Post Heparin Lipolytic Activity in Aged Rat

Abstract

We investigated the changes in triglyceride metabolism induced by various lipid loading in aged and young rats in order to elucidate the mechanism of hyperlipidemia in the aged. 24 month-old rats were used as the aged and were compared with 2 month-old rats. Serum triglyceride in the aged rats were higher than those of the young rats. After oral oil loading, serum triglyceride was increased more accurately in aged rats than in young rats. There are three possible mechanisms by which serum triglyceride was increased.
(1) Increase in triglyceride absorption from intestine. (2) Increase in triglyceride synthesis in liver. (3) Decrease in triglyceride clearance from serum. As to the possibility of (1), it may be excluded because decrease in triglyceride absorption from intestine according to aging was reported. As to the possibility of (2), activities of Acetyl-CoA carboxylase, Acyl-CoA synthetase and Triglyceride Synthesis were measured in the liver of the aged or the young rats. These three activities were not different in the aged and the young rats. As to the possibility of (3), decrease in triglyceride clearance from serum was observed in the aged rats after intravenous administration of lipid. One of the most important factors which regulate triglyceride clearance from serum is lipoprotein lipase activity in vascular wall. We discussed the capacity of this enzymatical activity by measuring post heparin lipolytic activity (PHLA) and heparin releasable lipoprotein lipase activity in epididymal adipose tissue in the aged or the young rats. The both activities were decreased in the aged rats compared with the young rats. Above results suggest that hypertriglyceridemia in the aged might depend on the decrease in the capacity or adaptability of lipoprotein lipase activity to postprandial increase in serum lipid.