Effect of short-term microgravity and long-term hindlimb unloading on rat cardiac mass and function

The purpose of this study was to test the hypothesis that exposure to short -term microgravity or long-term hindlimb unloading induces cardiac atrophy in male Sprague-Dawley rats. For the microgravity study, rats were subdivid ed into four groups: preflight (PF, n = 12); flight (Fl, n = 7); flight cag e simulation (Sim, n = 6), and vivarium control (Viv, n = 7). Animals in th e Fl group were exposed to 7 days of microgravity during the Spacelab 3 mis sion. Animals in the hindlimb-unloading study were subdivided into three gr oups: control (Con, n = 20), 7-day hindlimb-unloaded (7HU, n = 10), and 28- day hindlimb-unloaded (28HU, n = 19). Heart mass was unchanged in adult ani mals exposed to 7 days of actual microgravity (PF 1.33 +/- 0.03 g; Fl 1.32 +/- 0.02 g; Sim 1.28 +/- 0.04 g; Viv 1.35 +/- 0.04 g). Similarly, heart mas s was unaltered with hindlimb unloading (Con 1.40 +/- 0.04 g; 7HU 1.35 +/- 0.06 g; 28HU 1.42 +/- 0.03 g). Hindlimb unloading also had no effect on the peak rate of rise in left ventricular pressure, an estimate of myocardial contractility (Con 8,055 +/- 385 mmHg/s; 28HU 8,545 +/- 755 mmHg/s). These data suggest that cardiac atrophy does not occur after short-term exposure to microgravity and that neither short- nor long-term simulated microgravit y alters cardiac mass or function.