SECRETORY INTERACTIONS BETWEEN THE SYMPATHETIC AND PARASYMPATHETIC INNERVATIONS OF THE SUBMANDIBULAR-GLAND IN THE ANESTHETIZED CAT

Interactions between the sympathetic and parasympathetic innervations of the submandibular gland have been investigated in the anaesthetized car. At low frequencies of chorda lingual (parasympathetic) stimulati on, simultaneous stimulation of the ascending cervical sympathetic ner ve in bursts (20 Hz for 1 s at 10 a intervals) increased the Row Of su bmandibular saliva, but the effect was never more than additive. The o utput of protein was consistently reduced by simultaneous stimulation of both the sympathetic and parasympathetic innervations, below that e voked by stimulation of either alone. Sympathetic stimulation was more effective than parasympathetic stimulation in promoting the secretion of tissue kallikrein and peroxidase in the submandibular saliva. The output of the latter enzyme, in response to sympathetic stimulation, w as significantly reduced by simultaneous stimulation of the parasympat hetic innervation at frequencies greater than 1 Hz, but nevertheless e xceeded the amount secreted during chorda stimulation alone. Thus, thi s protocol provided no evidence of synergy between the two divisions o f the autonomic nervous system with respect to any submandibular secre tory function that was recorded. However, following the administration of a small dose of atropine (2-15 mu g kg(-1) I.V.), sufficient to bl ock secretion during chorda stimulation alone, the flow of saliva, in response to sympathetic stimulation, was potentiated when superimposed on a background of parasympathetic stimulation at all frequencies tha t were employed. This effect was abolished by larger doses of atropine , indicating that it was dependent upon activation of muscarinic recep tors, only some of which could have been blocked by the initial dose.