Transmitter release modulated by isoprenaline in the dog isolated mesenteric vein.

1. The effects of isoprenaline on the release of transmitter substances from perivascular adrenergic nerves were estimated from the excitatory junction potential (ejp) and outflow of noradrenaline in the dog mesenteric vein. 2. Isoprenaline increased the ejp amplitude and decreased the evoked release of noradrenaline. Yohimbine potentiated the former and converted the latter to an increased outflow. 3. Therefore, stimulation of prejunctional beta-adrenoceptor by isoprenaline increases the release of noradrenaline from perivascular adrenergic nerves. 4. Possible involvement of prejunctional alpha-adrenoceptors in the isoprenaline-induced modulation of transmitter release was also suggested.