A model for hypokinesia: effects on muscle atrophy in the rat

Abstract

Hypokinesia in the hindlimbs of rats was induced by suspension; a newly developed harness system was used. The animal was able to use its forelimbs to maneuver, within a 140.degree. arc, to obtain food and H2O and to permit limited grooming of the forequarters. The hindlimbs were nonload bearing for 7 days; following a 7 day period of hypodynamia, selected animals were placed in metabolic cages for 7 days to study recovery from hypokinesia. During the 7-day period of hypokinesia, there was evidence of muscle atrophy. Gastrocnemius weight decreased, renal papillary urea content increased and daily urinary losses of urea, NH3 and 3-methylhistidine increased. During the 7-day recovery period muscle mass and excretion rate of urea, NH3 and 3-methylhistidine returned to control levels. Ca balance was positive throughout the 7-day period of hypokinesia. Hypertrophy of the adrenals suggested the occurrence of some level of stress, despite the apparent behavioral adjustment to the suspension harness. Significant muscle atrophy and parallel changes in N metabolism evidently occur in suspended rats, and these changes are readily reversible.