Nitric oxide modulates salivary amylase and fluid, but not epidermal growth factor secretion in conscious rats

The involvement of the L-arginine/NO pathway in the control of salivary fluid, amylase and epidermal growth factor (EGF) secretion was investigated in conscious rats. For the collection of saliva, an oesophageal cannula was implanted. To obtain steady secretion, submaximal carbachol background infusion was given. Different treatments included NO synthase inhibitor N(G)-nitro-L-arginine (NOLA; with or without phentolamine, propranolol), L-arginine, D-arginine and NO donor 3-morpholinosydnonimine (SIN-1) administration. Volume, amylase activity and EGF output in the secreted fluid were determined in 30 min mixed saliva samples. Carbachol infusion alone produced a modest, sustained salivary fluid and amylase secretion. NOLA (30 mg/kg) further increased both fluid (p<0.001) and amylase outputs (p<0.001). These latter effects were prevented by L-arginine but not by D-arginine or by phentolamine. Propranolol administration decreased both fluid and amylase secretion below the carbachol plateau, and NOLA did not modify this suppressed secretory rate. SIN-1 did not alter either volume or amylase secretion. Interestingly, NOLA given without carbachol did not modify salivation. Neither carbachol nor NOLA changed salivary EGF output. The present results suggest that the L-arginine/NO pathway has a modulatory role in the cholinergic control of salivary amylase secretion, but not in EGF output. The mechanisms of inhibitory action of NO on salivary fluid and amylase secretion remain to be identified.