Pfeuffer-Friederich_1987_Eur.J.Pharmacol_136_225

The effects of 5-hydroxykynuramine (5-OH-K) and of 3-(2-amino-5-hydroxyphenyl)-propaneamine (AHPP) on spontaneous and electrically evoked release of [3H]acetylcholine were studied in the guinea-pig myenteric plexus longitudinal muscle preparation preincubated with [3H]choline. 5-OH-K caused a concentration-dependent increase in spontaneous [3H]acetylcholine release (EC50 5.3 microM). This effect was diminished in the presence of a desensitizing concentration of 5-hydroxytryptamine (5-HT). AHPP (1-100 microM) did not affect the spontaneous outflow of [3H]acetylcholine. The electrically evoked release of [3H]acetylcholine was significantly reduced in the presence of 100 microM of either 5-OH-K or AHPP. Metitepine did not antagonize the inhibition, which suggests that 100 microM of either compound non-specifically depressed the evoked release. It is concluded that 5-OH-K is inactive at the release-inhibitory 5-HT1 receptor, but is a potent agonist at the M receptor of myenteric neurons.