AJP - Endocrinology and Metabolism

Golden, Kish L.; Marsh, James D.; Jiang, Yang; Brown, Tiane; Moulden, Jerome

doi: 10.1152/ajpendo.00054.2003pmid: 12684218

Sex-related differences in cardiac function have been well documented. The extent to which sex hormones are responsible for these differences is unclear. The current study was designed to determine whether castration and androgen replacement resulted in changes in functional expression of genes encoding the L-type calcium channel and Na/Ca exchanger in isolated rat ventricular myocytes. Sixteen weeks of castration produced a 50% decline in dihydropyridine receptor expression levels and a 16% ( P < 0.05) increase in time to peak shortening. Furthermore, cardiac myocytes isolated from castrated animals also displayed an 18% ( P < 0.001) increase in time to relengthening and an 80% decrease in Na/Ca exchanger gene expression when compared with intact controls. Testosterone treatment of castrated animals completely reversed these effects. These results provide the first evidence that androgens regulate functional expression of the L-type calcium channel and the Na/Ca exchanger in isolated rat ventricular myocytes and thus may play a role in modulating cardiac performance in males and thereby contribute to the observed gender differences in cardiac function. cardiac myocyte; castration; testosterone; calcium channel; sodium/calcium exchanger Address for reprint requests and other correspondence: K. L. Golden, Wayne State Univ. School of Medicine, 421 E. Canfield Ave., Detroit, MI 48201 (E-mail: [email protected] ).

Bakker, Astrid D.; Joldersma, Manon; Klein-Nulend, Jenneke; Burger, Elisabeth H.

doi: 10.1152/ajpendo.00501.2002pmid: 12746215

Parathyroid hormone (PTH) and mechanical stress both stimulate bone formation but have opposite effects on bone resorption. PTH increased loading-induced bone formation in a rat model, suggesting that there is an interaction of these stimuli, possibly at the cellular level. To investigate whether PTH can modulate mechanotransduction by bone cells, we examined the effect of 10 - 9 M human PTH-(1-34) on fluid flow-induced prostaglandin E 2 (PGE 2 ) and nitric oxide (NO) production by primary mouse osteoblastic cells in vitro. Mechanical stress applied by means of a pulsating fluid flow (PFF; 0.6 ± 0.3 Pa at 5 Hz) stimulated both NO and PGE 2 production twofold. In the absence of stress, PTH also caused a twofold increase in PGE 2 production, but NO release was not affected and remained low. Simultaneous application of PFF and PTH nullified the stimulating effect of PFF on NO production, whereas PGE 2 production was again stimulated only twofold. Treatment with PTH alone reduced NO synthase (NOS) enzyme activity to undetectable levels. We speculate that PTH prevents stress-induced NO production via the inhibition of NOS, which will also inhibit the NO-mediated upregulation of PGE 2 by stress, leaving only the NO-independent PGE 2 upregulation by PTH. These results suggest that mechanical loading and PTH interact at the level of mechanotransduction. parathyroid hormone; prostaglandin E 2 ; nitric oxide synthase Address for reprint requests and other correspondence: J. Klein-Nulend, ACTA-Vrije Universiteit, Dept. of Oral Cell Biology, Van der Boechorststraat 7, NL-1081BT Amsterdam, The Netherlands (E-mail: [email protected] ).

Piloquet, H.; Ferchaud-Roucher, V.; Duengler, F.; Zair, Y.; Maugere, P.; Krempf, M.

doi: 10.1152/ajpendo.00042.2003pmid: 12773304

Acetate metabolism was studied in patients with insulin resistance. To evaluate the interaction between glucose and acetate metabolism, we measured acetate and glucose turnover with a hyperinsulinemic euglycemic clamp (hot clamp) in obese and diabetic patients with insulin resistance ( n = 8) and in a control group with normal insulin sensitivity ( n = 6). At baseline, acetate turnover and plasma concentrations were similar between the two groups (group means: 4.3 ± 0.4 µmol · kg - 1 · min - 1 and 128.2 ± 11.1 µmol/l). Acetate concentrations decreased in both groups with hyperinsulinemia but were significantly lower in the insulin-resistant group (20% vs. 12%, P < 0.05). After the hot clamp treatment, acetate turnover increased for the two groups and was higher in the group with normal insulin sensitivity: 8.1 ± 0.7 vs. 5.5 ± 0.5 µmol · kg - 1 · min - 1 ( P < 0.001). No change related to insulin action was observed in either group in the percentage of acetate oxidation. This was ≈70% of overall utilization at baseline and during the clamp. No correlation between glucose and acetate utilization was observed. Our results support the hypothesis that, like glucose metabolism, acetate metabolism is sensitive to insulin. stable isotopes; turnover; insulin resistance; hot clamp Address for reprint requests and other correspondence: M. Krempf, Clinique d'Endocrinologie-Nutrition, Hôtel-Dieu, 44093 Nantes 01, France (E-mail: [email protected] ).

