The Effects of Tyramine on Salivary Flow Rate and Protein Secretion by Rat Submandibular Glands

The effects of different doses of p-tyramine injected i.v. and i.p. on salivary flow rates and proteins secreted by the submandibular glands of rats were studied with and without various types of autonomic blockers and two enzyme inhibitors. The salivary flow rates and the amounts of protein secreted progressively increased with increasing doses injected both i.v. and i.p., whereas they were dramatically reduced with all autonomic blockers except the lowest doses of β-blockers, atropine, and yohimbine. Salivation in response to p-tyramine injected i.v. and i.p. was completely abolished by simultaneous injections of both prazosin and propranolol. The concentration of protein was not dose-dependent and was not reduced by yohimbine and phenoxybenzamine at almost all doses used. However, prazosin significantly increased the protein concentration. Protease activities were dose-dependent but were significantly reduced with a-blockers other than yohimbine, and with most β-blockers. The proteins secreted in response to p-tyramine at all doses injected i.v. and i.p. were of the a-type except with the lowest dose injected i.p. However, the a-type was completely replaced by the β-type in the presence of all a-blockers except yohimbine, but not with β-blockers, atropine, or two enzyme inhibitors. Pargyline, a monoamine-oxidase inhibitor, but not disulfiram, a dopamine-β-hydroxylase inhibitor, affected all parameters except the type of protein. Thus, p-tyramine may activate both the α₁- and β₁adrenoceptors in the submandibular glands of rats directly or indirectly.