Serotonergic stimulation of pituitary-adrenocortical activity in rats: evidence for multiple sites of action

5-Hydroxytryptophan (5-HTP) elevated serum corticosterone concentrations when administered either intraperitoneally (i.p.) or intraventricularly. Inhibition of aromatic L-amino acid decarboxylase outside of the blood-brain barrier antagonized the corticosterone response, but only when the 5-HTP was given i.p. Stimulation of the pituitary-adrenocortical system by fenfluramine was not affected by 5,7-dihydroxytryptamine pretreatment, whereas the stimulation produced by quipazine administration was blocked by lesions of the basomedial hypothalamus. These results suggest that serotonergic drugs can act at multiple sites (i.e., both central and peripheral) to evoke a pituitary-adrenocortical response.