Influence of acute thermal stress and maternal diet on metabolic rate of obese (ob/ob) and lean mice at two weeks of age.

The metabolic response of one- and two-week-old obese (ob/ob) and lean mice to acute thermal stress, and the influence of maternal diet on body fat and metabolic rates of these mice, were evaluated. Both obese and lean pups increased their rate of oxygen consumption 62 to 67% when exposed to 25 degrees C for 20 minutes rather than to 35 degrees C. Obese pups exposed to an intermediate temperature (30 degrees C), however, increased their rate of oxygen consumption less (35%) than did lean mice (55%) exposed to the same temperature. Reports in the literature suggest that adult obese mice have a markedly reduced ability to increase their oxygen consumption when cold-stressed, but the present results indicate that young obese mice may have less impairment in their capacity to increase oxygen consumption. Two-week-old obese pups contained more fat and consumed less oxygen than lean littermates. The maternal diet was manipulated to increase the body fat content of two-week-old pups to equal that of obese mice, but obese pups still consumed less oxygen than did the lean pups. We, thus, conclude that factors other than differences in body fat content are responsible for the lowered oxygen consumption observed in young obese mice.