Influence of Fasting and Diet on Lipogenic Enzymes in the American Eel, Anguilla rostrata LeSueur

Abstract

To determine the potential site(s) of fatty acid synthesis and source(s) of reducing equivalents, the activities of the cytoplasmic NADPH producing enzymes--isocitrate dehydrogenase (IDH), malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH), and of aconitase, ATP-citrate lyase (CCE) and malate dehydrogenase (MDH) were measured in homogenates of liver, intestine, visceral fat, red muscle and white muscle of eels (Anguilla rostrata) fed beef liver or worms, or fasted for 2 to 6 months. There were no differences in enzyme activities between eels fed beef liver or fasted for 2 months. Eels fed worms had significantly greater G6PDH activity than fasted eels. Liver size and hepatosomatic index decreased in fasted eels, but lipid content per gram of liver or muscle increased. Based on the total activities of the NADPH producing enzymes, the liver appeared to be the primary organ for lipogenesis, although the intestine contained active lipogenic enzymes as well. In the liver, IDH had the lowest Km (NADP) and highest activity of the NADP-dehydrogenases. In the liver cytoplasm, the low activities of CCE and ME and the presence of an active aconitase, with a 20-fold greater affinity than CCE for citrate, suggest tha citrate cleavage is unimportant and that IDH is a major source of reducing equivalents. The source of carbon for fatty acid synthesis is discussed in relation to these conclusions.

Relation between dietary lipid level and voluntary feed intake, growth, nutrient gain, lipid deposition and hepatic lipogenesis in rainbow trout

“…As reported by Lin et al [68] who compared lipid biosynthesis by the liver and visceral adipose tissue from coho salmon, Oncorhynchus kisutch, and confirmed by further studies in other fish species [7,43,67], the liver accounts for more de novo lipid synthesis than the adipose tissue. Body lipids can also be synthesised de novo from other carbon donors, such as carbohydrates or amino acids, as shown by the fat gain / fat intake ratio above 100% [18,60].…”

“…In man [48] and most avian species [45,48], the liver is identified as the major contributor to fatty acid synthesis. In fish, most studies [7,43,67,68] have demonstrated the primary role of the liver in de novo fatty acid synthesis, adipose tissue being better adapted for storage of dietary lipids or neo-synthesised fatty acids from the liver [23,43].…”

Effects of long-term starvation on hepatocyte ultrastructure of olive flounder Paralichthys olivaceus

“…Differences among species are observed mainly in the amount of lipid, which may increase or decrease (Langer and Storch, 1978;Aster and Moon, 1981). Increased lipid deposits could be indicative of lipoid liver disease (ceroidosis), which can develop in fish fed a diet in which the lipid component has become rancid and the vitamin components are insufficient, e.g., "trash fish" or pelleted rations (Smith, 1979), or a diet with high carbohydrate and low protein content (Hille et al, 1980).…”

Insulin Stimulates Lipogenesis and Attenuates Beta‐Oxidation in White Adipose Tissue of Fed Rainbow Trout

“…When compared with other fish species the reducing power generated in trout WAT (5.3 nmol NADPH min -1 g -1 = 347 nmol NADPH min -1 mg protein -1 ) lipogenesis is variable and related to the species and the assay temperature. Trout WAT generates up to 4.5-fold more NADPH than the eel (assessed at 20°C) [15] and catfish (assessed at 25°C) [16] visceral adipose tissue. When compared with the salmon (assessed at 18°C) [17], the difference is tenfold higher.…”