THE SEQUENTIAL RESTORATION OF PLASMA METABOLITE LEVELS, LIVER COMPOSITION AND LIVER STRUCTURE IN REFED CARP, CYPRINUS-CARPIO

Effect of realimentation was studied on the structure and function of liver tissue of carp, Cyprinus carpio. Yearling carp, after a 3-month starvation period, were renourished at a feeding rate of 1% body weigh t per day. Samples were taken at refeeding days 0, 1, 2, 5, 22 and 78. Analyses were made of blood metabolites, liver RNA, DNA, lipids, glyc ogen and protein and of liver enzyme activities. Additionally, liver c ytology was examined by means of qualitative and quantitative electron microscopy. The early refeeding period (up to day 5) was characterize d by a fast recovery of plasma metabolite concentrations (protein, tot al lipids, free fatty acids, glucose), a drastic augmentation of hepat ic glycogen reserves, and a pronounced increase of total liver weight and liver-somatic index. Constant values of total hepatic DNA showed t hat liver weight augmentation was not due to cell proliferation, but t o a pronounced enlargement of the existing hepatocytes. Major hunger-r elated structural modifications of carp hepatocytes such as enlarged m itochondria or prominence of the lysosomal compartment were reversed. A significant volume increase of cell nuclei, together with a particul arly strong elevation of hepatic RNA concentrations during initial rea limentation suggest an immediate stimulation of protein synthesis. Sin ce the cisternae of the endoplasmic reticulum were not reconstituted d uring that early phase, protein synthesis may have been executed mainl y by free ribosomes. With prolonged realimentation, the volume of the endoplasmic reticulum as well as total and relative contents of liver soluble protein continuously increased, whereas RNA concentrations dec reased again. An enforcement of liver oxidative capacity was indicated by the augmentation of cellular number and volume of mitochondria. Th e activities of the enzymes glucose-6-phosphate dehydrogenase and mali c enzyme, which convert excess energy into NADPH, increased steadily. Concomitantly, hepatic lipid accumulation was enhanced. In conclusion, liver metabolism during the early recovery phase seems to be dominate d both by repair processes and by intensive protein and glycogen synth esis. The liver slows down these processes during prolonged refeeding and directs an increasing percentage of energy and metabolites toward the generation of reducing equivalents and lipid reserves.