Zhang, Lei; Wheatley, Catherine M.; Richards, Stephen M.; Barrett, Eugene J.; Clark, Michael G.; Rattigan, Stephen

doi: 10.1152/ajpendo.00119.2003pmid: 12759220

TNF-α is elevated in many states of insulin resistance, and acutely administered TNF-α in vivo inhibits insulin-mediated hemodynamic effects and glucose uptake in muscle. In this study, we assess whether the inhibitory effects of TNF-α are affected by insulin dose or muscle contraction. Whole body glucose infusion rate (GIR), femoral blood flow (FBF), hindleg vascular resistance, hindleg glucose uptake (HGU), 2-deoxyglucose uptake into muscles of the lower leg (R'g) and hindleg metabolism of infused 1-methylxanthine (1-MX), a measure of capillary recruitment, were determined. Three groups were studied with and without infusion of TNF-α: euglycemic insulin-clamped, one-leg field-stimulated (2 Hz, 0.1 ms at 30 V), and saline-infused control anesthetized rats. Insulin infusions were 3, 10, or 30 mU · kg - 1 · min - 1 for 2 h. 1-MX metabolism was maximally increased by all three doses of insulin. GIR, HGU, and R'g were maximal at 10 mU and FBF was maximal at 30 mU of insulin. Contraction increased FBF, HGU, and 1-MX. TNF-α (0.5 µg · kg - 1 · h - 1 ) totally blocked the 3 and 10 mU insulin-mediated increases in FBF and 1-MX, and partly blocked GIR, HGU, and R'g. None of the increases due to twitch contraction was affected by TNF-α, and only the increase in FBF due to 30 mU of insulin was partly affected. We conclude that muscle capillary recruitment and glucose uptake due to high levels of insulin or muscle contraction under twitch stimuli at 2 Hz are resistant to TNF-α. These findings may have implications for ameliorating muscle insulin resistance resulting from increased plasma TNF-α and for the differing mechanisms by which contraction and insulin recruit capillary flow in muscle. tumor necrosis factor-α; diabetes mellitus; blood flow; muscles; inflammation; capillaries Address for reprint requests and other correspondence: S. Rattigan, Dept. of Biochemistry, Medical School, Univ. of Tasmania, Private Bag 58, Hobart, 7001, Australia (E-mail: [email protected] ).

Rachdaoui, Nadia; Nagy, Laura E.

doi: 10.1152/ajpendo.00160.2003pmid: 12773307

Tumor necrosis factor-α (TNF-α) is a potent inducer of insulin resistance, and increased TNF-α expression is associated with impaired glucose disposal. Although insulin is the primary regulator of glucose transport in adipose, endothelin-1, a vasoconstrictor peptide that signals through the heterotrimeric G proteins Gα q/11 , potently stimulates glucose uptake in 3T3-L1 adipocytes by a mechanism independent of phosphatidylinositol (PI) 3-kinase. Here, we report that exposure of 3T3-L1 adipocytes to TNF-α for 48 h dose-dependently decreased endothelin-1-stimulated glucose uptake and translocation of GLUT4 to the plasma membrane. TNF-α exposure had no effect on endothelin-1 receptor number at the cell surface. In contrast, TNF-α treatment reduced the quantity of Gα q/11 and proline-rich tyrosine kinase 2 (PYK2) and decreased endothelin-1-stimulated PYK2-Tyr 402 tyrosine phosphorylation. Taken together, these results suggest that TNF-α-induced desensitization of endothelin-1-stimulated GLUT4 translocation and glucose uptake in 3T3-L1 adipocytes is due, at least in part, to a decreased expression of Gα q/11 , leading to a suppression in tyrosine phosphorylation of PYK2. adipocytes; glucose homeostasis; G protein-coupled receptors; Gα q/11 ; proline-rich tyrosine kinase 2 Address for reprint requests and other correspondence: L. E. Nagy, Dept. of Nutrition, Case Western Reserve University, 2123 Abington Rd., Rm. 201, Cleveland, OH 44106-4906 (E-mail: [email protected] ).

