Effects of Sympathetic Nerve Stimulation in the Presence of a Slow Parasympathetic Secretion in the Parotid and Submaxillary Glands of the Rabbit

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Abstract
Sympathetic secretory responses from the parotid and the submaxillary glands of the rabbit were studied; sympathetic excitation occurred either alone or during a slow parasympathetic background secretion, imitating the resting secretion normally present. The fairly rapid sympathetically evoked flow of saliva from the parotid gland was, in the background secretion, further increased and obtained at low frequencies, which at sympathetic stimulation alone were subthreshold. The effects, which could be repeated with sympathomimetic drugs [epinephrine, phenylephrine dihydroergotamine] in a pilocarpine induced secretion, were abolished by .alpha.- and .beta.-adrenoceptor blockade [isoprenaline, phenoxybenzamine, practolol] in combination. The submaxillary gland gave a very scanty secretion on sympathetic excitation, the effects being mediated via .beta.-adrenoceptors. The responses were not increased in a background secretion but the main effect of sympathetic activation was to retard the salivary flow. The retardation was attributed to vasoconstriction accompanying sympathetic excitation. Eliminating the vasoconstrictor responses, while retaining the sympathetic secretory effects, did not reveal any increase of the sympathetic salivary responses in the submaxillary gland.