross-sectional study of a general population. PATIENTS: Twelve hundred and twelve subjects, men and women, between 20 and 69 years old without thyroid disease not treated with drugs interfering with thyroid function or analysis of TSH were included. MEASUREMENTS: Clinical signs of cardiovascular disease based on a questionnaire and medical records and laboratory analysis of lipids, atherothrombotic risk markers, C-reactive protein and TSH. RESULTS: The main findings were a high incidence of subclinical hypothyroidism (19.7%) in a general population. Subclinical hypothyroidism was associated with higher concentrations of triglycerides and C-reactive protein. Below 50 years of age cardiovascular disease was more frequent in males with subclinical hypothyroidism compared to euthyroid males. Subclinical hypothyroidism was a predictor of cardiovascular disease in males below 50 years with an odds ratio of 3.4 (95% confidence interval 1.6-6.8) for developing cardiovascular disease compared to euthyroid age-matched males. CONCLUSION: Our study demonstrates that patients with subclinical hypothyroidism have increased levels of triglycerides and signs of low-grade inflammation (raised C-reactive protein levels) and that subclinical hypothyroidism might be a risk factor for development of cardiovascular disease in younger males.

Randomized placebo-controlled trial of perindopril in normotensive, normoalbuminuric patients with type 1 diabetes mellitus.

Diabetic nephropathy is one of the leading causes of end-stage renal disease. We examined whether ACE inhibitor treatment may have a nephroprotective effect in normotensive insulin-dependent diabetic patients without microalbuminuria and with normal glomerular filtration rate (GFR), and whether any effect was associated with the ACE genotype. In a prospective double-blind randomized study, normotensive patients with type 1 diabetes mellitus with normal serum creatinine and no microalbuminuria were treated with either placebo or perindopril, an ACE inhibitor. Urine albumine/creatinine ratio (ACR), mean blood pressure (MBP) and index of glomerular filtration rate (GFR) based on S-creatinine were determined. ACE genotype was determined by electrophoresis. ACR was higher in the placebo group than in the perindopril group after 4 months, and continued to increase during the study period. After 36 months of observation, ACR in the placebo group was 1.7+/-1.1 mg/mmol, and 0.6+/-0.2 mg/mmol in the ACE-inhibitor-treated group (p<0.001, Mann-Whitney test). During treatment, a significant increase in ACR in the placebo group (p=0.007), Wilcoxon matched paired test) was observed. There were no differences between the groups regarding MBP or GFR. The nephroprotective effects of ACE inhibitor treatment was not associated with the ACE genotype (II, ID, DD).

Results from screening for gestational diabetes mellitus in a Danish county.

OBJECTIVE: To examine the complications in gestational diabetes mellitus with special reference to the significance of the threshold for the oral glucose tolerance test (OGTT, plasma glucose > or = 7.8 mmol/l (equivalent to blood glucose 6.9 mmol/l) (WHO criteria) or blood glucose > 6.7 mmol/l (local criteria) after 2 h 75 g oral glucose load). DESIGN: Prospective descriptive study. SETTING: From April 1, 1995 to April 1, 1997 a screening for gestational diabetes mellitus (GDM) according to the recommendations from the Danish board of health was performed in Ribe county. SUBJECTS: Pregnant women in Ribe county (n = 6158). MAIN OUTCOME MEASURES: Complications during pregnancy and the outcome. RESULTS: Two hundred and twenty (3.6%) women had GDM by the local selection criteria and 2.8% according to the WHO criteria. The study revealed a significantly increased frequency of malformations (7.3% vs. 1.2%, p < 0.0001) and preeclampsia (15.5% vs. 1%, p < 0.0001) in the group with GDM independent of selection criteria (obesity vs. family history and glucosuria). The frequency of preeclampsia appeared higher in the group with obesity (p = 0.040). Malformations appeared with identical frequency in the groups with OGGT threshold higher than blood glucose 6.9 mmol/l (plasma glucose 7.8 mmol/l) (WHO criteria) and with blood glucose between 6.7 and 6.9 mmol/l, whereas preeclampsia did not occur with higher frequency in the latter group. CONCLUSION: Complications appear frequently in women with an abnormal OGGT, and obesity predisposes to preeclampsia. The use of the WHO criteria for screening for GDM would miss a number of women with complications.

Sarcoidosis causes abnormal seasonal variation in 1,25-dihydroxy-cholecalciferol.

