Glycogen repletion following burst activity: A carbohydrate-sparing mechanism in animals adapted to arid environments?

The Western chestnut mouse (Pseudomys nanus ferculinus) is one of several n ative rodent species adapted to the arid environments of Australia. Since t hese environments are often associated with a paucity in dietary carbohydra te, the problem arises as to the mechanism whereby these rodents replete th eir stores of muscle glycogen when recovering from high intensity physical activity. This is an important issue since the maintenance of adequate stor es of muscle glycogen is crucial to support the energy demands associated w ith 'flight or fight' responses. Whilst it is known that food ingestion pos t-exercise is required for the total repletion of muscle glycogen in rats a nd humans, our findings indicate that the Western chestnut mouse has the im pressive capacity to replete completely its stores of muscle glycogen, even in the absence of food intake. Indeed during recovery from burst activity which results in the massive breakdown of the stores of muscle glycogen, th e levels of glycogen return back to pre-exercise levels within only 50 minu tes despite the absence of food intake. This capacity is important in the b roader context of nutritional adaptation to arid/seasonally-arid regions si nce it allows muscles to replete their fuel stores even when food is not av ailable. How common is this strategy among desert-adapted mammal species is a question yet to be answered. (C) 1999 Wiley-Liss, Inc.