The effect of DL-5-hydroxytryptophan (5-HTP) on plasma prolactin in pituitary stalk sectioned rats

5-HTP (5 mg/100 g body weight), a precursor of serotonin, was administered intravenously to pituitary stalk sectioned rats. Plasma prolactin levels were initially increased 30 and 60 min after the injection of 5-HTP and thereafter decreased. Pituitary prolactin content was decreased 60 min after the stalk section as compared to those seen following sham operation. The treatment of 5-HTP induced a moderate increase in pituitary prolactin content in the stalk sectioned rats. In order to confirm the complete disconnection of pituitary stalk after the operation, 2.5 micrograms of dopamine hydrochloride was given into the lateral ventricle of stalk sectioned rats. Plasma prolactin did not change following the administration. Our results demonstrate that 5-HTP acts either directly at the pituitary level or via some mechanism yet to be determined.