The effect of noradrenergic receptor blocking agents on 5-hydroxytryptamine turnover in the brain of rats

Phenoxybenzamine (PB), phentolamine (PT) and aceperone (AC) in doses of 25 and 50 mg/kg increased cerebral noradrenaline (NA) turnover so these doses were regarded as blocking brain NA receptors. PB (50 mg/kg), PT (50 mg/kg) and AC (25 and 50 mg/kg) accelerated also the turnover of brain 5-HT. PT in a dose of 25 mg/kg counteracted deceleration of 5-HT turnover induced by clonidine but not by quipazine. Almost the same extent of decrease in 5-HIAA concentration after quipazine was observed in controls as in the rats pretreated with NA blockers in a dose of 25 mg/kg. On the contrary PT given in a dose of 50 mg/kg antagonized significantly the effect of quipazine. The results indicate that NA blockig agents given in lower doses do not affect the 5-HT system, however after higher doses such effect is possible.