Evidences for alpha excitatory action of catecholamines on the electrical activity of the guinea-pig stomach

Effects of catecholamines and their inhibitors on the electrical activity of the smooth muscle of the guinea-pig stomach were studied by using pressure electrodes. The spontaneous electrical activity of antrum and corpus preparations consisted of slow waves with or without superimposed spikes. In quiescent fundus preparations, the spike activity and slow waves were generated by TEA. Catecholamines (noradrenaline, isoprenaline and adrenaline) suppressed or blocked the spike discharges and the generation of slow waves. However, the spike activity was enhanced at a higher concentration of phenylephrine in the antrumand fundus preparations. Inhibitory responses of the smooth muscles from whole regions to adrenaline, noradrenaline or isoprenaline were antagonized by propranolol or DCI but not by phentolamine or phenoxybenzamine. Therefore, inhibitory actions of these amines appear to involve beta-adrenoceptors. After treatment with tetrodotoxin, noradrenaline and isoprenaline blocked the spike activity and the generation of slow waves. Phenylephrine or adrenaline potentiated the spike activity in the presence of tetrodotoxin. After treatment with DCI or propranolol, phenylephrine potentiated the spike activity of the antrum and fundus preparations. These excitatory effects were antagonized by phentolamine or phenoxybenzamine. It is concluded that excitatory actions of these amines are mediated by alpha-adrenoceptors rather than via a nervous pathway.