Some mechanism which may modulate noradrenaline release in guinea-pig isolated ileum

Guinea-pig isolated ileum pre-incubated with [3H]noradrenaline, released 3H-label during coaxial stimulation at 3.2-12.8 Hz. This evoked 3H-overflow seems due to nerve stimulation, and may be frequency-dependent. The 3H-overflow evoked by coaxial stimulation was increased with 2.6 muM phentolamine, reduced at threshold stimulation by 0.56 muM prostaglandin E1, but the tendency for 2.8 muM indomethacin to increase the evoked 3H-overflow was not statistically significant. The results indicate that the release of noradrenaline from guinea-pig ileum may be modulated by activation of presynaptic alpha-adrenoceptors, whereas prostaglandins act mainly at a postsynaptic site to modulate the sympathetic response.