Relative secretory contributions of the three major salivary glands of the rat in response to substance P and super-sensitivity

In vivo salivation in the rat in response to a range of intravenous doses of substance P was studied. The ducts of the parotid, submandibular and sublingual glands were cannulated. The secretory threshold dose of substance P, in microgram/kg, was 0.05-0.1 in the submandibular glands, 0.2 in the parotid glands and 0.2-0.5 in the sublingual glands. The maximal secretory response in all three types of glands was obtained at a dose level of 5-10 micrograms/kg. The total amount of saliva secreted at this dose level from the three pairs of glands was calculated to about 300 mg; the submandibular glands were responsible for 65 per cent, the parotid glands for 32 per cent and the sublingual glands for 3 per cent. Parasympathetic decentralization but not sympathetic denervation caused the sublingual glands to develop a super-sensitivity to substance P. The secretory effect of substance P was not exerted via cholinergic, alpha-adrenergic or beta-adrenergic receptors.