Extensor muscle responses to triamcinolone

Abstract

Triamcinolone acetonide (20 mg/kg) was administered intraperitoneally on each of 4 days to female rats and several mechanical and electrical properties of extensor muscle were analyzed. After 1 day of treatment, the duration of the twitch was increased but neither the twitch nor the tetanic tension was affected by the drug. After 4 days of treatment both twitch and tetanic tensions showed a slight increase. Contraction time, half-relaxation time, and twitch duration were normal after 4 days of treatment. The resting membrane potential was significantly decreased during treatment. The passive properties of the muscle membrane were unaffected. The overshoot, amplitudes, and rate of depolarization of indirectly elicited action potentials were all decreased on Day 1 of triamcinolone acetonide treatment but these parameters returned to normal by Day 4. The arithmetic mean frequency and the log frequency of miniature endplate potentials increased during treatment but the increase was not significant until Day 4. The average miniature endplate potential amplitude significantly increased during treament, but the modal and median amplitudes were unaffected. In high Mg 2+ solutions (15 m m) quantal content remained essentially the same as control, and the quantal size decreased. In curarized preparations (400 ng/ml) both quantal content and size were the same in controls and treated rats.