The depressor effect of dopamine on the electrical and mechanical activities of cat small intestine.

Effects of externally applied dopamine and other adrenergic stimulants on the electrical and mechanical activities of the cat small intestine were observed by using pressure electrodes. DOPA and dopamine reduced the spike and mechanical activities. The effects of dopamine were suppressed by treatment with phentolamine, phenoxybenzamine or propranolol. It seems that beta-response is predominant. Noradrenaline and adrenaline also blocked the spike generation and depressed the mechanical activity. Inhibitory actions caused by noradrenaline and adrenaline were blocked by adrenergic blockers. However, no significant effects of normetanephrine and metanephrine were detected. Dose-response curves for acetylcholine with and without dopamine, isoprenaline, phenylephrine and noradrenaline were obtained. The curves with adrenergic stimulants were shifted to higher concentrations of acetylcholine. Possible actions of dompanine were discussed in relation to adrenergic receptors of the cat small intestine. It is concluded that dopamine acts on alpha- and beta-receptors, and separate dopamine receptors could not be proposed by obtianed results.