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Altered sympathetic nervous activity has been linked to the development and persistence of obesity, partly relating to overfeeding. Binding of the selective, positron-emitting phosphodiesterase-4 (PDE4) inhibitor (R)-[[sup.11]C]rolipram provides a direct index of the CAMP-hydrolyzing enzyme PDE4. This study examines progressive alterations in PDE4 in a high-fat-fed obese animal model. (R)-[[sup.11]C]Rolipram was injected into diet-induced obese (DIO) and diet-resistant (DR) rats; the animals were killed after 45 min, tissues were extracted, and radioactivity was quantified. Responsiveness of PDE4 to acute noradrenaline (NA) stimulation was determined by 3 h pretreatment with the NA reuptake inhibitor desipramine. There was minimal variance in caloric intake, weight gain, fasting glucose, insulin, and energy expenditure (indirect calorimetry) measures. Basal (R)-[[sup.11]C]rolipram binding was comparable between DIO and DR rats at 2 or 8 weeks of feeding. The normal increase of PDE4 levels in response to elevated NA by desipramine pretreatment was ablated in PDE4-rich tissues, including brain, heart, and skeletal muscle, of DIO animals after 8 weeks of high-fat diet. Lean DR rats maintained PDE4 responsiveness indicative of a normal NA signal transduction. Key words: diet-induced thermogenesis, sympathetic nervous system, noradrenergic signaling, (R)-[[sup.11]C]rolipram, positron emission tomography, high-fat diet, obesity. Une modification de l'activite nerveuse sympathique a ete liee au developpement et au maintien de l'obesite, decoulant en partie d'une suralimentation. La fixation de l'inhibiteur selectif de la phosphodiesterase-4 (PDE4) emetteur de positons, (R)-[[sup.11]C]rolipram, fournit un indice direct de l'enzyme PDE4 hydrolysant l'AMPc. La presente etude examine les modifications progressives de la PDE4 dans un modele animal obese soumis a une diete hyperlipidique. On a injecte le (R)-[[sup.11]C]rolipram a des rats rendus obeses par la diete (OD) et a des rats resistants a la diete (RD), sacrifie les animaux apres 45 min, extrait les tissus et quantifie la radioactivite. On a determine la reactivite de la PDE4 a une stimulation aigue induite par la noradrenaline (NA), 3 h apres un pretraitement avec l'inhibiteur de recapture de NA, desipramine. On a observe une variance minimale dans les mesures de l'apport calorique, de gain corporel, de glucose a jeun, d'insuline et de depense energetique (calorimetrie indirecte). La retention basale de (R)-[[sup.11]C]rolipram a ete comparable chez les rats OD et RD apres 2 ou 8 semaines de diete. L'augmentation normale des taux de PDE4 en reponse a l'augmentation de NA par le pretraitement a la desipramine a ete supprimee dans les tissus riches en PDE4, dont le cerveau, le coeur et le muscle squelettique, des animaux OD apres 8 semaines de diete hyperlipidique. Les rats RD maigres ont maintenu une reactivite de la PDE4 indiquant une transduction de signal normale par la NA. Mots-cles : thermogenese induite par la diete, systeme nerveux sympathique, signalisation noradrenergique, (R)-[[sup.11]C]rolipram, tomographie d'emission de positons, diete hyperlipidique, obesite. [Traduit par la Redaction], Introduction Obesity confers elevated risk for several comorbidities, including type 2 diabetes mellitus, hypertension, and cardiovascular disease (Kannel et al. 1967; Poirier et al. 2006). The sympathetic nervous system (SNS) [...]

