SUBTYPE OF THE MUSCARINIC RECEPTOR THAT MEDIATES SALIVARY SECRETION IN THE RAT SUBLINGUAL GLAND

The subtype of the muscarinic receptor that mediates salivary secretion in the rat sublingual gland was characterized by use of agonists, carbachol (CAR) and McN-A-343, and antagonists of various types. CAR elicited a long-lasting flow of saliva, and the rate of secretion increased in a dose-dependent manner. By contrast, McN-A-343 did not elicit any significant salivation even at doses as high as 1 mg kg-1. When an antagonist at a dose of 1 mg kg-1 was-injected i.v. 30 min prior to administration of CAR at a dose of 30 mug kg-1, the dose that inhibited, by 50% the sialogogic action of CAR, was 1.9 mug kg-1 for atropine, 4.1 mug kg-1 for 4-DAMP and 205 mug kg-1 for pirenzepine. However, pretreatment with AF-DX-116, phentolamine, propranolol or hexamethonium at a dose of 1 mg kg-1 did not have any significant inhibitory effect. The results suggest that the muscarinic receptors that mediate secretion of saliva from the rat sublingual gland are of the M3 subtype.