Roselis Silveira Martins da Silva

Effects of starvation on the carbohydrate and lipid metabolism in crabs previously maintained on a high protein or carbohydrate-rich diet

Abstract 1. 1. In the Chasmagnathus granulata crab fed a high protein diet, haemolymph glucose and hepatopancreas glycogen content were not greatly affected by starvation. However, muscle glycogen decreased during fasting. 2. 2. In crabs fed a carbohydrate-rich diet, hepatopancreas and muscle glycogen seem to constitute the major source of energy during starvation. 3. 3. At the end of the experimental period, the catabolism of hepatopancreas and muscle lipids suggests that in both groups the lipid metabolism was an additional source of energy during food deprivation.

Gluconeogenesis in hepatopancreas of Chasmagnathus granulata crabs maintained on high-protein or carbohydrate-rich diets☆

The capacity for glucose synthesis in Chasmagnathus granulata hepatopancreas, associated with phosphoenolpyruvate carboxykinase activity, argues in favor of this tissue as a site for gluconeogenesis. In order to obtain more information on the gluconeogenic capacity in crabs, we investigated the effects of different diets on the incorporation of 14C-alanine or 14C-lactic acid into glucose in Chasmagnathus granulata hepatopancreas, as well as on the phosphoenolpyruvate carboxykinase activity in this organ. In contrast to what occurs in vertebrates, in Chasmagnathus granulata, the intrinsic capacity of the hepatopancreas to synthetize glucose from alanine or lactic acid, and its phosphoenolpyruvate carboxykinase activity, was not influenced by high-protein or carbohydrate diets. The amount of labelled glucose recovered from 14C-alanine was significantly higher than that recovered from 14C-lactic acid, and 40 mM of alanine is not a saturated concentration for the gluconeogenic pathway. Phosphoenolpyruvate carboxykinase activity was detected into the mitochondrial (10,000 × g) and cytosol (100,000 × g) fractions. The data suggest that gluconeogenesis from 14C-alanine in the hepatopancreas from Chasmagnathus granulata fed a high-protein or carbohydrate-rich diet is equally subject to end-point inhibition by glucose, as has been found in vertebrates.

Seasonal variation in the energy metabolism in an estuarine crab, Chasmagnathus granulata (Dana, 1851)

1. 1. The effects of seasonal variation on the carbohydrate and lipid metabolism of the Chasmagnathus granulata were investigated. 2. 2. Glycemia is high in winter and summer and low in spring and fall. 3. 3. The glycogen content in the hepatopancreas and muscle is higher in fall and winter, and decreases during spring and summer. 4. 4. The muscle lipids are higher in summer, and decrease during fall and winter whereas hepatopancreas lipids are higher except in the fall. 5. 5. The crabs show change in the metabolic pattern of lipids and carbohydrates during the seasons of the year.

Effect of hyperosmotic shock on phosphoenolpyruvate carboxykinase gene expression and gluconeogenic activity in the crab muscle

Chasmagnathus granulata phosphoenolpyruvate carboxykinase (PEPCK) cDNA from jaw muscle was cloned and sequenced, showing a specific domain to bind phosphoenolpyruvate in addition to the kinase‐1 and kinase‐2 motifs to bind guanosine triphosphate (GTP) and Mg2+, respectively, specific for all PEPCKs. In the kinase‐1 motifs the GK was changed to RK. The first 19 amino acids of the putative enzyme contain hydrophobic amino acids and hydroxylated residues specific to a mitochondrial type signal. The PEPCK is expressed in hepatopancreas, muscles, nervous system, heart, and gills. Hyperosmotic stress for 24 h increased the PEPCK mRNA level, gluconeogenic and PEPCK activities in muscle.

Hepatopancreas gluconeogenesis during hyposmotic stress in crabs Chasmagnathus granulata maintained on high-protein or carbohydrate-rich diets

The incorporation of [14C]-alanine or [14C]-lactate into glucose was measured in hepatopancreas fractions from Chasmagnathus granulata crabs adapted to a high protein or a carbohydrate-rich diet and submitted or not (control group) to hyposmotic stress. Gluconeogenic capacity and phosphoenolpyruvate carboxykinase (PEPCK) activity increased during acclimation to a dilute medium in C. granulata hepatopancreas. In intact animals, high hemolymph urea levels occurred for the high-protein regimen and for crabs fed both diets and submitted to hyposmotic stress. It could be that the amino acids released during hyposmotic stress are deaminated in the hepatopancreas, and that the carbon chains are used as substrate for gluconeogenesis. Hepatopancreas gluconeogenesis seems to be one of the pathways implicated in the metabolic adjustment of the amino acid pool during hyposmotic stress in C. granulata.

