Neurally Mediated Increase in Vascular Permeability in the Rat Trachea: Onset, Duration, and Tachyphylaxis

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Abstract
Electrical stimulation of the cervical vagus nerve of rats is known to increase vascular permeability in the trachea. In the present study, we sought to further characterize this neurogenic inflammatory response by defining the relationship between the parameters of electrical stimulation of the vagus nerve and the magnitude of the increase in vascular permeability, by determining the onset and the duration of the increase in vascular permeability, and by assessing the development of tachyphylaxis in response to consecutive periods of vagal stimulation. The extravasation of Evans blue dye in the trachea was used as an index of tracheal vascular permeability. Rats were injected intravenously with dye and their right vagus nerves were electrically stimulated. The rats were then prefused with fixative, their tracheas were removed, and the amount of ex-travasated dye in the tracheas was measured with a spectrophotometer. We found that a vagal stimulus of 5 V and 20 Hz for 15 s increased the amount of dye in the tracheas 5.5-fold compared to controls, that the dye extravasation began within 30 s of the start of vagal stimulation and lasted for 3-5 min, and that tachyphylaxis developed after a stimulus as brief as 15 s and reduced the dye extravasation produced by a subsequent period of vagal stimulation for up to 4 h.

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