Modulation of bone mass and turnover in growing rats by voluntary weight-bearing exercise and glucose supplementation.

Female Sprague-Dawley rats, 9 weeks of age, were assigned to four groups: Group 0 (n = 8) was dissected for base-line control, and the other three groups were fed for 3 mo: Group 1 (n = 9), sedentary controls; Group 2 (n = 6), running rats housed in a cage with a treadmill and pair-fed with Group 1; and Group 3 (n = 7), running rats, pair-fed and allowed free access to additional glucose. The distances of voluntary running did not significantly differ between Groups 2 and 3. Menstrual cycles in these rats were apparently maintained as observed from daily running distances. The amount of glucose taken by rats in Group 3 was 3.5 +/- 0.4 (mean and SE) g/d. Body weight (BW) at the end of the experiment for Groups 1, 2, and 3 were 295.0 +/- 7.9, 211.7 +/- 5.4 (p < 0.001 vs. Group 1), and 259.0 +/- 3.5 g (p < 0.01 vs. Group 2), respectively. The parameters of bone mass such as ash weights of the femur and bone mineral content of the lumbar spine and the tibia in Groups 1 and 2 did not differ, but the values were significantly greater in Group 3 than in Group 2. However, these parameter values corrected for BW were significantly greater in Group 2 than in Group 1 and did not significantly differ between Groups 2 and 3. The parameters of bone formation, such as serum bone alkaline phosphatase activity levels and trabecular bone formation rates corrected for BW, were significantly greater in Group 2 than in Group 1 but did not differ between Group 2 and 3. However, the parameters of bone resorption, such as serum tartrate resistant acid-phosphatase levels, were significantly less in Group 3 than in Group 2. These results suggest that voluntary running augments the age-dependent increase in bone mass by modulating the bone turnover when an adequate energy source is supplied under conditions of normal menstruation, and an adequate supply of energy could be necessary to enhance the age-dependent increase in bone mass.