Effect of sodium nitroprusside on the biophase concentration of D-tubocurarine at the neuromuscular junction.

D-Tubocurarine (DTC) at an intravenous dose of 250 micrograms/kg, or at an intra-arterial dose of 25 micrograms/kg, produced about a 50% block on the twitch tension of the indirectly stimulated tibialis anterior muscle of anaesthetized cats. The DTC-induced neuromuscular block was abolished if it was given intravenously but not intra-arterially, 30 min after the commencement of sodium nitroprusside (SNP) infusion (5 micrograms/kg per min) when there was a maximum decrease in blood pressure. The results indicate that the biophase concentration of DTC at the neuromuscular junction may be decreased as a consequence of the vasodilation induced by SNP leading to a reduced transport of the blocker to the site of action.