[The effect of temperature on the action of several neuromuscular blocking agents in vitro]

The effects of lowered muscle temperature on the action of neuromuscular blocking drugs have been investigated so far from basic or clinical aspects, but the results of these studies are conflicting probably because of the differences of methods and/or species of the animals. The effects of hyperthermia on neuromuscular junction are not yet known. To clarify the effects of variations in temperature on the neuromuscular blockade produced by each of the 5 neuromuscular blocking agents in current use (vecuronium, pancuronium, pipecuronium, dTc, SCC), we used the rat phrenic nerve-hemidiaphragm preparation and compared the ED50 at each temperature with that at 37 degrees C. The temperatures examined were 17 degrees C, 27 degrees C, 32 degrees C, 37 degrees C, 40 degrees C, and 42 degrees C. As to vecuronium and pancuronium, potentiating effects were observed with both hypothermia and hyperthermia. In contrast, pipecuronium was not affected by the change of temperature from 27 degrees C to 42 degrees C. SCC was only potentiated at the temperatures of 27 degrees C and 17 degrees C, while dTc showed a biphasic phenomenon by hypothermia. The ED50's of dTc at 37 degrees C and 27 degrees C were twice as large as that of at 32 degrees C, but ED50 of 17 degrees C was significantly lower than that of 37 degrees C. Hyperthermia did not modify the neuromuscular blockade by dTc.