Train-of-four as an index of neuromuscular block in cats: changes induced by atropine.

1. The present study reevaluates the effect of atropine on the rate of recovery from tetanic fade caused by intraarterial administration of neostigmine or antinicotinic agents in cat anterior tibial muscle preparations submitted to a train-of-four (TOF) pattern of nerve stimulation. The study also compares the sensitivity of the TOF and tetanic responses as indices of residual nondepolarizing block. 2. Neostigmine, hexamethonium and d-tubocurarine all produced short-lived TOF fade. Both single and TOF twitches were increased by neostigmine and depressed by the antinicotinic agents. 3. Prior administration of atropine reduced the TOF fade induced by the antinicotinic drugs but potentiated that caused by anticholinesterase drugs. 4. These results indicate that TOF fade is not the most sensitive index for studying neuromuscular blockade when drugs other than neuromuscular blockers are also present.