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Christian Doyon, Pierre Samson, Josée Lalonde and Denis Richard

The corticotropin-releasing factor (CRF) system is involved in numerous physiological and behavioral actions, including the regulation of energy balance. We examined the effects of the CRF1 receptor antagonist, SSR125543, on energy balance and food deprivation-induced neuronal activation in obese rats. Lean (Fa/?) and obese (fa/fa) Zucker rats were treated orally with SSR125543 at a daily dose of 30 mg/kg for 21 days. Rats were killed either fed ad libitum or food deprived for 6 h in order to induce a mild stress response in obese rats. SSR125543 reduced plasma corticosterone levels in lean rats, prevented corticosterone response to fasting in obese rats, and increased CRF mRNA levels in the paraventricular hypothalamic nucleus (PVN) of both lean and obese rats, further confirming that the antagonist partially blocked CRF1 receptors. SSR125543 increased protein gain in obese rats. Whole carcass analyses showed reduced energy and fat gains in lean rats. Consistent with reduced fat gain, circulating triglyceride and leptin levels were reduced in SSR125543-treated lean rats. In obese rats, circulating glucose levels and the homeostasis model assessment of insulin resistance index of insulin resistance were reduced by SSR125543 treatment. CRF1 receptor blockade increased uncoupling protein-1 mRNA levels in interscapular brown adipose tissue of obese rats. The antagonist partly blocked the fasting-induced changes in c-fos mRNA levels in the PVN and arcuate nucleus of obese rats. Overall, these results suggest that although SSR125543 had relatively mild effects on energy balance, CRF1 receptor blockade attenuated several metabolic effects of short-term fasting and improved plasma variables related to the metabolic syndrome and diabetes.

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Karine Blouin, Christian Richard, Gaétan Brochu, Frédéric-Simon Hould, Stéfane Lebel, Simon Marceau, Simon Biron, Van Luu-The and André Tchernof

We examined 5α-dihydrotestosterone (5α-DHT) inactivation and the expression of several steroid-converting enzymes with a focus on aldoketoreductases 1C (AKR1C), especially AKR1C2, in abdominal adipose tissue in men. AKR1C2 is mainly involved in the conversion of the potent androgen 5α-DHT to its inactive forms 5α-androstane-3α/β,17β-diol (3α/β-diol). Subcutaneous (s.c.) and omental (Om) adipose tissue biopsies were obtained from 21 morbidly obese men undergoing biliopancreatic derivation surgery and 11 lean to obese men undergoing general abdominal surgery. AKR1C2 mRNA and 5α-DHT inactivation were detected in both s.c. and Om adipose tissue. After incubation of preadipocytes with 5α-DHT, both 3α-diol and 3β-diol were produced through 3α/β-ketosteroid reductase (3α/β-HSD) activity. In preadipocyte cultures, 3α-reductase activity was significantly predominant over 3β-reductase activity in cells from both the s.c. and Om compartments. Expression levels of AKR1C1, AKR1C3 and of the androgen receptor were significantly higher in s.c. versus Om adipose tissue while mRNA levels of 17β-HSD-2 (hydroxysteroid dehydrogenase type 2) and 3(α→β)-hydroxysteroid epimerase were significantly higher in Om fat. 3α/β-HSD activity was mainly detected in the cytosolic fraction, suggesting that AKR1C may be responsible for this reaction. Experiments with isoform-specific AKR1C inhibitors in preadipocytes showed that AKR1C2 inhibition significantly decreased 3α-HSD and 3β-HSD activities (3α-HSD: 30 ± 24% of control for s.c. and 32 ± 9% of control for Om, 3β-HSD: 44 ± 12% of control for s.c.). When cells were incubated with both AKR1C2 and AKR1C3 inhibitors, no significant additional inhibition was observed. 5α-DHT inactivation was significantly higher in mature adipocytes compared with preadipocyte cultures in s.c. adipose tissue, as expressed per microgram total protein (755 ± 830 versus 245 ± 151 fmol 3α/β-diol per μg protein over 24 h, P < 0.05 n = 10 cultures). 5α-DHT inactivation measured in tissue homogenates was significantly higher in the s.c. depot compared with Om fat (117 ± 39 versus 79 ± 38 fmol 3α/β-diol per μg prot over 24 h, P < 0.0001). On the other hand, Om 3α/β-HSD activity was significantly higher in obese men (body mass index (BMI) ≥ 30 kg/m2) compared with lean and overweight men (84 ± 37 versus 52 ± 30 fmol 3α/β-diol per μg protein over 24 h, P < 0.03). No difference was found in s.c. 3α/β-HSD activity between these groups. Positive correlations were found between s.c. 5α-DHT inactivation rate and circulating levels of the androgen metabolites androsterone-glucuronide (r = 0.41, P < 0.02) and 3α-diol-glucuronide (r = 0.38, P < 0.03) and with the adrenal precursor androstenedione (r = 0.42, P < 0.02). In conclusion, androgen inactivation was detected in abdominal adipose tissue in men, with higher 3α/β-HSD activity in the s.c. versus Om depot. Higher Om 5α-DHT inactivation rates were found in obese compared with lean men. Further studies are required to elucidate whether local androgen inactivation in abdominal adipose tissue is involved in the modulation of adipocyte metabolism and regional fat distribution in men.

