Radioglucose metabolism by Richardson's ground squirrels in the weight-gain and weight-loss phases of the circannual cycle.

Captive fed, starved, and refed Richardson's ground squirrels in the weight-gain and weight-loss phases of the circannual cycle were injected with radioglucose and the activity of the label in skeletal muscle proteins and white adipose tissue lipids four hours after injection was used to determine if lean body mass and white adipose tissue would be rapidly restored when starved animals were refed. Starvation for six days reduced carcass mass 27-31% and white adipose tissue mass 23-24% (Table 1). Activity of the label in both tissues of weight-gain and weight-loss animals was reduced by starvation. After four days of refeeding activities returned to levels similar to those in fed animals, with the exception of lower activity in skeletal muscle proteins of weight-gain animals. Furthermore, activity in each tissue fraction of starved and refed weight-gain animals was similar to that in weight-loss animals when expressed as per cent of activity in the respective fed state (Table 2). Radioglucose incorporation indicated that when skeletal muscle and adipose tissue are depleted by starvation, distribution of the label upon refeeding is similar to that in the fed state. Four days after refeeding weight-gain phase ground squirrels had restored 5.5 g of lean body mass and 7.5 g of adipose tissue, including 1.4 g (6 kcal) of protein and 7.0 g (66 kcal) of lipid, respectively. These results are also consistent with the fed state, in which weight-gain animals were depositing more lipid than lean body mass.