Non-adrenergic, non-cholinergic salivary secretion in the ferret

Secretion of parotid and submandibular saliva evoked by electrical stimulation of the parasympathetic nerves occurred in the presence of adrenergic and cholinergic blocking agents. The 'atropine-resistant' response amounted to about 30% in the submandibular gland and to about 5% in the parotid gland as compared to the response before administration of antimuscarinic agents. The 'atropine-resistant' secretion was found at relatively high frequencies, and the latency between the start of the stimulation and the onset of secretion was long. Upon long-lasting stimulation the 'atropine-resistant' secretion decreased rapidly and markedly. The tachykinins substance P (SP) and substance K, injected I.V., evoked flow of saliva from both glands. Given singly, exogenous vasoactive intestinal peptide (VIP) caused no salivary flow. However, it enhanced the tachykinin-evoked secretory response. The response to SP was also enhanced when I.V. injections of this peptide were combined with nerve stimulation, even at subthreshold frequencies for secretion, in the presence of the autonomic receptor blockers. Both tachykinins and VIP are putative transmitters involved in mediating the 'atropine-resistant' secretory response.