The origin of plasma arachidonic acid in dogs

Abstract

Total hepatectomy and abdominal evisceration were performed in two groups of dogs to determine if the liver is the only source of plasma arachidonic acid. Venous blood was drawn prior to surgery and hourly for 5–6 hours. Plasma lipids were fractionated by column chromatography into unesterified fatty acids, phospholipids, cholesterol esters, and triglycerides. The per cent composition of the individual fatty acids of these fractions and total esterified fatty acids were determined by gas-liquid chromatography. Hepatectomy resulted in progressive fall of the per cent composition of arachidonic acid of the unesterified fatty acid fraction only. There was no significant depression of any other fatty acid in this fraction, nor was there a change in any fatty acid including arachidonic acid in the phospholipid, cholesterol ester, and triglyceride fractions. Palmitoleic acid was significantly elevated in the unesterfied fatty acid fraction. Similar results were observed in the eviscerated group. There was no change of any fatty acid in the various lipid fractions of a group of sham operated dogs. Lipolysis of adipose tissue triglyceride supplies all fatty acids of the plasma unesterified fatty acid fraction except arachidonic acid which is virtually absent from this tissue. Thus, as the unesterified fatty acids were utilized by the peripheral tissues, all fatty acids except arachidonic acid were replenished by lipolysis of adipose tissue triglyceride. Since the liver was absent in both groups of animals, it was concluded that the liver is the source of plasma arachidonic acid in the fasting dog.