Decreased brain serotonergic activity after acute propranolol.

Acute propranolol reduced the synthesis rate of serotonin in several rat brain structures (hypothalamus, midbrain, pons, frontal cortex and medulla oblongata). Both optical isomers of propranolol were tested. From our results it may be concluded that both the beta-blocking property and the local anaesthetic action of the drug could be involved in its inhibitory effect, except in hypothalamus where only the levorotating isomer was effective. Our results suggest the possibility of a noradrenergic influence on brain serotonergic neurons.