AIM To observe if dichlorvos having the direct toxicity on the diaphragm. METHODS Isolated rat diaphragm was directly stimulated
with a home-made double-functional electrode after the
neuromuscular synaptic transmission was blocked with tubercurarine. The
contraction of the rat diaphragm caused in this way had no relation to the neuromuscular synaptic transmission. The direct action of dichlorvos could be observed by its influences on such kind of contraction. RESULTS After the neuromuscular synaptic transmission was completely blocked with tubercurarine, stimulating phrenic nerve was not able to induce the contraction of diaphragm, while directly stimulating diaphram could still result in its contraction. Dichlorvos at the concentration of 0.724 mmol·L -1 began to inhibit the directly-stimulated tetanic-like contraction of the rat diaphragm. At the concentration of 4.34 mmol·L -1, such contraction was inhibited by 80%. At the concentration of 5.79 mmol·L -1, both the tetanic-like and simple contractions were completely inhibited by dichlorvos, pralidoxime could not reduce the inhibition. CONCLUSION Dichlorvos has direct inhibition effect on the diaphragm, which is unrelated to the block of the neuromuscular transmission and the inhibition of acetylcholinesterases.