THE EFFECTS OF INCREASED GRAVITY AND MICROGRAVITY ON CARDIAC MORPHOLOGY

Background: Our previous study of rats exposed for 14 d to microgravit y on Cosmos 2044 revealed morphological changes consistent with cardia c atrophy. Methods: In the current comparison study, light and electro n microscopic studies were performed on cardiac muscle from 10 rats ex posed to hypergravity (continuous centrifugation at 2G) for 14 d. Resu lts: Myofiber area was significantly greater in the 2G papillary muscl e as compared with muscle from 10 control rats of the same strain and size. This contrasts with the significant decrease in myofiber area pr eviously seen in the rats exposed to microgravity. At the electron mic roscopic level, general morphological features were similar in both gr oups and resembled tissue from control rats from the previous Cosmos s tudies. However, mitochondria from papillary and ventricular muscle fr om the 2G rats revealed signs of fatigue typical of the early stage of hypertrophy. These results are consistent with a state of adaptive ca rdiac hypertrophy for the 2G group.