Low-frequency subthreshold sympathetic stimulation augments maximal reflex parasympathetic salivary secretion in cats

Abstract

Electrical stimulation of the peripheral cut end of the cervical sympathetic trunk for 3 min at frequencies < 1 Hz with pulses of 2-ms duration at supramaximal intensities did not elicit any salivary secretion, but an increase of stimulus frequency over the range 2-10 Hz produced progressively greater salivary secretion, the maximum volume of salivary secretion being evoked at 10 Hz. Frequency-dependent augmentation of parasympathetic reflex submandibular salivary secretion occurred when the lingual nerve was stimulated during repetitive sympathetic stimulation (at frequencies of 0.1-2 Hz) in our sympathectomized cats. The augmentation was found to be linearly related to sympathetic stimulus frequency (regression line calculated by method of least squares; r = 0.939, P < 0.01). This augmentation was abolished by prior treatment with the beta-adrenoceptor blocking drug propranolol (1 mg/kg, P < 0.01 vs. before propranolol) but not by the alpha-adrenoceptor blocking agent phentolamine (1 mg/kg), indicating that the augmented response was mediated via an activation of beta-adrenoceptors. The reduction of the augmentation caused by propranolol had diminished 1 h after its administration, showing that the effect was reversible.