Observations on some actions of ergometrine, noradrenaline and dopamine on the guinea-pig vas deferens and on the rabbit jejunum

[Effects of precursors and metabolites of catecholamines on motricity of isolated rat duodenum. Particular reference to dopamine]

Studying the effects, on the isolated rat duodenum motricity, of ten compounds precursors or metabolites of catecholamines, the following results were obtained: The direct metabolites of epinephrine and norepinephrine (metanephrine, normetanephrine), are either ineffective at concentrations below 5 X 10(-6) M, or weakly inhibitory at higher concentrations. Such inhibitory effects are prevented by alpha- and beta-blockers. 3-methoxy, 4-hydroxyphenylglycol and vanylmandelic acid have no significant effect. The catecholamine precursor, dopamine, the related compounds DOPA, 3 methoxytyramine, and to a lesser extent, 3-O methyl DOPA and homovanillic acid, have excito-motor effects at concentrations ranging mainly from 10(-7) M to 10(-5) M. At higher concentrations, the same compounds frequently exhibit inhibitory effects. The excito-motor effects might be due to a serotoninergic mechanism, since they are suppressed by the serotoninergic blocking agents methysergide and cyproheptadine. Furthermore, in the case of DOPA, we were able to establish a relationship between the excito-motor effects and duodenal serotonin stores. As for the inhibitory effects, they may be prevented by using alpha and beta blocking agents. Dihydroxyphenylacetic acid has no effect on the isolated rat duodenum motricity. The fact that dopamine and related compounds may have excitomotor effects at some concentrations, correlated with some physiopathological observations in man and animal allows some considerations about the eventual role of dopamine on intestinal motricity.

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.