Hepatopancreas gluconeogenesis and glycogen content during fasting in crabs previously maintained on a high-protein or carbohydrate-rich diet.

The present study assessed the effect of different fasting times on the in vitro gluconeogenic capacity of Chasmagnathus granulata crabs previously adapted to a high-protein (HP) or carbohydrate-rich (HC) diet using the incorporation of [U-(14)C]l-lactate or [U-(14)C]l-alanine into glucose. We also recorded haemolymphatic glucose and hepatopancreatic glycogen levels. In the HP group, on the third day of fasting there were decreases in the synthesis of glucose from (14)C-alanine and in haemolymph glucose. After 15 days of fasting, haemolymph glucose and hepatopancreatic glycogen levels were maintained by an increase in the conversion of (14)C-alanine into glucose. However, after 21 days of fasting the gluconeogenic capacity was decreased and hepatopancreas glycogen concentration was reduced. In the HC group, hepatopancreatic glycogen was the energy source during the first 6 days of fasting. Gluconeogenesis from (14)C-lactate decreased after 6 days of fasting, remaining low until 21 days of fasting. The conversion of (14)C-alanine into glucose was increased after 15 days fasting and hepatopancreatic glycogen was raised in relation to that present after a 6-day fasting. In both dietary groups the stabilization in the levels of haemolymph glucose after 21 days fasting may result from a reduction in metabolic rate during restricted feeding.

Hepatopancreas gluconeogenesis during anoxia and post-anoxia recovery in Chasmagnathus granulata crabs maintained on high-protein or carbohydrate-rich diets.

C. granulata is a semiterrestrial crab that lives in the mesolittoral and the supralittoral zones of estuaries and faces hypoxia and anoxia when exposed to atmospheric air. The carbohydrate or protein content of the diets administered to the crabs induced different metabolic adjustments during anoxia and post-anoxia recovery period. During the first hour in anoxia a marked increase in L-lactate concentration in hemolymph was induced, followed by a reduction in its levels accompanied by two peaks in hepatopancreas gluconeogenic capacity. Anoxia exposure did not induce a reduction in the hepatopancreas phosphoenolpyruvate carboxykinase activity in either dietary group. Our results suggest that in anaerobiosis this crab uses the conversion of lactate to glucose in hepatopancreas to maintain the acid-base balance and the glucose supply. In post-anoxia recovery, the fate of L-lactate is the hepatopancreas gluconeogenesis in high protein maintained crabs. On the other hand, in the crabs maintained on carbohydrate-rich diet the L-lactate levels decreased gradually in the hemolymph during the post-anoxia recovery; however, the hepatopancreas gluconeogenesis did not increase. In both dietary groups, an increase in the gluconeogenic capacity of hepatopancreas occurred at 30 h of post-anoxia recovery.

Effects of starvation on haemolymphatic glucose levels, glycogen contents and nucleotidase activities in different tissues of Helix aspersa (Müller, 1774) (Mollusca, Gastropoda).

In the present study, the glucose concentration in the haemolymph and glycogen levels were determined in the various body parts of the Helix aspersa snail after feeding lettuce ad libitum and after various periods of starvation. To characterize the effect of starvation on nucleotidase activity, enzyme assays were performed on membranes of the nervous ganglia and digestive gland. Results demonstrated the maintenance of the haemolymph glucose concentration for up to 30 days of starvation, probably due to the consumption of glycogen from the mantle. In the nervous ganglia, depletion of glycogen occurs progressively during the different periods of starvation. No significant changes were observed on ATP and ADP hydrolysis in the membranes of nervous ganglia and no alterations in Ca2+ -ATPase and Mg2+ -ATPase occurred in the membranes of the digestive gland of H. aspersa during the different periods of starvation. Although there were no changes in the enzyme activities during starvation, they could be modulated by effectors in situ with concomitant changes in products/reactants during starvation.