HEPATOMESENTERIC RELEASE AND REMOVAL OF NOREPINEPHRINE IN SWINE

Release and removal of norepinephrine (NE) by hepatomesenteric organs in anesthetized swine were examined using measurements of NE in arteri al, portal, and hepatic venous plasma. NE spillover from the liver and mesenteric organs increased during splanchnic nerve stimulation, vali dating these measurements as indexes of sympathetic outflow. Administr ation of the neuronal uptake-blocking drug desipramine reduced mesente ric NE extraction more than hepatic extraction, suggesting that neuron al uptake was more important for NE removal in mesenteric organs than in the liver. Circulating NE was removed by the liver more efficiently than by mesenteric organs, whereas mesenteric NE spillover (2.46 nmol /min) exceeded liver NE spillover (0.74 nmol/min). Hepatomesenteric NE spillover represented 53% of total body spillover; NE clearance was 4 2% of total body clearance. Because of efficient hepatic extraction of NE released by mesenteric organs, the sum of mesenteric and hepatic N E spillovers (3.20 nmol/min) exceeded net hepatomesenteric spillover e stimated using arterial and hepatic venous measurements alone (1.96 pm ol/min). Thus valid assessment of the substantial amounts of NE releas ed by hepatomesenteric organs requires separate examination of mesente ric and hepatic spillovers.