Release of endogenous 5-hydroxytryptamine from the intermediate lobe of the rat pituitary gland is inhibited by endogenous dopamine.

The release of endogenous 5-hydroxytryptamine (5-HT) from the in vitro incubated neurointermediate lobe (NIL) of the rat hypophysis was measured by HPLC with electrochemical detection. 5-HT release evoked by electrical stimulation of the pituitary stalk from the NIL, but not from the isolated neural lobe (NL) was enhanced in the presence of the dopamine receptor antagonist sulpiride (1 microM). The opiate receptor antagonist naloxone (1 microM) had no effect on the evoked release of 5-HT from the NIL or NL. In conclusion, the release of endogenous 5-HT from the intermediate lobe is under inhibitory control of endogenous dopamine.