Glucagon‐like peptide1 and sympathetic vasomotor function

Glucagon‐like peptide 1 (GLP‐1) is a member of the superfamily of glucagon‐related peptides. GLP‐1 increases Fos expression in RVLM presympathetic neurons and adrenal medulla chromaffin cells and it has been proposed that this may account for the pressor and tachycardic effects of systemic GLP‐1 administration. In this study we have tested the hypothesis that systemic GLP‐1 activates RVLM presympathetic neurons and sympathetic vasomotor outflow. In separate groups of halothane‐anesthetized, paralysed male Sprague‐Dawley rats, we recorded the discharges of RVLM presympathetic neurons and splanchnic sympathetic discharge (SSND) along with arterial blood pressure (AP) and heart rate (HR). GLP‐1 (3–300 pmol/kg, i.v.) produced modest increases in AP (5–15 mmHg) and no consistent changes in HR. RVLM presympathetic neurons were identified on the basis of their barosensitivity and axonal projection to the thoracic spinal cord. These neurons were also inhibited by phenylbiguanide (10 μg/kg, i.v.; von Bezold‐Jarisch reflex) and a sub‐population was inhibited by cholecystokinin (4 μg/kg, i.v.). GLP‐1 (3–300 pmol/kg, i.v.) produced only modest increases (10–20%) in the discharge rates of these cells. GLP‐1 had minor and inconsistent effects on SSND. We conclude that GLP‐1 has modest effects on sympathetic vasomotor outflow in anaesthetised rats.