Protection by nitric oxide of morphine-induced inhibition of rat submandibular gland function

The effects of morphine, L-arginine (nitric oxide precursor) and L-NAME (nitric oxide synthesis inhibitor) and their concurrent therapy on rat submandibular secretory function were studied. Pure submandibular saliva was collected intraorally by micro polyethylene cannula from anaesthetized rats using pilocarpine as secretagogue. Single intraperitoneal injection of morphine (6 mg kg(-1)) to rats induced significant (P < 0.01) inhibition of salivary flow rate (28%), total protein (12%) and calcium concentrations (27%). Sodium output was increased (23%, P < 0.01). Single intraperitoneal administration of L-arginine (100 tug kg(-1)) and L-NAME (10 mg kg(-1)) affected salivary gland function. Saliva flow rate was reduced by L-NAME (23%, P < 0.01). The total protein concentration of saliva was increased by L-arginine (21%, P < 0.05) and decreased by L-NAME (19%, P < 0.01). Calcium concentration of saliva was increased by L-arginine (25%, P < 0.01) and reduced by L-NAME (21%, P < 0.01). In combination treatment, L-arginine prevented (P < 0.01) morphine-induced reduction of flow rate while L-NAME potentiated it (P < 0.01). The secretion of total protein and calcium were influenced in a similar trend by concurrent therapy. L-NAME potentiated morphine-induced decrease of total protein and calcium concentrations (P < 0.01) while L-arginine restored (P < 0.01) them to levels close to control and morphine groups respectively. It is concluded that morphine inhibits salivary gland function and nitric oxide (NO) plays a positive role in this system. Also it is confirmed that morphine inhibitory effects on submandibular function are somewhat restored by L-arginine and expanded by L-NAME. The modulatory effect of the L-arginine/NO system on salivary gland function is suggested. (C) 2002 Elsevier Science Ltd.