The bimodal effect of cholinergic blocking agents on the human parotid gland deprived of parasympathetic control.

Intense salivatory reactions to atropine appear only at the second and are completely at the third stage of the postdenervational syndrome. Muscarinic receptors, emerging at these stages of denervation and causing paradoxical reactions to cholinolytics, differ from those which emerge at the first stage of denervation and from those blocked with atropine. A classical antagonist, atropine is able to discriminate between heterogenous subpopulations of these receptors, emerging at various stages of denervation. The denervated parotid gland presents, an evolving system in terms of muscarinic receptors. Atropine discriminates between the highest levels in the development of those structures and the lowest ones, since for the former it plays the role of an antagonist, and for the latter the role of an agonist.