Effect of tryptophan administration on serotonin and 5-hydroxyindoleacetic acid content in the brainstem of Lilly 110140-pretreated rats

Adult male Sprague-Dawley rats were divided into 3 groups. One group was pretreated with Lilly 110140 (10 mg/kg) 27 hours and again 3 hours before sacrifice while a second group received Lilly 110140 only 3 hours before sacrifice. The third or control group received only equivalent volumes of saline. Animals from each group were administered 25 mg/kg L tryptophan intraperitoneally (i.p.) 0, 30, 60 or 90 minutes before sacrifice. Equivalent elevations in serum and also brainstem tryptophan content were observed in all three groups with the peak observed at 30 minutes. Brainstem serotonin content was significantly elevated in both groups of Lilly 110140-pretreated rats but not in the control group. Brainstem 5-hydroxyindoleacetic acid was significantly elevated after tryptophan administration in the control and the 3 hour and 27 hour, Lilly 110140-pretreated groups but not in the 3 hour Lilly 110140 pretreated group. The results indicate that neither 3 or 3 hours and 27 hours of Lilly 110140 pretreatment appreciably affects the increase in brainstem serotonin synthesis induced by the i.p. administration of 25 mg/kg of L tryptophan.