Whole blood serotonin and tryptophan levels in Tourette's disorder: Effects of acute and chronic clonidine treatment

Abstract

Whole blood serotonin (WB5HT) and tryptophan (WBTRP) levels were studied in 20 patients (aged 8 to 45 years) with Tourette's disorder under medication-free baseline conditions and following acute and chronic clonidine treatment. Compared to 87 normal controls, Tourette's disorder patients had lower mean baseline WBTRP levels (mean ± SEM: Tourette's, 5993 ± 304 ng/ml vs. 6822 ± 169 ng/ml; p <.03). No significant differences in mean baseline WB5HT levels were found. Three hours after an acute dose of clonidine (2.5 – 5.1 ug/kg, p.o. at 9:00 A.M.), no mean differences were observed (baseline vs. post 3 hours) in WB5HT or WBTRP levels. However, following chronic treatment (> 3 weeks) with clonidine (3–8 ug/kg/day, p.o.), WB5HT levels were increased in 9 of 14 Tourette's disorder patients. The mean increases in WB5HT levels following chronic clonidine treatment were significant when WB5HT levels were expressed per 10 9 platelets. (mean ± SEM: baseline, 471 ± 45 ng/10 9 platelets vs. chronic, 697 ± 82 ng/10 9 platelets, p = .02). No mean differences in WBTRP levels were observed after chronic clonidine treatment. These findings are discussed in light of a proposed intermediary role of 5HT systems in the mode of action of clonidine in the treatment of Tourette's disorder.