Effects of 5-hydroxytryptamine on neuroeffector junction in human pulmonary artery

The effects of 5-hydroxytryptamine on release of norepinephrine and on contraction of smooth muscle in human pulmonary artery were studied. Helical strips were prepared from intraparenchymal arteries removed 3-18 h after death. The strips were labeled with L-[7-³H]norepinephrine and mounted for superfusion and isometric tension recording. Electrical stimulation (10 V, 2 ms, 2 Hz) of the strips increased the release of total radioactivity; this release was blocked by tetrodotoxin. 5-Hydroxytryptamine (10^-5 M) exerted a cocaine-sensitive, indirect sympathomimetic effect on the overflow of norepinephrine from resting strips. This action was not blocked by methysergide. No effect of 5-hydroxytryptamine on release of norepinephrine from electrically stimulated tissue could be demonstrated. 5-Hydroxytryptamine (10^-5 M) also caused contractions of pulmonary smooth muscle, not blocked by phentolamine (10^-5 M) but mediated in part through methysergide-sensitive 5-hydroxytryptamine receptors.