Voluntary Wheel Running Decreases Adipose Tissue Mass and Expression of Leptin mRNA in Osborne-Mendel Rats

Abstract

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.

Poor Wheel-Running Exercise Can Decrease Blood Pressure through Hormonal Control and Increase Endurance Exercise Capacity in Middle-Aged Normal Rats

“…Moreover, MFM of our WR rats, which is correlated positively with BW or waist circumference regarded as one of risk factors for metabolic syndrome, was found to decrease as daily running distance increased, suggesting that voluntary WR exercise mainly utilized energy released from the augmented lipid metabolism. In addition, adipocyte size distribution in the present WR rats shifted leftward compared with that of the sedentary rats, as seen in WR exercised OLETF [17] and Osborne-Mendel rats [20]. In agreement with several previous studies of voluntary WR exercise [16] [17] [20]- [23], circulating levels of adipocyte-secreted leptin were significantly lower in our WR than in the sedentary rats, resulting from the decreased MFM of the WR rats.…”

“…In addition, adipocyte size distribution in the present WR rats shifted leftward compared with that of the sedentary rats, as seen in WR exercised OLETF [17] and Osborne-Mendel rats [20]. In agreement with several previous studies of voluntary WR exercise [16] [17] [20]- [23], circulating levels of adipocyte-secreted leptin were significantly lower in our WR than in the sedentary rats, resulting from the decreased MFM of the WR rats. In fact, the reduction in leptin secretion and its mRNA expression was reported to be closely associated with smaller adipocyte size [25] [26].…”

“…In the previous studies, 4-or 7-week WR exercise that started at 3 -5 weeks of age caused a decrease in various fat pad mass [20] [23]. In this study, likewise, MFM weighed less in the WR exercised than in the sedentary animals.…”

“…In the previous studies using 4--6-week-old genetic model rats [12] [14] [15] [17] or high-fat diet-induced obesity rats [20] [23], on the other hand, these juvenile rats showed an extremely high WR activity (3-12 km of daily running distance). To compensate the increased energy expenditure by the WR exercise, they also showed a significantly higher caloric intake compared with the control sedentary rats [17] [23].…”

“…Epidemiological studies showed that physical activity of moderate intensity, like walking and jogging, could reduce the risk of developing type 2 diabetes and coronary heart disease [10] [11]. Every possible mechanism for this risk reduction has been explored, using cages equipped with a running wheel, in several rodent studies, where various genetic models including gene-modified animals [12]- [19] and high-fat diet-sensitive obesity models [20]- [23] start on voluntary wheel running (WR) during juvenile or young period, but not during adult period. Thus, the preventive effects of WR exercise on development of metabolic syndrome have not been fully studied in adult rats as yet.…”