A comparison of serotonin (5-HT) blood levels and activity of 5-HT2 antagonists in adjuvant arthritic Lewis and Wistar rats.

The total plasma 5-HT levels of adjuvant arthritic rats were increased in animals of both strains in comparison to healthy controls. The exception was day 1, when the 5-HT plasma level in arthritic Lewis rats was decreased by 77%, but only by 17% in Wistar rats. Treatment with the 5-HT2 receptor antagonist ritanserin caused a significant inhibition of macroscopic arthritis at day 14 in Lewis but not in Wistar rats. The total plasma 5-HT level was significantly decreased by the 5-HT2 antagonists in both strains at various times. 5-HT as an autacoid with effects on the T-lymphocytes and on delayed hypersensitivity reactions might be responsible, at least in part, for strain differences regarding the incidence of secondary lesions in rat adjuvant arthritis.