Opposite effects of antidepressants on unstimulated and stimulated salivary flow

In this study, effects on both stimulated and non-stimulated salivary flow as well as salivary components of different antidepressant drugs were compared. Rats received imipramine (IMI; 10 mg/ml), fluoxetine (FLU; 20 mg/ml) or moclobemide (MOC; 30 mg/ml) by gavage. The drugs were administered 24, 5 and 1 h before saliva collection (sub-acute treatment) or as a once a day treatment for 14 days (chronic treatment). Animals were sedated with thiopental and saliva was collected using pre-weighed cotton balls inserted in the mouth for 1 min before and after pilocarpine stimulus. Pilocarpine-stimulated saliva was also collected for biochemical assays of total proteins, amylase, phosphate and calcium, performed through automated colorimetric methods. Non-stimulated salivary flow was decreased by sub-acute IMI 10 mg/kg treatment. Pilocarpine-stimulated salivary flow was significantly increased by acute treatments with IMI, FLU and MOC in comparison to the control group. The same opposite pattern of effects on non-stimulated and pilocarpine-stimulated salivation was seen after chronic treatment with the antidepressants. Increased levels of calcium following sub-acute treatment with IMI and after prolonged treatment with FLU and MOC were detected. In the assayed samples, phosphate was found to be increased following chronic treatment with FLU or MOC. These results may explain the discrepant effects of the antidepressants on salivation described in pre-clinical and clinical studies.