Extraction of epinephrine and norepinephrine by the dog pancreas in vivo

Abstract

This study determined the fractional extraction of epinephrine and norepinephrine by the in situ dog pancreas. Plasma samples for epinephrine measurements were taken simultaneously from the femoral artery and the superior pancreaticoduodenal vein. Pancreatic extraction of epinephrine was 73 +/- 5% when basal arterial epinephrine levels were 380 +/- 93 pg/mL, 76 +/- 4% when arterial levels were 896 +/- 123 pg/mL (epinephrine infused intravenously at 20 ng/kg/min), and 84 +/- 1% when arterial levels were 2,956 +/- 414 pg/mL (epinephrine infused intravenously at 80 ng/kg/min) suggesting that the process of epinephrine extraction by the pancreas is not saturable over this range. During a similar sampling protocol, norepinephrine was infused intravenously at 4 micrograms/kg/min; pancreatic extraction of norepinephrine was then 65 +/- 7% when arterial norepinephrine levels were 107,000 +/- 28,000 pg/mL. In separate experiments, lower rates of norepinephrine (12 to 1,200 ng/min) were infused directly into the pancreatic artery and pancreatic norepinephrine extraction was calculated; it ranged between 66% and 75%. Because the pancreas produces as well as extracts norepinephrine, a third technique was required to determine pancreatic norepinephrine extraction at the lower endogenous levels of norepinephrine; 3H-norepinephrine was infused intravenously and the arteriovenous difference of 3H-norepinephrine was measured. Fractional extraction of 3H-norepinephrine was 74 +/- 4% both in the basal state (arterial norepinephrine level = 202 +/- 44 pg/mL) and during systemic, glucopenic, stress induced by 2-deoxy-glucose (arterial norepinephrine level = 636 +/- 70 pg/mL). These data suggest that also the norepinephrine extraction process by the pancreas is not saturable.(ABSTRACT TRUNCATED AT 250 WORDS)