DIURNAL RHYTHMS AND EFFECTS OF FASTING AND REFEEDING ON RAT ADIPOSE-TISSUE LIPOPROTEIN-LIPASE

The activity of lipoprotein lipase (LPL) in adipose tissue is modulate d by changes in the nutritional status. We have measured LPL activity, mass, and mRNA levels in rat adipose tissue during normal feeding cyc les, during short- and long-term fasting, and during refeeding after f asting. LPL activity displayed a diurnal rhythm. The activity was high est during the night and early morning, decreased to a minimum during the early afternoon, and then increased again. These changes correspon ded to the feeding pattern. The increases and/or decreases resulted fr om changes in LPL synthetic rate compounded by posttranslational mecha nisms. During shortterm fasting, LPL specific activity decreased to <3 0% of control. The specific activity was restored within 4 h by refeed ing. On longer fasting, LPL mRNA decreased. This became significant fr om 36 h. On refeeding, it took 12 h to restore the mRNA levels, wherea s 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 upregulati on after refeeding. On longer fasting, other mechanisms affecting LPL transcription and synthesis come into play, and upregulation after ref eeding is slowed down.