ATROPINE AND NEUROMUSCULAR FADE IN THE MOUSE PHRENIC NERVE-DIAPHRAGM

Purpose: These studies were intended to resolve the conflict between t he reasonable inference from the scientific literature that atropine m ight alter neuromuscular fade and the expectation from informal clinic al experience that it does not. Methods: We examined the effect of a h igh concentration of atropine (20 mu M) on moderate neuromuscular bloc k and fade produced by d-tubocurarine (dTC). Isometric twitch tension was measured in the mouse phrenic nerve-diaphragm preparation. In one set of experiments, the phrenic nerve was stimulated with trains of 5 pulses at 10 Hz every second. Block and fade were measured in two grou ps, control and with atropine (n = 6 each). In another set of experime nts, the phrenic nerve was stimulated with standard train-of-four stim ulation (TOF, 4 pulses at 2 Hz every 11.5 seconds). Block and fade wer e measured first in a control period and then in a treatment period wi th either saline (n = 4) or atropine (n = 4). Results: During 10 Hz tr ain stimulation, atropine had no significant effect on either the bloc k of the first twitch (control. 62 +/- 17; atropine: 75 +/- 4) or fade (control: 55 +/- 12: atropine; 57 +/- 14) produced by dTC. Similarly, atropine did not differ significantly from saline in altering dTC-ind uced block of first twitch (saline: 99.5 +/- 14; atropine 92.5 +/- 9.6 % control) or fade (saline 119 +/- 50; atropine 102 +/- 30% control) d uring TOF stimulation. Conclusions: While atropine may alter ACh relea se under some conditions, its action is not great enough to alter eith er block or fade.