Restricted feeding schedules entrain behavioral and physiological circadian rhythms, which depend on a food-entrainable oscillator (FEO). The mechanism of the FEO might depend on digestive and endocrine processes regulating energy balance. The present study characterizes the dynamics of circulating corticosterone, insulin, and glucagon and regulatory parameters of liver metabolism in rats under restricted feeding schedules. With respect to ad libitum controls, food-restricted rats showed 1) an increase in corticosterone and glucagon and a decrease in insulin before food access, indicating a predominant catabolic state; and 2) a reduction in lactate-to-pyruvate and beta-hydroxybutyrate-to-acetoacetate ratios, indicating an oxidized cytoplasmic and mitochondrial redox state in the liver metabolism. All these changes were reversed after feeding. Moreover, liver energy charge in food-restricted rats did not show a significant modification before feeding, despite an increase in adenine nucleotides, but showed an important decrease after food intake. Variations detected in the liver of food-restricted rats are different from those prevailing under 24-h fasting. These observations suggest "anticipatory activity" of the liver metabolism to optimize the processing of nutrients to daily feeding. Data also suggest a possible relationship of the liver and endocrine signals with the FEO.

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SUMMARY:The oxygen free radicals-induced lipid peroxidation (LP) has been implicated in the pathogenesis of acute ethanol-induced gastric mucosal lesions. However, the role of LP in the generation of chronic gastric mucosal injury is unknown. We have developed a model of chronic mucosal injury induced by continuous ethanol ingestion for 5 days and characterized by marked alterations in plasma membranes from gastric mucosa. Therefore, LP was evaluated in this experimental model. Indicators of peroxidative activity, mucosal glutathione content, thymidine kinase activity (an index of cell proliferation), and histamine H 2 -receptor (H 2 R) binding constants were quantified in animals undergoing gastric mucosal damage. The effect of famotidine, a H 2 R antagonist that readily ameliorates the chronic mucosal injury, was also tested. Increased free radicals and LP levels were detected during gastritis; however, a second, higher peak of LP was noted in mucosal plasma membranes after ethanol withdrawal (recovery period). This further increase of LP coincided with active cell proliferation, decreased mucosal glutathione levels, and diminished specific cimetidine binding by H 2 R. Administration of famotidine accelerated the mucosal proliferative process, inducing the second lipoperoxidative episode sooner, and preserved the content of glutathione. In addition, LP correlated directly with cell proliferation and inversely with mucosal membrane cimetidine binding. In conclusion, LP seems to be involved in chronic ethanol-induced gastric mucosal injury. However, a further enhancement of plasma membrane LP occurred, associated with increased DNA synthesis and diminished cimetidine binding by membrane H 2 R. Therefore, increased LP could also participate in the compensatory mucosal proliferation initiated after ethanol withdrawal. (Lab Invest 2000, 80:1161-1169.

IntroductionIntracellular Ca 2+ dynamics is a key factor in cellular signaling and physiology (for a review, see Bootman et al., 2001). In particular, the system of endomembranes that forms the sarco(endo)plasmic reticulum plays a vital role in Ca 2+ handling in most eukaryots (Carafoli and Klee, 1999). In this compartment two families of intracellular Ca 2+ release channels have been characterized: the ryanodine receptors (RyR) and the inositol 1,4,5-trisphosphate receptors (IP3R) (Nori et al., 1993). Besides these, there is evidence for two more intracellular Ca 2+ releasing channels: the NAAPD and the sphingolipid receptors (Petersen and Cancela, 1999;Cancela, 2001). Ca 2+ re-uptake by the sarco(endo)plasmic reticulum is mediated by the thapsigargin-sensitive sarco(endo)plasmic reticulum Ca 2+ ATPase (SERCA), whose structure and function has been studied extensively in mammalian muscle systems (MacLennan, 1990).The development of the fruit fly Drosophila melanogaster is amenable to multidisciplinary analyses (for a review, see Campos-Ortega and Hartenstein, 1997) and is thus a powerful system in which to examine the role of these proteins in intracellular Ca 2+ homeostasis. In this organism, a single RyR gene with 26 exons, dry, and a single IP3R gene with 12 exons, dip, exist and have been genetically characterized (Takeshima et al., 1994;Sinha and Hasan, 1999). In contrast, RyR and IP3R in vertebrates are coded by at least three different genes that, due to alternative splicing, present a large number of isoforms (Rubtsov and Batrukova, 1997;Marks, 1997). A similar situation occurs with the thapsigargin-sensitive Ca 2+ ATPase. In D. melanogaster only one gene coding for this P-type ATPase has been detected, CaP60A (Magyar et al., 1995); whereas in vertebrates, at least three different isoforms of this Ca 2+ ATPase have been reported (Misquitta et al., 1999).Despite extensive genetic and molecular biology data for these proteins, there is a dearth of basic biochemical information on the Drosophila RyR, IP3R and SERCA proteins. In order to reap the benefit from a genetic and molecular biology tractable model organism with single RyR, IP 3 R and SERCA proteins, we characterize here these important molecules using Drosophila native endomembranes.

Food anticipatory activity (FAA) is an output of the food-entrained oscillator (FEO), a conspicuous biological clock that expresses when experimental animals are under a restricted food schedule (RFS). We have shown that the liver is entrained by RFS and exhibits an anticipatory response before meal time in its oxidative and energetic state. The present study was designed to determine the mitochondrial oxidative and phosphorylating capacity in the liver of rats under RFS to further support the biochemical anticipatory role that this organ plays during the food entrainment (9). Metabolic and functional parameters of liver mitochondria were characterized before (0800 h), during (1100 h), and after (1400 h) FAA. The main results were as follows. First, there was an enhancement during FAA (1100 h) in 1) oxidative capacity (site I of the electron transport chain), 2) phosphorylating ability (estimated by ATP synthesis), and 3) activities of NADH shuttles. Second, after rats were fed (1400 h), the phosphorylating capacity remained high, but this was not the case for the respiratory control ratio for site I. Finally, in the three experimental conditions before, during, and after FAA, an increment was detected in the H(+) electrochemical potential, due to an elevation in mitochondrial membrane potential, and in mitochondrial yield. Most of the changes in mitochondrial properties related to RFS were also present when results were compared with those from the 24-h fasted group. In conclusion, the results support the notion that a distinctive rheostatic state is installed in the metabolic activity of the liver when FEO is being expressed.