Biphasic Effect of 1, 1-dimethyl-4-phenylpiperazinium Iodide (DMPP) on the Guinea-pig Distal Colon

1. Effect of DMPP on the contractile activity of guinea-pig distal colon were investigated in normal solution and in various autonomic blocking drugs. 2. Biphasic response was produced by DMPP and the effect of DMPP was blocked by tetradotoxin. The initial contraction in response to DMPP was diminished in physostigmine. 3. The effect of DMPP in guanethidine was nearly similar to that in contral. 4. It is concluded that DMPP stimurated the cholinergic excitatpry neurones in enteric plexus and produced the initial contraction. The relaxation by DMPP may due to stimulating action of DMPP on non-adrenergic inhibitory neurones.