Effects of endothelin on submandibular salivary responses to parasympathetic stimulation in anaesthetized sheep

Submandibular responses to stimulation of the parasympathetic chorda tympani nerve have been investigated in anaesthetized sheep before, during and after an intracarotid infusion of endothelin, which reduced the blood flow through the gland by 56+/-5%. Stimulation of the peripheral end of the chorda tympani nerve produced a frequency-dependent increase in the flow of submandibular saliva, and in sodium, potassium and protein output. The reduction in submandibular blood flow, which occurred in response to endothelin, was associated with a decrease in the flow of saliva at all frequencies tested amounting on average to 44+/-6% (P<0.01). The flow of saliva was linearly related to the blood flow before and after endothelin. Both parameters were also linearly related during the infusion of endothelin and the regression lines were parallel. Salivary sodium concentration was significantly increased at the lower frequencies (1 and 2 Hz). Protein output was generally reduced but the difference only achieved statistical significance during stimulation at 1 Hz (P<0.01). Thus, submandibular secretory responses to parasympathetic stimulation are significantly attenuated by reducing the blood flow through the gland in this way.