RELATIONSHIP BETWEEN SKELETAL-MUSCLE LIPOPROTEIN-LIPASE ACTIVITY AND 24-HOUR MACRONUTRIENT OXIDATION

A low ratio of whole-body 24-h fat/carbohydrate (CHO) oxidation has be en shown to be a predictor of subsequent body weight gain. We tested t he hypothesis that the variability of this ratio may be related to dif ferences in skeletal muscle metabolism. Since lipoprotein lipase (LPL) plays a pivotal role in partitioning lipoprotein-borne triglycerides to adipose (storage) and skeletal muscle (mostly (oxidation), we postu lated that a low ratio of fat/CHO oxidation was associated with a low skeletal muscle LPL (SMLPL) activity. As an index of substrate oxidati on, 24-h RQ was measured under sedentary and eucaloric conditions in 1 6 healthy nondiabetic Pima males. During a 6-h euglycemic, hyperinsuli nemic clamp, muscle biopsies were obtained at baseline, 3, and 6 h. He parin-elutable SMLPL activity was 2.92 +/- 0.56 nmol free fatty acids/ g . min (mean +/- SD) at baseline, was unchanged (2.91 +/- 0.51) at th e third hour, and increased significantly (P < 0.05) to 3.13 +/- 0.57 at the sixth hour of the clamp. The mean (of baseline and 3-h) SMLPL a ctivity correlated inversely with 24-h RQ (r = 0.57, P < 0.03) but not with body size, body composition, or insulin-mediated glucose uptake. Since SMLPL activity is related to the ratio of whole body fat/CHO ox idation rate, a decreased muscle LPL activity may, therefore, predispo se to obesity.