OBJECTIVES: The spontaneous seasonal variations in the calcium regulating hormones 1,25-dihydroxy-cholecalciferol (1,25-DHCC) and parathyroid hormone (PTH) were investigated in patients with sarcoidosis. DESIGN: Controlled, prospective observational study with measurements in the winter and summer seasons, respectively. SUBJECTS: Twelve patients (age: median 33, range 21-54 years) with biopsy-verified (n = 8) sarcoidosis were included as well as 11 age-matched healthy control subjects. MAIN OUTCOME MEASURES: Serum values of calcium, ionized calcium, phosphate, chloride, bicarbonate, creatinine, albumin, angiotensin-converting enzyme, alkaline phosphatase, 1,25-DHCC, and PTH. Also, 24-h whole body retention of 99mTc methylene-diphosphonate was assessed. RESULTS: The patient group showed an increased level of 1,25-DHCC in the summer season (w:146 +/- 67, s:198 +/- 73 pmol L-1; P < 0.01) in contrast to the opposite finding among controls (w:161 +/- 34, s:144 +/- 43 pmol L-1; P < 0.05). Comparing the individual seasonal changes between the two groups, the difference was marked (P < 0.001). Compared with controls, total serum calcium was elevated in the summer season in the patient group (P < 0.05), in which the same parameter correlated positively with 1,25-DHCC (r = 0.658; P < 0.01). PTH was increased two to three times above the control values throughout the year (patients: w:0.37 +/- 0.13, s:0.24 +/- 0.08 micrograms L-1; controls: w:0.14 +/- 0.09, s:0.10 +/- 0.04 micrograms L-1; P < 0.001); although, the level of this hormone was still found within the reference interval. 24-h whole body bone scintigraphy failed to show any seasonal variation in bone metabolism. In contrast, serum alkaline phosphatase was found to be increased during the summer season compared with the control group (P < 0.001). Angiotensin-converting enzyme showed no seasonal variation. CONCLUSIONS: In sarcoidosis, 1,25-DHCC is abnormally regulated throughout the year, with a significantly higher serum level in the summer season. Uncontrolled production of 1,25-DHCC in sarcoid pulmonary alveolary macrophages is possibly responsible for hypercalcaemic episodes, and this parameter should be used as a marker of disease activity.

Severe hypothyroidism masquerading as renal impairment.

A case of severe hypothyroidism in a 51-year old male is presented. The patient was especially complaining of weakness, stiffness and moderate pain in the proximal muscle groups together with rhinorrhea and nasal stenosis. Because of severely elevated S-creatine-kinase combined with reduced creatinine clearance and proteinuria, polymyositis with secondary glomerulopathy was suspected. Meanwhile, biopsies from skin, muscle, and kidney were normal. All symptoms disappeared 3 months after thyroid replacement therapy was initiated. S-TSH should be considered when evaluating patients with renal impairment of unknown etiology.

[Peripheral thyroid hormone resistance]. / Perifer thyreoideahormonresistens.

Peripheral thyroid hormone resistance (PTHR) was first described by Refetoff in 1967, and was characterized by raised serum hormone values of T4 and T3 and in appropriately elevated values of TSH. PTHR has been shown to be caused by a mutation in the TR beta gene resulting in impaired nuclear binding of thyroid hormones or an impaired post receptor hormone effect. The patients are often characterized phenotypically by impairment of bone, heart or cerebral function.

Relation between phenotype and intra-cellular thyroid hormone effect in patients with altered peripheral thyroid hormone sensitivity.

OBJECTIVE: We wished to ascertain whether different phenotypic appearances in patients with altered cellular sensitivity to thyroid hormones were related to the type of altered intra-cellular thyroid hormone effect. DESIGN: Blood samples were obtained from two members of a family suffering from generalized thyroid hormone resistance (GTHR) for hormone assays and examination of the cellular thyroid hormone effect, and the results compared with results from other families with signs of altered peripheral thyroid hormone sensitivity. PATIENTS: Two members of a family with thyroid hormone resistance and nine normal persons were studied. MEASUREMENTS: Basal thyroid hormone function tests were measured. The thyroid hormone effect on mononuclear blood cells was determined by measuring the thyroid hormone stimulated oxygen consumption and glucose uptake. RESULTS: The two family members appeared phenotypically normal except for nodular goitre. Thyroid hormone stimulated glucose uptake was depressed whereas thyroid hormone stimulated oxygen consumption was normal. CONCLUSION: Comparison of the present results of the cellular examination in two patients with GTHR, with the results obtained in other families with altered peripheral thyroid hormone sensitivity, suggest that the classic GTHR (phenotype: normal or with goitre) is linked to impaired thyroid hormone stimulated glucose uptake, whereas in patients with osteopetrosis, the thyroid hormone insensitivity seems located at the mitochondrial level (impaired thyroid hormone stimulated oxygen consumption.

