PROTEIN AND LIPID UTILIZATION DURING FASTING WITH SHALLOW AND DEEP HYPOTHERMIA IN THE EUROPEAN HEDGEHOG (ERINACEUS-EUROPAEUS)

We investigated whether the relative contributions of body protein and lipid reserves differ according to the level of energy expenditure in fasting animals. Protein and lipid utilization was therefore quantified and compared in hedgehogs which fasted with shallow and deep hypothermia, i.e. by exposure at 5 or 20 degrees C ambient temperature. Body composition was determined for every 150-g decrease in mass throughout the experiment, allowing the calculation of regression lines between body mass (independent variable, x) and body composition (dependent variable, y: water, protein, neutral lipids, phospholipids and cholesterol). There were highly significant (P<0.001) linear decreases in all body components with decreasing body mass in both groups of hedgehogs. Neutral lipids were the main component of the total body mass loss (54%) in fasted animals with shallow and deep hypothermia, percentages of water (26-30%) and protein (10-11%) being lower, and those of phospholipid and cholesterol negligible (<0.5%). In spite of different levels in energy expenditure (2.54 and 1.07 W . kg(-1) in shallow- and deep-hypothermal fasting hedgehogs, respectively), the energy sources were identical in both groups, neutral lipid being the main fuel (91-92%) and body protein accounting for the remainder (8-9%). Prolonged fasting with shallow and deep hypothermia were marked by low alaninemia and glycemia, while plasma free fatty acids and beta-hydroxybutyrate were elevated. These data therefore indicate that the relative contribution of lipid and protein is similar during prolonged fasting with shallow and deep hypothermia, i.e. there is no specific effect of deep hypothermia on body fuel utilization. The tolerance of a much longer fast in deep-hypothermal hedgehogs can simply be attributed to the lower rates of lipid and protein utilization as a result of the lower level of energy expenditure.