Wang, Yuxiang; Tonouchi, Mio; Miskovic, Dragana; Hatta, Hideo; Bonen, Arend

doi: 10.1152/ajpendo.00069.2003pmid: 12900382

Triiodothyronine (T 3 ) regulates the expression of genes involved in muscle metabolism. Therefore, we examined the effects of a 7-day T 3 treatment on the monocarboxylate transporters (MCT)1 and MCT4 in heart and in red (RG) and white gastrocnemius muscle (WG). We also examined rates of lactate transport into giant sarcolemmal vesicles and the plasmalemmal MCT1 and MCT4 in these vesicles. Ingestion of T 3 markedly increased circulating serum T 3 ( P < 0.05) and reduced weight gain ( P < 0.05). T 3 upregulated MCT1 mRNA (RG +77, WG +49, heart +114%, P < 0.05) and MCT4 mRNA (RG +300, WG +40%). However, only MCT4 protein expression was increased (RG +43, WG +49%), not MCT1 protein expression. No changes in MCT1 protein were observed in any tissue. T 3 treatment doubled the rate of lactate transport when vesicles were exposed to 1 mM lactate ( P < 0.05). However, plasmalemmal MCT4 was only modestly increased (+13%, P < 0.05). We conclude that T 3 1 ) regulates MCT4, but not MCT1, protein expression and 2 ) increases lactate transport rates. This latter effect is difficult to explain by the modest changes in plasmalemmal MCT4. We speculate that either the activity of sarcolemmal MCTs has been altered or else other MCTs in muscle may have been upregulated. giant vesicles; heart; monocarboxylate transporter 1 mRNA; monocarboxylate transporter 4 mRNA; monocarboxylate transporter 1 protein; monocarboxylate transporter 4 protein Address for reprint requests and other correspondence: A. Bonen, Dept. of Human Biology and Nutritional Sciences, Univ. of Guelph, Guelph, ON, Canada N1G 2W1 (E-mail: [email protected] ).

Sun, Xiaoyan; Wray, Curtis; Tian, Xintian; Hasselgren, Per-Olof; Lu, James

doi: 10.1152/ajpendo.00446.2002pmid: 12721157

Uncoupling protein 3 (UCP3) is a member of the mitochondrial transporter superfamily that is expressed primarily in skeletal muscle. UCP3 is upregulated in various conditions characterized by skeletal muscle atrophy, including hyperthyroidism, fasting, denervation, diabetes, cancer, lipopolysaccharide (LPS), and treatment with glucocorticoids (GCs). The influence of sepsis, another condition characterized by muscle cachexia, on UCP3 expression and activity is not known. We examined UCP3 gene and protein expression in skeletal muscles from rats after cecal ligation and puncture and from sham-operated control rats. Sepsis resulted in a two- to threefold increase in both mRNA and protein levels of UCP3 in skeletal muscle. Treatment of rats with the glucocorticoid receptor antagonist RU-38486 prevented the sepsis-induced increase in gene and protein expression of UCP3. The UCP3 mRNA and protein levels were increased 2.4- to 3.6-fold when incubated muscles from normal rats were treated with dexamethasone (DEX) and/or free fatty acids (FFA ) ex vivo. In addition, UCP3 mRNA and protein levels were significantly increased in normal rat muscles in vivo with treatment of either DEX or FFA. The results suggest that sepsis upregulates the gene and protein expression of UCP3 in skeletal muscle, which may at least in part be mediated by GCs and FFA. cachexia; glucocorticoids; free fatty acids Address for reprint requests and other correspondence: X. Sun, Dept. of Surgery, Univ. of Cincinnati, 231 Albert Sabin Way, Mail Location 0558, Cincinnati, Ohio 45267-0558 (E-mail: [email protected] ).

Kester, Monique H. A.; Kaptein, Ellen; Roest, Thirza J.; van Dijk, Caren H.; Tibboel, Dick; Meinl, Walter; Glatt, Hansruedi; Coughtrie, Michael W. H.; Visser, Theo J.

doi: 10.1152/ajpendo.00046.2003pmid: 12773305

Sulfation appears to be an important pathway for the reversible inactivation of thyroid hormone during fetal development. The rat is an often used animal model to study the regulation of fetal thyroid hormone status. The present study was done to determine which sulfotransferases (SULTs) are important for iodothyronine sulfation in the rat, using radioactive T 4 , T 3 , rT 3 , and 3,3'-T 2 as substrates, 3'-phosphoadenosine-5'-phosphosulfate (PAPS) as cofactor, and rat liver, kidney and brain cytosol, and recombinant rat SULT1A1, -1B1, -1C1, -1E1, -2A1, -2A2, and -2A3 as enzymes. Recombinant rat SULT1A1, -1E1, -2A1, -2A2, and -2A3 failed to catalyze iodothyronine sulfation. For all tissue SULTs and for rSULT1B1 and rSULT1C1, 3,3'-T 2 was by far the preferred substrate. Apparent K m values for 3,3'-T 2 amounted to 1.9 µM in male liver, 4.4 µM in female liver, 0.76 µM in male kidney, 0.23 µM in male brain, 7.7 µM for SULT1B1, and 0.62 µM for SULT1C1, whereas apparent K m values for PAPS showed less variation (2.0-6.9 µM). Sulfation of 3,3'-T 2 was inhibited dose dependently by other iodothyronines, with similar structure-activity relationships for most enzymes except for the SULT activity in rat brain. The apparent K m values of 3,3'-T 2 in liver cytosol were between those determined for SULT1B1 and -1C1, supporting the importance of these enzymes for the sulfation of iodothyronines in rat liver, with a greater contribution of SULT1C1 in male than in female rat liver. The results further suggest that rSULT1C1 also contributes to iodothyronine sulfation in rat kidney, whereas other, yet-unidentified forms appear more important for the sulfation of thyroid hormone in rat brain. thyroid hormone; sulfation; rat sulfotransferase 1B1; rat sulfotransferase 1C1 Address for reprint requests and other correspondence: T. J. Visser, Dept. of Internal Medicine, Erasmus Medical Center, Rm. Ee 502, Dr Molewaterplein 50, 3015 GE Rotterdam, The Netherlands (E-mail address: [email protected] ).

