Synergism in the autonomic regulation of parotid secretion of protein in sheep

1. Stimulation of the cervical sympathetic nerve continuously at 2 Hz, or in bursts of 1 s at 20 Hz every 10 s, for 5 min doubled the resting flow of parotid secretion in anaesthetized sheep and increased its concentration of protein. It also caused a significant increase in the concentration of potassium and decreased that of sodium: these latter effects were linearly inversely related. 2. Stimulation of the parotid nerves (the parasympathetic innervation) continuously at 2 Hz increased the flow of parotid secretion over 15-fold which was significantly more than that which occurred in response to stimulation in bursts at 20 Hz. However, the latter pattern of stimulation significantly increased the concentration of protein in the saliva, which was not altered by stimulation at 2 Hz continuously. 3. Simultaneous stimulation of both the parotid and sympathetic nerves at 20 Hz in bursts substantially increased the output of protein from the gland, above that recorded in response to stimulation of either alone, without potentiating either the volume of secretion produced or the outputs of sodium or potassium. 4. The output of protein was also potentiated when both nerves were stimulated simultaneously at 2 Hz continuously but this pattern of stimulation elicited the secretion of a significantly smaller amount of protein. 5. All parotid responses to stimulation of the parotid nerves, either continuously at 2 Hz or in bursts at 20 Hz, were abolished by atropine (greater than or equal to 0.5 mg kg-1 I.V.), as was potentiation of protein secretion during combined stimulation with the sympathetic innervation. 6. Stimulation of the parotid nerves in bursts at a higher frequency (60 Hz for 1 s at 20 s intervals) elicited a sparse flow of parotid saliva in atropinized animals without significant increase in protein output, with or without simultaneous stimulation of the sympathetic innervation. 7. The results of these experiments show that secretion of protein by the parotid gland, in response to stimulation of the parasympathetic innervation, depends on the pattern of stimulation and is potentiated by concomitant stimulation of the sympathetic innervation in anaesthetized sheep.