Electrophoretic analysis of rat parotid salivary protein composition: investigation of the parasympathetic atropine-resistant secretion.

Rats pretreated with atropine and adrenoceptor antagonists show secretion of saliva upon electrical stimulation of the parasympathetic nerve of the parotid gland. The protein composition of this secretion has been analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and compared with the protein profiles obtained with secretions evoked by parasympathetic stimulation (in the absence of atropine) or infusion of bethanechol with or without vasoactive intestinal peptide (VIP, a probable transmitter conveying parasympathetic secretory impulses). The SDS-PAGE patterns were highly reproducible for an individual rat although minor differences were detected between different rats. The method requires only microlitre volumes of unconcentrated rat saliva and thus is ideal for monitoring sequential aliquots collected from the same rat. The SDS-PAGE patterns indicated (i) little change in the protein profile during prolonged stimulation, (ii) a similar profile with parasympathetic stimulation or infusion of bethanechol, and (iii) a quantitative, rather than qualitative, response to administration of atropine (during parasympathetic stimulation) or VIP (during bethanechol infusion). Thus, the salivary protein composition associated with non-adrenergic, non-cholinergic (NANC) secretion appears similar to that evoked in response to parasympathetic nerve stimulation in the absence of muscarinic receptor blockade.