Oxidant/Anti-Oxidant Status in Rats Exposed to Simulated Weightlessness by Hind-Limb Unloading and Reloading

ABSTRACT

Hindlimb suspension or better known as hind-limb unloading (HLU) of rats is a validated model representing weightlessness, simulating microgravity. This is accomplished by removal of weight-bearing loads from hindquarters producing a cephalic fluid shift. The current study examines whether exposure to microgravity by hind-limb unloading will activate oxidant/antioxidant defense system. Tissue levels of malondialdehyde (MDA), total glutathione (GSH+GS-SG) and superoxide dismutase (SOD) were measured in harvested tissues following HLU and reloading. To rule out any variability in normal dietary oxidant intake, all animals received in their diet Purina rat chow containing 9.6% soy meal (4.8% soy protein). Results show that tissues harvested from rats following 2 weeks of unloading had significantly elevated MDA levels ranging from 0.3 – 0.8􀀁M/mg protein when compared to paired loaded controls (0.2 – 0.4μM/mg protein, p < 0.5). Tissues from rats reloaded for 2 weeks following unloading decreased MDA levels from their peak values (p<0.05). GSH levels increased up to 350 􀀁M depending on tissues as a result of unloading, and two weeks of reloading decreased GSH levels to 250 􀀁M from their peak levels. SOD levels increased in all harvested organs in unloaded group ranging from 0.8 – 4.0􀀁M with continued increase after two weeks of reloading, p < 0.05). Our data indicate that oxidative stress is induced during unloading as evidenced by increased tissue MDA levels. The response involves an increase in GSH and SOD levels, but two weeks of reloading decreased MDA and GSH levels, while further increasing SOD levels, implying the tissue adaptation to induced oxidative stress.