ON THE EXISTENCE OF PARASYMPATHETIC MOTOR NERVES TO THE SUBMAXILLARY GLAND OF THE DOG

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Abstract
Duct pressure and salivary flow were recorded in submaxillary glands of anesthetized dogs, to study whether parasympathetic stimulation caused effects referable to activity in myoepithelial cells. At fairly low frequency of stimulation, e.g., 3 Hz, the pressure curve had 2 distinct components, with an initial steep and a secondary gradual rise. It resembled that obtained on sympathetic stimulation, where the 1st phase is ascribed to myoepithelial contracton, the 2nd phase to secretion. When parasympathetic stimulation ceased, there was first a steep fall, then a more gradual decline of the pressure. The steep fall was of the same magnitude as the steep rise; both increased with the frequency of stimulation. The size of the initial fall was fairly independent of the pressure level from which it started. Such a steep fall did not occur subsequent to parasympathetic stimulation if the myoepithelial cells were already in a state of strong contraction caused by sympathetic impulses or bradykinin. The phase of steep fall was inferred to be due mainly to relaxation of contracted myoepithelial cells, the following decline to back-flow of fluid into the gland. The salivary flow rate was highest at the beginning of a period of parasympathetic stimulation, particularly if the duct system was well filled and the saliva thin. Myoepithelial contraction had initially expelled saliva. A brief period of parasympathetic stimulation while a slow basal secretion at constant rate was going on accelerated this flow, and afterwards there was a transient deceleration of the flow. Acceleration was attributed partly to myoepithelial contraction, mainly to superimposed secretion; retardation was due to myoepithelial relaxation. The effect appeared independently of the way in which the basal flow was evoked, and the retardation resembled that seen after sympathetic stimulation or bradykinin.