EFFECTS OF NICOTINE, DIMETHYLPHENYLPIPERAZINIUM AND TETRAMETHYLAMMONIUM ON SMOOTH MUSCLES FROM FELINE AND HUMAN GASTRIC CORPUS

Abstract

Both excitatory and inhibitory intrinsic neurons could be found within the gastric wall, both of them receiving innervation from vagal fibres and being sensitive to nicotine. The effects of three nicotine receptor agonists, nicotine, tetramethylammonium (TMA) and 1,1-dimethyl-4-phenylpiperazinium (DMPP), on contractile activity of preparations isolated from feline and human gastric corpus wall were investigated. While DMPP (3.5×10−8to 5.9×10−4m) did not affect either spontaneous contractions or basal tension of isolated preparations from both species, TMA produced concentration-dependent tonic contractions of both circular and longitudinal isolated preparations from human (3.66×10−5to 5.10×10−3m) and feline (6.1×10−7to 2.1×10−3m) stomach. On the other hand, nicotine (4.1×10−8to 7.0×10−4m) produced concentration-dependent relaxation of only circular isolated preparations from feline gastric corpus. The effect of nicotine was sensitive to mecamylamine, and not to pancuronium, while the effect of TMA was sensitive to both mecamylamine and pancuronium. Although in our experiments DMPP had no effect, its excitatory action on gastric intrinsic neurons through the hexamethonium-insensitive pathway had already been described. The results of our study suggest that two different types of ganglion nicotine receptor exist together within the wall of feline stomach: (1) type NN1which is involved in relaxation and is sensitive only to nicotine and mecamylamine, and not to DMPP, TMA and pancuronium; (2) and type NN2which is involved in contraction of gastric muscle and sensitive to DMPP, TMA, mecamylamine and pancuronium, and not to nicotine.