Guanidine and neuromuscular transmission. II. Effect on transmitter release in response to repetitive nerve stimulation.

The effect of guanidine on the neuromuscular transmission in human intercostal and mouse diaphragm muscle in vitro during repetitive nerve stimulation was studied. The drug greatly increased the release of acetylcholine (ACh) quanta by nerve impulses at low frequencies of nerve stimulation and at the beginning of tetani at high frequencies of stimulation. The effect was shown to be produced by an increase in fractional release from an unchanged store of ACh quanta available fro immediate release. This seems to explain why guanidine has a poor therapeutic effect in myasthenia gravis but a good effect in the myasthenic syndrome.