Lipid-based Metabolism Research Articles

Respiratory, metabolic, and acid-base correlates of aerobic metabolic rate reduction in overwintering frogs.

Aerobic metabolic rates (MO2) and respiratory quotients (RQ = CO2 production/MO2) were measured contemporaneously in hibernating frogs Rana temporaria (L.), submerged for 90 days at 3 degrees C. After 3 mo of submergence in fully aerated water, MO2 levels were 61% of those seen at the same temperature before hibernation. Over the first 40 days of hibernation, RQ values (< or = 0.82) favored a lipid-based metabolism that progressively shifted to an exclusively carbohydrate metabolism (RQ = 1.01) by 90 days of hibernation. Liver glycogen concentrations fell by 68% during the first 8 wk of submergence, thereafter exhibiting a less rapid rate of utilization. Conversely, muscle glycogen concentrations remained stable over the first 2 mo of the experiment before falling by 33% over the course of the remaining 2 mo, indicating that the frog was recruiting muscle glycogen reserves to fuel metabolism. Submerged frogs exhibited an extracellular acidosis during the first week of submergence, but over the course of the next 15 wk "extracellular pH" values were not significantly different from the values obtained from the control air-breathing animals. The initial extracellular acidosis was not mirrored in the intracellular compartment, and the acid-base state was not significantly different from the control values for the first 8 wk. However, over the subsequent 8- to 16-wk period, the acid-base status shifted to a lower intracellular pH-HCO3 concentration set point, indicative of a metabolic acidosis. Even so, there was no indication that the acidosis could be attributed to anaerobic metabolism, as both plasma and muscle lactate levels remained low and stable. Muscle adenylate energy charge and lactate-to-pyruvate and creatine-to-phosphocreatine ratios also remained unchanged throughout hibernation. The capacity for profound metabolic rate suppression together with the ability to match substrate use to shifts in aerobic metabolic demands and the ability to fix new acid-base homeostatic set points are highly adaptive, both in terms of survival and reproductive success, to an animal that is often forced to overwinter under the cover of ice.

A comparative study on the nutritional quality of decapsulated Artemia cysts, micro-encapsulated eng diets and enriched dry feeds for Clarias gariepinus (Burchell) larvae

The nutritional value of several dry test diets for larvae of the African catfish, Clarias gariepinus, was determined. Dried and decapsulated cysts of Artemia gave consistently the best growth and survival rate (over 100 mg and 96%, respectively, after 2 weeks). Dry larval feeds enriched with an acetone extract of Artemia resulted in low growth and extremely low survival rates (less than 20%). The hepatocyte ultrastructure indicated a nutritional deficiency in this diet. Microencapsulated egg diets resulted in high survival rates (varying between 64 and 93%) but low and varying growth rates. The best growth was attained after addition of casein and a vitamin/mineral mix to the egg diet. The hepatocyte ultrastructure revealed a shift from a glycogen to a lipid-based metabolism, which is related to the high fat content of the egg diets. According to the hepatocyte structure, the egg diets provide all essential nutrients. It is therefore hypothesized that the low growth is caused by a decreased feed intake which again may be related to the high fat content of the diets.