Hepatic and gut clearance of catecholamines in the conscious dog

Our aim was to assess hepatic and gut catecholamine clearance under normal and simulated stress conditions. Following a 90-minute saline infusion period, epinephrine ([EPI] 180 ng/kg x min) and norepinephrine ([NE] 500 ng/kg x min) were infused peripherally for 90 minutes into five 18-hour fasted, conscious dogs undergoing a pancreatic clamp (somatostatin plus basal insulin and glucagon). Arterial plasma levels of EPI and NE increased from 44 +/- 9 to 2,961 +/- 445 and 96 +/- 6 to 6,467 +/- 571 pg/mL, respectively (both P < .05). Portal vein plasma levels of EPI and NE increased from 23 +/- 8 to 1,311 +/- 173 and 79 +/- 10 to 3,477 +/- 380 pg/mL, respectively (both P < .05). Hepatic vein plasma levels of EPI and NE increased from 5 +/- 2 to 117 +/- 33 and 48 +/- 10 to 448 +/- 59 pg/mL, respectively (both P < .05). Net hepatic and gut EPI uptake increased from 0.5 +/- 0.1 to 30.0 +/- 3.0 and 0.4 +/- 0.1 to 26.3 +/- 4.0 ng/kg x min, respectively (both P < .05). Net hepatic and gut NE uptake increased from 1.5 +/- 0.4 to 74.7 +/- 8.4 and 0.8 +/- 0.2 to 57.9 +/- 7.6 ng/kg x min, respectively (both P < .05). Neither the net hepatic (0.86 +/- 0.05 to 0.93 +/- 0.02) nor gut (0.45 +/- 0.10 to 0.55 +/- 0.04) fractional extraction of EPI changed significantly during the simulated stress condition. Net hepatic and gut spillover of NE increased from 0.8 +/- 0.2 to 3.5 +/- 1.3 and 0.6 +/- 0.2 to 8.8 +/- 2.0 ng/kg x min, respectively, during catecholamine infusion (both P < .05). These results indicate that (1) approximately 30% of circulating catecholamines are cleared by the splanchnic bed (16% and 14% by the liver and gut, respectively); (2) the liver and gut remove a large proportion (approximately 86% to 93% and 45% to 55%, respectively) of the catecholamines delivered to them on first pass; and (3) high levels of plasma catecholamines increase NE spillover from both the liver and gut, suggesting that the percentage of NE released from the presynaptic neuron that escapes the synaptic cleft is increased in the presence of high circulating catecholamine levels.