Release of [3H]noradrenaline induced by 5-hydroxytryptamine from cat pial arteries.

Pial arteries of cats were used to analyse the effects of 5-hydroxytryptamine (5-HT) on the release of [3H]noradrenaline. To achieve this the vessels were preincubated with [3H]noradrenaline and the effect of different concentrations of 5-HT (10(-6), 10(-5), 10(-4) M) on the release of tritium was studied. 5-HT elicited release of radioactivity in a dose-dependent manner. Removal of both superior cervical sympathetic ganglia 15 days before the experiment of pretreatment of the animals with reserpine (3 mg kg-1, total dose) produced a significant decrease in the outflow of tritium induced by 5-HT. In these arteries, the amount of radioactivity retained at the end of the experiment was much diminished. Cocaine (10(-6) M) caused a significant decrease in the tritium efflux induced by 5-HT (1"0(-5) M). These results show that 5-HT has an indirect adrenergic effect in the pial arteries of the cat only at high doses of 5-HT, and confirm that sympathetic innervation of these vessels mainly comes from the superior cervical ganglia.