Studies on the salivary secretion induced by substance P in perfused submandibular gland of rat.

The purpose of these experiments was to clarify the effects of substance P (SP) on the salivary secretion in comparison with those of autonomic agents. Salivary secretion from rat submandibular gland (SMG) was induced by intravenous infusion into the femoral vein or partial perfusion of SMG with isotonic solution containing SP or autonomic stimulants. Blood and salivary flow rates, and electrolyte concentrations of saliva were measured. The relationship between electrolyte concentrations and salivary flow rate after intravenous infusion of SP was similar to that obtained using parasympathomimetic agents. Salivary flow rates induced by phenylephrine and isoproterenol were significantly increased by the further addition of SP, while the pilocarpine-induced flow rate was not affected. SP alone caused a significant increase in blood flow rate of perfused rat SMG. SP with atropine or phentolamine somewhat increased the blood flow. However, concomitant perfusion of atropine and phentolamine completely inhibited the SP effect. Salivary secretion induced by SP perfusion was reduced by atropine or phentolamine. Both blood flow elevation and salivary secretion induced by SP were reduced with increasing doses of a SP-antagonist. Also blood and salivary flow responses induced by phenylephrine were severely reduced by the SP-antagonist. On the other hand, the salivary secretion induced by pilocarpine was moderately reduced by the SP-antagonist. These results indicate that the salivation and especially the glandular vasodilation induced by SP were partially modified by the autonomic agents.