Bruun, Jens M.; Lihn, Aina S.; Verdich, Camilla; Pedersen, Steen B.; Toubro, Søren; Astrup, Arne; Richelsen, Bjørn

doi: 10.1152/ajpendo.00110.2003pmid: 12736161

Adiponectin is an adipose tissue-specific protein that is abundantly present in the circulation and suggested to be involved in insulin sensitivity and development of atherosclerosis. Because cytokines are suggested to regulate adiponectin, the aim of the present study was to investigate the interaction between adiponectin and three adipose tissue-derived cytokines (IL-6, IL-8, and TNF-α). The study was divided into three substudies as follows: 1 ) plasma adiponectin and mRNA levels in adipose tissue biopsies from obese subjects mean body mass index (BMI): 39.7 kg/m 2 , n = 6 before and after weight loss; 2 ) plasma adiponectin in obese men (mean BMI: 38.7 kg/m 2 , n = 19) compared with lean men (mean BMI: 23.4 kg/m 2 , n = 10) before and after weight loss; and 3 ) in vitro direct effects of IL-6, IL-8, and TNF-α on adiponectin mRNA levels in adipose tissue cultures. The results were that 1 ) weight loss resulted in a 51% ( P < 0.05) increase in plasma adiponectin and a 45% ( P < 0.05) increase in adipose tissue mRNA levels; 2 ) plasma adiponectin was 53% ( P < 0.01) higher in lean compared with obese men, and plasma adiponectin was inversely correlated with adiposity, insulin sensitivity, and IL-6; and 3 ) TNF-α ( P < 0.01) and IL-6 plus its soluble receptor ( P < 0.05) decreased adiponectin mRNA levels in vitro. The inverse relationship between plasma adiponectin and cytokines in vivo and the cytokine-induced reduction in adiponectin mRNA in vitro suggests that endogenous cytokines may inhibit adiponectin. This could be of importance for the association between cytokines (e.g., IL-6) and insulin resistance and atherosclerosis. interleukin-6; tumor necrosis factor-α; interleukin-8; human adipose tissue Address for reprint requests and other correspondence: J. M. Bruun, Dept. of Endocrinology and Metabolism, Aarhus Amtssygehus, Tage Hansensgade 2, DK-8000 Aarhus C, Denmark (E-mail: [email protected] ).

Brommage, Robert

doi: 10.1152/ajpendo.00470.2002pmid: 12759224

Validated methods of determining murine body composition are required for studies of obesity in mice. Dual-energy X-ray absorptiometry (DEXA) provides a noninvasive approach to assess body fat and lean tissue contents. Similar to DEXA analyses in other species, body fat measurements in mice show acceptable precision but suffer from poor accuracy. Because fat and lean tissues each contain various components, these inaccuracies likely result from selection of inappropriate calibration standards. Analysis of solvents showed that the PIXImus2 DEXA gave results consistent with theoretical calculations. Male mice weighing 26-60 g and having body fat percentages ranging from 3 to 49% were analyzed by both PIXImus2 DEXA and chemical carcass analysis. DEXA overestimated mouse fat content by an average of 3.3 g, and algorithms were generated to calculate body fat from both measured body fat values and the measured ratio of high- to low-energy X-ray attenuations. With calibration to mouse body fat content measured by carcass analysis, the PIXImus2 DEXA gives accurate body composition values in mice. PIXImus; carcass analysis; obesity; dual-energy X-ray absorptiometry Address for reprint requests and other correspondence: R. Brommage, Dept. of Endocrinology, Lexicon Genetics, 8800 Technology Forest Pl., The Woodlands, TX 77381 (E-mail: [email protected] ).