3,5-T2 stimulates oxygen consumption, but not glucose uptake in human mononuclear blood cells.

L-thyroxine (T4), L-triiodothyronine (T3) and 3,5-di-iodothyronine (T2) rapidly (within 30 min) stimulated oxygen consumption in human mononuclear blood cells, whereas the D isomers of T4 and T3 and Triac had no stimulatory effect. Oxygen consumption was stimulated by the same magnitude by equimolar concentrations (5-500 nmol/l) of L-T4, L-T3 and 3,5-T2 reaching a plateau at 100 nmol/l of 0.025 umol/mg DNA x h. The stimulatory effects of T4 and T3, but not of T2 were inhibited by PTU. Glucose uptake was stimulated only by L-T4 and L-T3, whereas 3,5-T2, Triac and the D-isomers of T4 and T3 had no effect. The dose response curve reached an apparent maximum at 100 nmol/l of 0.30 mmol/l x mg DNA x h and PTU had no effect on iodothyronine stimulated glucose uptake. We conclude that 3,5-T2 is a significant intracellular stimulator of oxygen consumption, whereas T3 and T4 stimulate glucose uptake.

Triiodothyronine (T3)-associated upregulation and downregulation of nuclear T3 binding in the human fibroblast cell (MRC-5)--stimulation of malic enzyme, glucose-6-phosphate-dehydrogenase, and 6-phosphogluconate-dehydrogenase by insulin, but not by T3.

The specific nuclear binding of triiodothyronine (T3) (NBT3) and the activity of malic enzyme (ME), glucose-6-phosphate-dehydrogenase (G6PD), and 6-phosphogluconate-dehydrogenase (6PGD) were studied in the human fibroblast cell (MRC-5). The overall apparent binding affinity (Ka) was 2.7 x 10(9) L.mol-1 estimated from kinetic studies of nuclear T3 binding, and 2.5 x 10(9) L.mol-1 estimated from equilibrium studies. The scatchard plots were curvilinear and composed of a high-affinity binding site with Ka1 3.4 +/- 0.7 x 10(9) L.mol-1 and maximal binding capacity (MBC) MBC1 57.0 +/- 11.9 fmol/mg DNA and a low-affinity binding site with Ka2 2.9 +/- 1.1 x 10(8) L.mol-1 and MBC2 124.7 +/- 22.1 fmol/mg DNA (n = 6). Incubation of cells with 6 nmol/L T3 for 20 hours reduced NBT3 to 62.2% +/- 15.7% (P less than .01, n = 11). The Ka estimated from kinetic studies was reduced to 6.7 x 10(7) L.mol-1, and the scatchard plots were linear, with Ka 4.5 +/- 1.6 x 10(8) L.mol-1 and MBC 137.0 +/- 44.6 fmol/mg DNA (n = 3) of the same magnitude as the low-affinity binding site in cells incubated without T3 (NS). The reduction in NBT3 was reversible and maximal at T3 concentrations saturating the high-affinity binding site and more than 58% of the total nuclear binding sites. The MRC-5 cell cytosol contained ME, G6PD, and 6PGD activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of nuclear T3 binding by T3 in a human hepatocyte cell-line (Chang-liver) - T3 stimulation of cell growth but not of malic enzyme, glucose-6-phosphatdehydrogenase or 6-phosphogluconate-dehydrogenase.

UNLABELLED: The T3 modulation of nuclear T3 binding (NBT3), the T3 effect on cell growth, and the T3 and insulin effects on malic enzyme (ME), glucose-6-phosphat-dehydrogenase (G6PD) and 6-phosphogluconat-dehydrogenase (G6PD) were studied in a human hepatocyte cell-line (Chang-liver). T3 was bound to a high affinity site with (mean +/- SD, n = 7) Ka1 3.0 +/- 0.3 * 10(9) M-1 and maximal binding capacity (MBC1 112.1 +/- 20.7 fmol/mg DNA, and to a low affinity site with (median, (range), n = 7) Ka2 1.4 (0.6 - 2.6) * 10(7) M-1 and MBC2 766 (461-2687) fmol/mg DNA. Incubation of cells with T3 6 nmol/l for 20 hours reduced the area under the T3 binding curves (AUC) to 80.9% +/- 10.0% of AUC in cells incubated without T3 (p < 0.01, n = 7). The downregulation, being reversible and associated with receptor saturation, was caused by a reduction in MBC1 of the high affinity site to 66.6 fmol/mg DNA, whereas Ka1 was unchanged. T3 stimulated cell growth (p < 0.05, n = 8), but had no effect on the activities of ME, G6PD, and 6PGD. Insulin (1 mumol/l) enhanced the activities of ME (p < 0.01, n = 6) and 6PGD (p < 0.05, n = 6). IN CONCLUSION: The cellular effects of T3 in the human hepatocyte cell-line was: 1) a reversible modulation of NBT3 associated to receptor saturation; 2) stimulation of cell growth; 3) contrary to the findings in rat hepatocytes no stimulation of ME, G6PD or 6PGD. Insulin enhanced ME and 6PGD.

