The effect of glucocorticoid treatment on denervated rat hemidiaphragm.

The degenerative process in phrenic nerve motor nerve terminals following nerve section was analyzed in rats that had previously been subjected to an intensive short term regimen of the steroid preparation triamcinolone. Morphological studies indicated that the onset time of degeneration was similar to that of untreated rats but less severe, and the time for maximal degenerative changes was increased. Concurrent to the preservation of motor nerve terminal structure under conditions of denervation, triamcinolone also induced myopathies in the diaphragm, the white muscle fibers being predominantly affected. Due to the structural aberrations of muscle, the indirect and direct twitch response of hemidiaphragms in triamcinolone treated rats was depressed. Data obtained from indirect post-tetanic potentiation (PTP) responses, however, did express the anatomical preservation of motor nerve terminals. These findings may add support to previous observations for the basis of effectiveness of the glucocorticoids in the treatment of neuromuscular disorders.