Lactate metabolism in the muscle of the crab Chasmagnathus granulatus during hypoxia and post-hypoxia recovery

The present study showed that the lactate/glucose ratio in the hemolymph of Chasmagnathus granulatus maintained in normoxia (controls) was 4.9, suggesting that lactate is an important substrate for this crab. Periods of hypoxia are part of the biological cycle of this crab, and lactate is the main end product of anaerobiosis in this crab. Our hypothesis was that this lactate would be, therefore, used by gluconeogenic pathway or can be oxidized or excreted to the aquatic medium during hypoxia and post-hypoxia periods in C. granulatus. The concentrations of hemolymphatic lactate in animals in normoxia are high, and are used as an energy substrate. In hypoxia, muscle gluconeogenesis and excretion of lactate to the aquatic medium would contribute significantly in regulating the concentration of circulating lactate. Utilization of these pathways would serve the objective of maintaining the acid-base equilibrium of the organism. Muscle gluconeogenesis participates, during the recovery process, in metabolizing the lactate produced during the period of hypoxia. Lactate excretion to the external medium, was one of the strategies used to decrease the higher hemolymphatic lactate levels. However, oxidation of lactate in the muscle is not a main strategy used by this crab to metabolize lactate in the recovery periods.

Effect of hyposmotic stress on the carbohydrate metabolism of crabs maintained on high protein or carbohydrate-rich diet

Abstract 1. 1. Blood glucose of crabs Chasmagnathus granulata fed on high protein (HP) diet and exposed to 0%. salinity decreases reaching nil values at 72 hr after salinity change. However, with a carbohydraterich (HC) diet the glycemia increases after salinity change. 2. 2. Glycogen concentration of hepatopancreas and muscle in crabs fed HP diet increases at 72 hr after salinity change. Muscle glycogen did not change significantly. 3. 3. Hepatopancreas and muscle glycogen in HC group is high but decreases at 24 hr after salinity change, and remains higher than the HP group until the end of the experiment.

Effects of starvation and refeeding on energy-linked metabolic processes in the turtle (iTphrynops hilarii)

Abstract 1. 1. After 30 days without food, plasma glucose and FFA of Phrynops hilarii did not change significantly, whereas plasma insulin, estimated by a mammalian immunoassay method, decreased to about 40% of fed levels and increased 5-fold after refeecling for 72 hr 2. 2. Measurements of in vivo and in vitro rates of incorporation of [ 14 C]glucose and [ 14 C]glycine into glycogen, protein and lipid in liver, muscle and adipose tissue showed that fasting in turtles induces a marked reduction of endergonic processes which is reversed by refeecling. 3. 3. Whatever the nutritional condition, incorporation rates were always comparatively much lower in adipose tissue.

Seasonal variation of the carbohydrate and lipid metabolism in a land pulmonate gastropod, Megalobulimus oblongus

Abstract Seasonal variations of carbohydrate and lipid metabolism in Megalobulimus oblongus were investigated. Haemolymph glucose levels were higher in summer than in other seasons. The glycogen content of the hepatopancreas, muscle and mantle was constant throughout the year, except in winter when lower values were found. Hepatopancreas total lipid increased in spring, whereas gonad total lipid increased in winter and spring. Glycogen metabolism seems to constitute the source of energy substrate during winter while lipid metabolism may be related to the annual reproductive cycle.

Ketogenic diet-fed rats have increased fat mass and phosphoenolpyruvate carboxykinase activity

The ketogenic diet (KD), characterized by high fat and low carbohydrate and protein contents, has been proposed to be beneficial in children with epilepsy disorders not helped by conventional anti-epileptic drug treatment. Weight loss and inadequate growth is an important drawback of this diet and metabolic causes are not well characterized. The aim of this study was to examine body weight variation during KD feeding for 6 wk of Wistar rats; fat mass and adipocyte cytosolic phosphoenolpyruvate carboxykinase (PEPCK) activity were also observed. PEPCK activity was determined based on the [H(14)CO(3) (-)]-oxaloacetate exchange reaction. KD-fed rats gained weight at a less rapid rate than normal-fed rats, but with a significant increment in fat mass. The fat mass/body weight ratio already differed between ketogenic and control rats after the first week of treatment, and was 2.4 x higher in ketogenic rats. The visceral lipogenesis was supported by an increment in adipocyte PEPCK, aiming to provide glycerol 3-phosphate to triacylglycerol synthesis and this fat accumulation was accompanied by glucose intolerance. These data contribute to our understanding of the metabolic effects of the KD in adipose tissue and liver and suggest some potential risks of this diet, particularly visceral fat accumulation.