Pancreatic vasoconstrictor responses are regulated by neurons in the rostral ventrolateral medulla

The pancreas receives sympathetic input which arises from several premotor cell groups in the CNS including the rostral ventrolateral medulla (RVLM). In this study, we examined the influence of electrical stimulation of the RVLM on pancreatic blood flow measured by laser Doppler flowmetry and gastric blood flow measured by ultrasonic Doppler flowmetry in halothane-anesthetized rats. The laser Doppler flow measurement technique was validated by demonstration that pancreatic conductance was reduced by systemic administration of the vasoconstrictor phenylephrine and increased by the vasodilator sodium nitroprusside. Sympathetic vasomotor withdrawal induced by either administration of phenylbiguanide (2 and 10 μg/kg, i.v.) or electrical stimulation of the central end of the cervical vagal trunk (5 Hz, 2 ms, 50-150 μA) produced depressor responses and increases in pancreatic and gastric vascular conductance. Electrical stimulation of the RVLM (50 Hz, 0.5 ms, 25-75 μA) produced pressor and tachycardic responses accompanied by decreases in pancreatic and gastric vascular conductance. All responses to RVLM stimulation were abolished by blockade of ganglionic neurotransmission (hexamethonium bromide, 20 mg/kg, i.v.). These data suggest that RVLM presympathetic vasomotor neurons are a primary source of tonic sympathetic vasomotor drive to the pancreatic and gastric vasculature.