ENERGY-EXPENDITURE IN RHESUS-MONKEYS (MACACA-MULATTA) DURING SPACEFLIGHT USING DOUBLY LABELED WATER ((H2O)-H-2-O-18)

The mean daily energy expenditure rates of three rhesus monkeys (Macac a mulatta) were determined during spaceflight on the joint US-Russian Cosmos 2044 and 2229 missions by the doubly labeled water ((H2O)-H-2-O -18) method. In-flight values were compared with ground data obtained from seven measurements taken from six chair-adapted control monkeys. The mean energy expenditure for the ground control determinations was 94.5 +/- 6.4 kcal . kg(-1). day(-1) (n = 6). The mean in-flight energy expenditure, 55.1 +/- 8.0 kcal . kg(-1)day(-1) (n = 3), was significa ntly less than the mean ground control value (P < 0.05). These data su ggest that energy expenditure in restrained rhesus monkeys is signific antly reduced during spaceflight.