Sympathetic control of Na, K transport in perfused submaxillary main duct of rat

The effect of stimulating the sympathetic innervation to rat submaxillary gland on ductal transport of Na, K, and water and on transepithelial PD was tested in the main excretory duct during perfusion through its lumen. Stimulation of the sympathetic nerve, supramaximally, caused a decrease of 30-40% in net flux of Na from, and of K to, the lumen in ducts perfused with medium containing Na and K in isotonic concentrations. Net flux of water was unaffected. Transductal PD decreased by about 30% during supramaximal stimulation. Changes in PD and net cation fluxes were reversible. These effects of supramaximal stimulation of the sympathetics on ductal transport resemble those reported to occur after large doses of isoproterenol and suggest an adrenergic secretomotor innervation to the ducts. However, changes in PD evoked by supramaximal stimulation of the sympathetic nerve could not be suppressed with propranolol, but were with phenoxybenzamine, indicating that alpha-adrenergic receptors are primarily involved in mediating at least the electrical responses of duct cells to sympathetic nerve stimulation.