The vasodilator and secretory effects elicited by sympathetic nerve stimulation in cat submandibular gland

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The effects of electrical stimulation of the peripheral cut ends of the ascending cervical sympathetic trunk on vasomotor, particularly vasodilator, response were studied in relation to salivary secretion in the cat submandibular gland. The vasodilator and salivary responses were compared by stimulating the peripheral cut ends of the sympathetic nerve at various intensities (1–8 V), durations (5–60 s) and frequencies (1–100 Hz) using a 2 ms pulse duration. Electrical stimulation of the cervical sympathetic nerves caused vasoconstriction followed by vasodilatation and salivation. There were certain differences in the maximal responses of vasodilatation and salivation during sympathetic stimulation. For example, optimal frequencies for vasodilatation and salivation were 10 Hz and 20 Hz, respectively. Time-dependent increases in vasodilatation and salivary secretion were seen for periods of up to 30 s and 60 s, respectively. The volume of salivation was not necessarily correlated with the magnitude of vasodilator response. Prior treatment with an α-adrenoceptor blocking agent phentolamine largely reduced vasoconstriction ( P < 0.01) and almost completely abolished salivary secretion ( P < 0.01), but had only a slight inhibitory effect on vasodilatation (0.1 < P < 0.05). Propranolol (a β-adrenoceptor blocking agent) pretreatment significantly decreased vasodilatation ( P < 0.05) but had no statistically significant effect on vasoconstriction or salivation. Scopolamine (a muscarinic cholinoceptor blocking agent) had no effect on the responses followed by sympathetic nerve stimulation but abolished the vagal mediated reflex salivation, indicating that the salivation, but not vasodilatation, elicited by activation of the afferent fibers of the vagus nerve is mediated via parasympathetic muscarinic fibers. The present results indicate that α-adrenoceptors participate exclusively in salivary and vasoconstrictor responses, whereas β-adrenoceptors are in part involved in sympathetic-induced vasodilatation in the cat submandibular gland.