Effects of the (+) and (-) enantiomers of the antidepressant drug tianeptine on 5-HTP-induced behaviour.

The effects of the (+) and (-) enantiomers of the antidepressant drug tianeptine (5, 10, 20 mg/kg, i.p.) on wet dog shakes (WDS) and faecal pellet production induced by concurrently administered 5-hydroxytryptophan (5-HTP, 100 mg/kg, i.p.) given 30 min after carbidopa (25 mg/kg, i.p.) were investigated in rats. WDS scores peaked approximately 1 hr after giving 5-HTP and gradually declined over the next 2 hr. (-)-Tianeptine dose-dependently and significantly inhibited WDS. Inhibition became less marked with time after administration, but remained significant over the 3 hr period after the 10 and 20 mg/kg doses and during the first 40 min after the 5 mg/kg dose. (+)-Tianeptine caused slight inhibition without dose-dependence and slightly increased net inhibition when added to the (-) isomer (10 mg/kg). The induction of faecal pellet production by 5-HTP was significantly and dose-dependently inhibited by (-)-tianeptine. The (+) isomer neither altered this effect of 5-HTP nor its inhibition by (-)-tianeptine. Results show that inhibition of 5-HTP-induced WDS and faecal pellet formation by tianeptine was almost completely dependent on the (-) isomer.