Inhibitory and excitatory effects of sympathomimetic amines on muscle strips from the stomach of the guinea-pig.

1. Responses of muscle strips from the stomach of the guinea-pig have been recorded. Sympathomimetic amines cause inhibitory, motor or biphasic responses.2. The motor components of the responses of the preparations were greatly enhanced by the removal of the mucosal layers.3. The inhibitory responses to isoprenaline, noradrenaline and phenylephrine were antagonized by propranolol or by sotalol. The inhibitory responses to noradrenaline and phenylephrine but not isoprenaline were antagonized by phentolamine. Therefore, both alpha- and beta-adrenoceptors may subserve inhibition.4. The motor responses to noradrenaline and phenylephrine were often potentiated by propranolol or sotalol and were antagonized by phentolamine. Therefore, motor responses to sympathomimetic amines appear to involve alpha-adrenoceptors.5. The responses to sympathomimetic amines and their antagonists were not modified by hyoscine or by tetrodotoxin. It is concluded that the adrenoceptors mediating the responses recorded from these preparations are located on the smooth muscle cells rather than on a nervous pathway.