Fasting increases tissue uptake and interconversion of plasma unesterifiedlinoleic acid in guinea pigs

A large part of the arachidonic acid (20:4 n-6) pools in some extrahepatic tissues can be formed by local interconversion of linoleic acid (18:2 n-6) taken up as free fatty acid (FFA) from blood in both rats and guinea pigs. This study investigates the rate of uptake and interconversion of unesterif ied C-14-18:2 by different tissues in fasted guinea pigs. The initial half- life of C-14-18:2 in plasma was 5.8 s. The average concentration of plasma FFA was 551.3 nmol ml(-1) and of plasma FFA-18:2 was 67.3 nmol ml(-1). The total amount of 20:4 formed in the liver was 1.8 +/- 0.3 nmol min(-1), whic h was lower than that in the gastrointestinal tract (3.1 nmol min(-1)), bon e marrow (6.0 nmol min(-1)) and lung (2.1 nmol min(-1)). Due to the fast tu rnover and higher concentration of plasma FFA-18:2 in the fasting state, th e retained 18:2 in tissue lipids was 5.8-25.6-fold higher than that in fed guinea pigs [L. Zhou et al. Biochim. Biophys. Acta 1349 (1997) 197-210]. Th e total delta 6-desaturase products both in liver and in extrahepatic tissu es were also increased, 3.8-fold in liver, 7.2-fold in upper small intestin e, 6.0-fold in colon, and 6.5-fold in bone marrow. The increased rate of ti ssue uptake of FFA during fasting is thus linked to an increased local inte rconversion of plasma FFA-18:2, which is an important source of 20:4 in som e extrahepatic tissue in guinea pigs. (C) 1999 Elsevier Science B.V. All ri ghts reserved.