Splanchnic Cortisol Production in Dogs Occurs Primarily in the Liver

Abstract

Eight dogs underwent combined hepatic/portal vein catheterization and infusion of D4-cortisol in order to determine the relative contributions of the viscera and liver to splanchnic cortisol production. D4-cortisol concentrations progressively decreased from 2.6 ± 0.1 to 2.4 ± 0.1 to 1.7 ± 0.1 μg/dl (P < 0.001 by ANOVA) from hepatic artery to portal vein to hepatic vein, respectively, indicating 8 ± 3 and 28 ± 3% extraction across the viscera and liver, respectively. On the other hand, hepatic artery, portal vein, and hepatic vein cortisol concentrations did not differ (0.31 ± 0.12 vs. 0.28 ± 0.11 vs. 0.27 ± 0.10 μg/dl, respectively), indicating zero net cortisol balance. This meant that 1.0 ± 0.1 μg/min of cortisol was produced within the splanchnic bed, all of which occurred within the liver (1.2 ± 0.1 μg/min). On the other hand, visceral cortisol production did not differ from zero (−0.2 ± 0.2 μg/min; P < 0.001 vs. liver). Flux through the 11β hydroxysteroid dehydrogenase (HSD) type 1 pathway can be measured by determining the rate of conversion of D4-cortisol to D3-cortisol. D3-cortisol concentrations were lower in the portal vein than hepatic artery (0.45 ± 0.03 vs. 0.48 ± 0.02, respectively; P < 0.01) but did not differ in the portal vein and hepatic vein, indicating net uptake across the viscera but zero balance across the liver. D3-cortisol production with the viscera and liver averaged 0.2 ± 0.1 μg/min (P = NS vs. zero production) and 0.6 ± 0.1 μg/min (P < 0.001 vs. zero production; P < 0.001 vs. viscera production), respectively. We conclude that most, if not all, of splanchnic cortisol production occurs within the liver. Taken together, these data suggest that the high local cortisol concentrations generated via the 11β HSD type 1 pathway within the liver likely contribute to the regulation of hepatic glucose, fat, and protein metabolism.