Regulation of adipose tissue lipoprotein lipase in young and old rats

Abstract

OBJECTIVE: Changes in tissue lipoprotein lipase have been reported in several of the metabolic disorders commonly associated with ageing, like insulin resistance, obesity and impaired hormonal balance. We have investigated the effect of normal ageing on the nutritional regulation of lipoprotein lipase (LPL) in rat tissues. MEASUREMENTS: In the first experiment, LPL activity and immunoreactive mass were measured in epididymal and perirenal adipose tissue, and soleus and heart muscle tissue. In the following experiments we focused on epididymal adipose tissue. RESULTS: In young rats (aged 29 d, 87±5 g), fasting for 24 h decreased LPL activity in epididymal and perirenal adipose tissue to 31% and 51% of fed control, respectively, while LPL mass increased to 146% and 261%, respectively. Consequently, LPL specific activity (activity/mass ratio) decreased to 20% of control. Other tissues studied did not show any large changes in LPL specific activity with the nutritional state. This suggests that the mechanism responsible for the down-regulation of LPL specific activity is specific for adipose tissue. The down-regulation was gradually blunted with increasing age and was non-existent in the old rats (aged 265 d, 564±14 g). LPL in soleus muscle from young rats was regulated by another mechanism, and was associated with a large increase in LPL activity and mass during fasting (297% and 458% of fed control). Also, this mechanism did not exist in soleus muscle from old rats. Prolonging the fasting period of the old rats to 96 h did not induce the changes in adipose tissue or soleus muscle LPL seen in the young rats. CONCLUSION: The results indicate that the nutritional regulation of LPL in adipose tissue and soleus muscle changes during normal ageing.