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Sabina Paglialunga, Patrick Schrauwen, Christian Roy, Esther Moonen-Kornips, Huiling Lu, Matthijs K C Hesselink, Yves Deshaies, Denis Richard and Katherine Cianflone

Activation of C5L2, a G-protein-coupled receptor, by acylation-stimulating protein/complement C3adesArg (ASP/C3adesArg) has been shown to stimulate triglyceride (TG) synthesis in both mature adipocytes and preadipocytes. ASP is an adipocyte-derived hormone that acts by increasing diacylglycerol acyltransferase activity and glucose transport. ASP-deficient mice (C3KO, precursor protein) are lean, display delayed postprandial TG clearance, increased food intake, and increased energy expenditure. The present study shows that C5L2KO mice on a low fat diet are hyperphagic (~60% increase in total food intake) yet maintain the same body weight and adipose tissue mass as wild-type (WT) controls. However, on a high fat diet, average adipocyte size and adipose tissue TG/DNA content were significantly reduced and postprandial TG clearance was delayed in C5L2KO. Adipose tissue TG synthesis (WT: 47.2 ± 5.6 versus C5L2KO: 7.8 ± 1.8 pmol/μg protein, P < 0.001), TG lipolysis (WT: 227.6 ± 36.4 versus C5L2KO: 45.8 ± 5.0 nmol/μg protein, P < 0.001), and fatty acid re-esterification (WT: 85.3 ± 2.4% versus C5L2KO: 59.5 ± 6.8%, P < 0.001) were significantly reduced in C5L2KO mice. Indirect calorimetry measurements revealed C5L2KO mice have unchanged oxygen consumption levels yet reduced respiratory quotient value, suggesting preferential fatty acid utilization over carbohydrate. In agreement, fatty acid oxidation was elevated in heart and skeletal muscle tissue in C5L2KO mice and skeletal muscle levels of uncoupling protein 3 (425.5 ± 86.3%, P < 0.0001), CD36 (277.6 ± 49.5%, P < 0.05), cytochrome c (252.6 ± 33.9%, P < 0.05), and phospho-acetyl CoA carboxylase (118.4 ± 9.3%, P < 0.05) were significantly increased in C5L2KO mice versus WT (100%). The study shows that in response to reduced TG storage in white adipose tissue, C5L2KO mice have developed a compensatory mechanism of increased muscle fat oxidation.

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Véronique Serre-Beinier, Christian Toso, Philippe Morel, Carmen Gonelle-Gispert, Christelle Veyrat-Durebex, Françoise Rohner-Jeanrenaud, Thierry Calandra, Thierry Roger, Richard W James, Xavier Montet, Léo Bühler, Domenico Bosco and Thierry Berney

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine produced by many cells and tissues including pancreatic β-cells, liver, skeletal muscle, and adipocytes. This study investigates the potential role of MIF in carbohydrate homeostasis in a physiological setting outside of severe inflammation, utilizing Mif knockout (MIF−/−) mice. Compared with wild-type (WT) mice, MIF−/− mice had a lower body weight, from birth until 4 months of age, but subsequently gained weight faster, resulting in a higher body weight at 12 months of age. The lower weight in young mice was related to a higher energy expenditure, and the higher weight in older mice was related to an increased food intake and a higher fat mass. Fasting blood insulin level was higher in MIF−/− mice compared with WT mice at any age. After i.p. glucose injection, the elevation of blood insulin level was higher in MIF−/− mice compared with WT mice, at 2 months of age, but was lower in 12-month-old MIF−/− mice. As a result, the glucose clearance during intraperitoneal glucose tolerance tests was higher in MIF−/− mice compared with WT mice until 4 months of age, and was lower in 12-month-old MIF−/− mice. Insulin resistance was estimated (euglycemic–hyperinsulinemic clamp tests), and the phosphorylation activity of AKT was similar in MIF−/− mice and WT mice. In conclusion, this mouse model provides evidence for the role of MIF in the control of glucose homeostasis.

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Richard Truse, Fabian Voß, Anna Herminghaus, Jan Schulz, Andreas P M Weber, Tabea Mettler-Altmann, Inge Bauer, Olaf Picker and Christian Vollmer

During circulatory shock, gastrointestinal microcirculation is impaired, especially via activation of the renin-angiotensin-aldosterone system. Therefore, inhibition of the renin-angiotensin-aldosterone system might be beneficial in maintaining splanchnic microcirculation. The aim of this study was to analyze whether locally applied losartan influences gastric mucosal perfusion (µflow, µvelo) and oxygenation (µHbO2) without systemic hemodynamic changes. In repetitive experiments six anesthetized dogs received 30 mg losartan topically on the oral and gastric mucosa during normovolemia and hemorrhage (−20% blood volume). Microcirculatory variables were measured with reflectance spectrometry, laser Doppler flowmetry and incident dark field imaging. Transpulmonary thermodilution and pulse contour analysis were used to measure systemic hemodynamic variables. Gastric barrier function was assessed via differential absorption of inert sugars. During normovolemia, losartan increased gastric µflow from 99 ± 6 aU to 147 ± 17 aU and µvelo from 17 ± 1 aU to 19 ± 1 aU. During hemorrhage, losartan did not improve µflow. µvelo decreased from 17 ± 1 aU to 14 ± 1 aU in the control group. Application of losartan did not significantly alter µvelo (16 ± 1 aU) compared to the control group and to baseline levels (17 ± 1 aU). No effects of topical losartan on macrohemodynamic variables or microcirculatory oxygenation were detected. Gastric microcirculatory perfusion is at least partly regulated by local angiotensin receptors. Topical application of losartan improves local perfusion via vasodilation without significant effects on systemic hemodynamics. During mild hemorrhage losartan had minor effects on regional perfusion, probably because of a pronounced upstream vasoconstriction.