The purpose of this study was to assess the effects of voluntary wheel running on the expression of
leptin mRNA in rats that are either sensitive (OM) or resistant (S5B/Pl) to diet-induced
obesity. Male OM and S5B/Pl rats had ad libitum access to standard rodent diet and water. At 3-5 weeks of age, animals of both strains were randomly assigned to either an exercise or sedentary control group. The exercise groups had 24-h access to a running wheel, and they trained for 7 weeks. During weeks 1-4, animals in both OM and S5B/Pl exercise groups progressively increased their running. During weeks 5-7, S5B/Pl exercisers tended to run more than did OM (approximately 60 vs. 45 km/week), but by the end of the study both groups had an equally greater heart weight (mg/g
body weight) and planteris
citrate synthase activity than their sedentary controls. Oral
glucose tolerance tests performed during the last week of training revealed that compared with their appropriate controls,
insulin sensitivity was enhanced (P < 0.05) in OM but not in the S5B/Pl wheel-running groups. Inguinal, epididymal, and retroperitoneal fat pads weighed less in the running than in the nonrunning groups of both strains (P < 0.01). Additionally, exercised animals had an increased percentage of smaller cells (40-60 microm; P < 0.05) and a decreased percentage of larger cells (120-160 microm; P < 0.05) in the epididymal fat depot. Epididymal
leptin mRNA measured by Northern blot analysis was reduced in the exercise-trained rats of both strains (P < 0.05). Furthermore, serum
leptin was reduced in exercise-trained compared with the control animals of both strains. In comparison to S5B/Pl, control OM animals exhibited both a higher expression and higher circulating levels of
leptin (P < 0.05). While serum
leptin levels were decreased and food intake was increased in the exercise-trained animals of both strains (P < 0.05), the exact relationship between exercise,
leptin, and food intake in this rat model of dietary
obesity remains to be determined. Nonetheless, these results suggest that the expression and secretion of
leptin can be influenced by exercise training and that these changes (i.e., reduced expression and secretion of
protein) can occur independently of changes in whole-body
insulin sensitivity and susceptibility to diet-induced
obesity.