Dose-dependent effects of hypergravity on body mass in mature rats

Introduction: Previous reports have shown that exposure to hypergravity decreases rat body mass during the initial phase, with this decrease and level of gravity showing a dose-response relationship. The present study examined whether rate of body mass gain after the initial phase of exposure is attenuated by hypergravity in a dose-dependent manner and sought to identify any threshold. Methods: Male 10-wk-old rats (n = 64) were used, with 16 rats serving as 1.0-G controls, and 48 rats exposed to hypergravity for 14 d in 4 groups (1.5, 2.0, 2.5, and 3.5 G; n = 12 each). Body mass gain was evaluated according to slope of change in body mass from day 7 of exposure to hypergravity, as both absolute and relative values. Results: Slopes of body mass gain did not differ between the 1.0- and 1.5-G groups (6.09 and 5.75 g d -1 , respectively), but were significantly less for the 2.0-, 2.5-, and 3.5-G groups (4.91, 3.03 and 1.99 g d -1 , respectively) than for the 1.0- and 1.5-G groups. Body mass gain as a relative value did not differ between the 1.0-, 1.5-, and 2.0-G groups (1.5 ± 0.2, 1.6 ± 0.6 and 1.4 ± 0.3 g ·d -1 ·100g -1 body mass, respectively), but was significantly less for the 2.5-and 3.5-G groups (1.1 ± 0.6 and 0.8 ± 0.3 g·d -1 ·100g -1 body mass, respectively) than for the 1.0-, 1.5-, and 2.0-G groups. Absolute values and rate of body mass gain were reduced with increases in gravity. Conclusion: Exposure to hypergravity attenuates body mass gain in a dose-dependent manner, with a threshold possibly existing between 1.5- and 2.5-G for 10-wk-old male rats.