Calorie restriction (CR) without malnutrition increases life span and delays the onset of a variety of diseases in a wide range of animal species. However, the mechanisms responsible for the retardation of aging with CR are poorly understood. We proposed that CR may act, in part, by inducing a hypometabolic state characterized by decreased reactive oxygen species (ROS) production and mitochondrial proton leak. Here, we examine the effects of long-term CR on whole animal energetics as well as muscle mitochondrial energetics, ROS production, and ROS damage. CR was initiated in male FBN[F.sub.1] rats at 6 mo of age and continued for 12 or 18 too. Mean whole body V[O.sub.2] was 34.6 (P < 0.01) and 35.6% (P < 0.001) lower in CR rats than in controls after 12 and 18 mo of CR, respectively. Body mass-adjusted V[O.sub.2] was 11.1 and 29.5% lower (both P < 0.05) in CR rats than in controls after 12 and 18 mo of CR. Muscle mitochondrial leak-dependent (State 4) respiration was decreased after 12 mo compared with controls; however, after 18 mo of CR, there were slight but not statistically significant differences. Proton leak kinetics were affected by 12 mo of CR such that leak-dependent respiration was lower in CR mitochondria only at protonmotive force values exceeding 170 inV. Mitochondrial [H.sub.2][O.sub.2] production and oxidative damage were decreased by CR at both time points and increased with age. Muscle UCP3 protein content increased with long-term CR, consistent with a role in protection from ROS but inconsistent with the observed decrease or no change in proton leak. oxidative phosphorylation; oxidative stress; metabolic control analysis; aging

Reductions in cellular oxygen consumption (V[O.sub.2]) and reactive oxygen species (ROS) production have been proposed as mechanisms underlying the anti-aging effects of calorie restriction (CR). Mitochondria are a cell's greatest 'sink' for oxygen and also its primary source of ROS. The mitochondrial proton leak pathway is responsible for 20-30% of V[O.sub.2] in resting cells. We hypothesized that CR leads to decreased proton leak with consequential decreases in V[O.sub.2], ROS production, and cellular damage. Here, we report the effects of short-term (2-wk, 2-mo) and medium-term (6-mo) CR (40%) on rat muscle mitochondrial proton leak, ROS production, and whole animal V[O.sub.2]. Whole body V[O.sub.2] decreased with CR at all time points, whereas mass-adjusted V[O.sub.2] was normal until the 6-mo time point, when it was 40% lower in CR compared with control rats. At all time points, maximal leak-dependent V[O.sub.2] was lower in CR rats compared with controls. Proton leak kinetics indicated that mechanisms of adaptation to CR were different between short- and medium-term treatments, with the former leading to decreases in protonmotive force ([DELTA]p) and state 4 V[O.sub.2] and the latter to increases in [DELTA]p and decreases in state 4 V[O.sub.2]. Results from metabolic control analyses of oxidative phosphorylation are consistent with the idea that short- and medium-term responses are distinct. Mitochondrial [H.sub.2][O.sub.2] production was lower in all three CR groups compared with controls. Overall, this study details the rapid effects of short- and medium-term CR on proton leak, ROS production, and metabolic control of oxidative phosphorylation. Results indicate that a reduction in mitochondrial V[O.sub.2] and ROS production may be a mechanism for the actions of CR. aging; oxidative stress; oxidative phosphorylation; uncoupling protein

Energy restriction (ER), without malnutrition, is the only environmental intervention that consistently increases maximum life span in laboratory rodents. One theory proposes that a reduction in energy expenditure and reactive oxygen species production is the mechanism responsible for this action of ER. To further test this theory, proton leak, [H.sub.2][O.sub.2] production, lipid peroxidation, and protein carbonyls were measured in mitochondria from FBN[F.sub.1] rats fed either a control or 40% ER diet (onset at 6 mo of age). Liver mitochondria were isolated at 7 and 12 mo of age. Liver weight decreased 25 and 36% at 1 and 6 mo of ER, respectively (P < 0.05). ER resulted in an increase (P < 0.05) in percent total polyunsaturates, n-6 polyunsaturates, and total unsaturates (6 mo only) in mitochondrial lipids. These changes, however, were not associated with significant alterations in mitochondrial function. State 4 respiration and membrane potential were not different (P > 0.05) between groups at either assessment period. Similarly, proton leak kinetics were not different between control and ER animals. Top-down metabolic control analysis and its extension, elasticity analysis, were used at the 6-mo assessment and revealed no difference in control of the oxidative phosphorylation system between control and ER rats. [H.sub.2][O.sub.2] production with either succinate or pyruvate/malate substrates was also not different (P > 0.05) between groups at either time point. In conclusion, ER did not alter proton leak or [H.sub.2][O.sub.2] production at this age or stage of restriction in liver. calorie restriction; energy expenditure; mitochondrial lipids; aging; oxidative stress