Increased nuclear tri-iodothyronine binding and thyroid hormone-stimulated glucose consumption in mononuclear blood cells from patients with liver cirrhosis.

Nuclear tri-iodothyronine (T3) maximal binding capacity (MBC) and thyroxine- and T3-stimulated cellular oxygen consumption and glucose consumption were examined in mononuclear blood cells from six patients with liver cirrhosis (LC), in six patients with alcoholic hepatitis (AH), and in six healthy control subjects. Serum T3 was decreased in patients with LC. The MBC of T3 was increased significantly (P less than 0.05) in cells from patients with LC compared with patients with AH and controls, whereas the equilibrium association constants did not differ. Unstimulated glucose consumption was slightly increased (P less than 0.05) in cells from patients with AH and LC compared with controls. Thyroid hormone-stimulated glucose consumption was significantly (P less than 0.05) increased in cells from patients with LC compared with controls and patients with AH. Unstimulated oxygen consumption did not differ between the groups, but thyroid hormone-stimulated oxygen consumption was depressed in cells from patients with AC (P less than 0.05) compared with patients with LC and with controls. We conclude that both thyroid hormone-stimulated glucose consumption and T3 nuclear receptor binding in cells from patients with LC are increased, and suggest that the observed changes are responsible for maintenance of euthyroidism in the face of reduced circulating T3.

Decreased thyroid hormone-stimulated oxygen consumption and glucose uptake in mononuclear blood cells from patients with autosomal dominant osteopetrosis type I.

Nine patients, from four different families, with autosomal dominant osteopetrosis were investigated. They all had roentgenological type I disease, characterized by universal, symmetrical osteosclerosis and enlarged thickness of the cranial vault. All patients appeared clinically euthyroid. Thyroxine (T4) and tri-iodothyronine (T3) induced oxygen consumption and glucose uptake were studied in vitro in mononuclear blood cells from patients and control persons. Unstimulated oxygen consumption from patients and controls did not differ, and no difference in unstimulated glucose uptake was observed. The increase in T4 and T3 stimulated oxygen consumption was significantly lower in cells from patients with osteopetrosis (T4: 0.007 +/- 0.004 mumol/mg DNA per h, T3: 0.011 +/- 0.004 mumol/mg DNA per h) compared with controls (T4: 0.017 +/- 0.003 mumol/mg DNA per h, T3: 0.023 +/- -0.013 mumol/mg DNA per h; p less than 0.05, p less than 0.05). Cellular glucose uptake after T4 and T3 stimulation was significantly lower in patients (T4: 0.032 +/- 0.017 mmol/l per mg DNA per h, T3: 0.02 +/- 0.017 mmol/l per mg DNA per h) compared with controls (T4: 0.09 +/- 0.017 mmol/l per mg DNA per h, T3: 0.08 +/- 0.01 mmol/l per mg DNA per h; p less than 0.05, p less than 0.01). The reduced oxygen consumption and glucose uptake indicate thyroid hormone resistance which may be of pathogenetic importance for the development of autosomal dominant osteopetrosis type I.

Effect of selective blockade of oxygen consumption, glucose transport, and Ca2+ influx on thyroxine action in human mononuclear cells.

The effect of selective blockade of cellular glucose transporters, Ca2+ influx, and mitochondrial oxygen consumption on thyroxine (T4)-stimulated oxygen consumption and glucose uptake was examined in human mononuclear blood cells. Blockade of glucose transporters by cytochalasin B (1 x 10(-5) mol/L) and of Ca2+ influx by alprenolol (1 x 10(-5) mol/L) and verapamil (4 x 10(-4) mol/L) inhibited T4-activated glucose uptaken and reduced T4-stimulated oxygen consumption by 20%. Uncoupling of mitochondrial oxygen consumption by azide (1 x 10(-3) mol/L) inhibited T4-stimulated oxygen consumption, but had no effect on glucose uptake. We conclude that T4-stimulated glucose uptake in human mononuclear blood cells is dependent on intact glucose transporters and Ca2+ influx, but not on mitochondrial oxygen consumption. However, oxygen consumption is, in part, dependent on intact glucose uptake.