In vitro addition of epinephrine, norepinephrine, and carnitine alters palmitate oxidation and esterification in isolated ovine hepatocytes

Abstract

Hepatocytes from 4 wethers were used to study the effects of carnitine and increasing concentrations of epinephrine and norepinephrine on palmitate oxidation and esterification. Liver cells were isolated from the wethers and incubated in Krebs-Ringer bicarbonate buffer with 1 mM [¹⁴C]-palmitate. Radiolabel incorporation was measured in CO₂, acid-soluble products, and esterified products, including triglyceride, diglyceride, and cholesterol esters. Carnitine increased production of CO₂ and acid-soluble products from palmitate by 41% and 216%, respectively, but had no effect on conversion of palmitate to esterified products. Epinephrine had a quadratic-increasing effect on palmitate oxidation to CO₂, but norepinephrine did not increase palmitate oxidation to CO₂. Neither epinephrine nor norepinephrine affected the production of acid-soluble products from palmitate. Increasing concentrations of norepinephrine and epinephrine linearly increased rates of triglyceride formation from palmitate. Increasing norepinephrine concentrations linearly increased diglyceride and cholesterol ester formation from palmitate in the presence of carnitine; epinephrine did not affect diglyceride or cholesterol ester formation. In general, catecholamine treatment had the greatest effect on the formation of esterified products from palmitate, and effects of norepinephrine were more pronounced than epinephrine. Conditions that result in catecholamine release might lead to fat accumulation in the liver.

Keywords: catecholamine; fatty acid; hepatocytes; metabolism.