RELEASE OF [H-3]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 or 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 (10−5 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. 1979 Royal Pharmaceutical Society of Great Britain