Diurnal rhythms and effects of fasting and refeeding on rat adipose tissue lipoprotein lipase.

The activity of lipoprotein lipase (LPL) in adipose tissue is modulated by changes in the nutritional status. We have measured LPL activity, mass, and mRNA levels in rat adipose tissue during normal feeding cycles, during short- and long-term fasting, and during refeeding after fasting. LPL activity displayed a diurnal rhythm. The activity was highest during the night and early morning, decreased to a minimum during the early afternoon, and then increased again. These changes corresponded to the feeding pattern. The increases and/or decreases resulted from changes in LPL synthetic rate compounded by posttranslational mechanisms. During short-term fasting, LPL specific activity decreased to < 30% of control. The specific activity was restored within 4 h by refeeding. On longer fasting, LPL mRNA decreased. This became significant from 36 h. On refeeding, it took 12 h to restore the mRNA levels, whereas tissue LPL activity and mass could not be fully restored by 36 h of refeeding. These data show that LPL activity during short-term fasting is regulated posttranscriptionally, which allows for quick upregulation after refeeding. On longer fasting, other mechanisms affecting LPL transcription and synthesis come into play, and upregulation after refeeding is slowed down.