COMPARISON OF HYPERGRAVITY AND MICROGRAVITY ON RAT MUSCLE, ORGAN WEIGHTS AND SELECTED PLASMA CONSTITUENTS

Background: Centrifugation has been proposed to be one possible counte rmeasure for the skeletal muscle, organ, hormonal, and plasma chemistr y adaptations associated with chronic unloading (e.g., during spacefli ght). Hypothesis: Our hypothesis was that there would be a continuum o f physiological and morphological responses from zero gravity to hyper gravity. Methods: Adult male rats were centrifuged continuously at 2G for 14 d and the weights of limb muscles and organs, and the levels of plasma constituents were compared with the same measurements from rat s flown on a 14-d spaceflight (Cosmos 2044). Results: Mean body weight s of centrifuge rats did not change, whereas age-matched controls grew 21%. There was a sparing of muscle protein in the centrifuge rats; th e absolute weights of predominantly slow muscles in the hindlimb were maintained and the relative weights (expressed relative to body weight and as a percent difference from control) of almost all muscles studi ed were larger than control. In contrast, spaceflight resulted in a de crease in the relative weights of most extensor, but not flexor, hindl imb muscles studied. Relative organ weights, in general, were elevated in centrifuge rats compared with control rats. Relative organ weights in flight rats were similar to control, except for a decrease in test es weight. Plasma thyroxine and testosterone levels were significantly reduced following flight, whereas only thyroxine was decreased after centrifugation. Centrifugation resulted in a decrease in most other pl asma chemistry measurements, whereas flight rats showed no change or a n elevation in these measures. Discussion: These data indicate that th e physiological responses to micro-and hypergravity are often in the o pposite direction, suggesting that in general there is a continuum of physiological and morphological effects from microgravity to 1G to hyp ergravity. These data further suggest that the imposition of hypergrav ity conditions on animals that are in a microgravity environment may h ave a beneficial effect in maintaining some physiological systems at o r near control levels.