Inhibitory effects of atropine and adrenergic antagonists on the changes in autonomic receptors and cyclic nucleotides of rat parotid and submandibular glands caused by sympathetic nerve stimulation.

The changes in cyclic AMP (cAMP) concentration and density of beta-adrenoceptors caused by electrical stimulation of the sympathetic innervation to parotid and submandibular glands of rat did not occur when the alpha- and beta-adrenergic antagonists, phentolamine, and propranolol were administered 20 min prior to initiation of stimulation. They also did not occur when phentolamine, the beta-adrenergic antagonist, was administered alone prior to nerve stimulation, indicating that beta-adrenoceptors mediate these effects. Simultaneous administration of the alpha- and beta-antagonists also prevented the changes in densities of muscarinic receptors and cGMP concentrations usually induced by sympathetic nerve stimulation. Also, the changes in muscarinic receptors and cGMP did not occur when atropine was administered prior to nerve stimulation, nor did they occur with simultaneous administration of atropine, phentolamine + propranolol; with phentolamine alone, or propranolol alone, the effects were blocked to a large extent. Secretion was inhibited completely when both adrenergic antagonists were present during nerve stimulation, but flow rate was unchanged when atropine was present. The changes in both beta-adrenoceptors and muscarinic receptors reflect a desensitization caused by prolonged exposure to neurotransmitters released when the sympathetic nerve is stimulated. The changes are prevented when either atropine or adrenergic antagonists are present during nerve stimulation.