Changes in lipoprotein lipase activities in adipose tissue, heart and skeletal muscle during continuous or...

Lipoprotein lipase (LPL) activities in parametrial and interscapular adipose tissue, soleus and adductor longus muscles and hearts of female rats were measured during progressive starvation, chow re-feeding after 24 h starvation and throughout dark and light phases in rats permitted unrestricted access to chow. Adipose-tissue LPL activities declined by 50% after 6 h starvation and continued to fall as the starvation period was extended to 24 h. Skeletal-muscle LPL activities dramatically increased between 9 and 12 h of starvation. Cardiac LPL activities increased 2.5-fold within 6 h of starvation, reaching a maximum after 12 h of starvation. Adipose-tissue LPL activities increased rapidly within 2 h of re-feeding chow ad libitum after 24 h starvation, achieving 'fed ad libitum' values after 6 h. Oxidative-skeletal-muscle LPL activities also increased after 2 h of refeeding and exceeded 'fed ad libitum' values throughout the 6 h re-feeding period. Cardiac LPL activities remained up-regulated for the 6 h of re-feeding. Adipose-tissue LPL activities exceeded those of cardiac or skeletal muscle throughout both light and dark phases. The lowest adipose-tissue LPL activities were observed at 9 h into the light phase. In contrast, cardiac LPL activity declined throughout the dark phase, with a minimum at 9 h into the dark phase. No such variation was observed for skeletal-muscle LPL activities. A diurnal nadir in plasma triacylglycerol (TG) concentrations coincided with the peak in cardiac LPL activities. The results demonstrate that, during unrestricted feeding and re-feeding after prolonged starvation, changes in skeletal-muscle and adipose-tissue LPL activities are neither reciprocal nor co-ordinate. Regulation of cardiac LPL activity during the diurnal cycle may be an important aspect of both of cardiac fuel selection and whole-body TG metabolism.