THE REGULATION OF ADIPOSE-TISSUE AND MUSCLE LIPOPROTEIN-LIPASE IN RUNNERS BY DETRAINING

To study the mechanism of lipoprotein lipase (LPL) regulation by exerc ise, we recruited 16 healthy athletes to undergo a 2-wk period of detr aining. Fasting fat and muscle biopsies were performed both before and after the detraining period. In muscle, detraining resulted in a decr ease in LPL activity in both the heparin-releasable (HR) (-45%, P < 0. 05) and cellular (extractable [EXT]) (-75%, P < 0.005) fractions, with no significant changes in LPL immunoreactive mass and mRNA levels. Ho wever, several subjects demonstrated parallel decreases in LPL mass an d mRNA levels with detraining, suggesting that there is some degree of heterogeneity in response. In adipose tissue, detraining had the oppo site effects on LPL activity. In the HR fraction, detraining resulted in an 86% increase (P < 0.005) in LPL activity, which was paralleled b y a 100% (P = 0.02) increase in HR mass. However, there was no signifi cant change in EXT LPL activity or EXT LPL mass. There were no changes in adipose LPL synthetic rate or LPL mRNA levels with detraining. The ratio of adipose tissue / muscle LPL, which may be an important indic ator of the tendency for storage of circulating lipids in adipose tiss ue, increased significantly after detraining. The adipose / muscle LPL ratio was 0.51+/-0.17 in the exercising runners, and 4.45+/-2.46 in t he same runners after detraining (P < 0.05). Thus, detraining of athle tes resulted in a decrease in muscle LPL that occurred through posttra nslational mechanisms, whereas adipose tissue LPL increased, also due to posttranslational changes. This decrease in muscle LPL, coupled wit h an increase in adipose LPL, yielded a condition favoring adipose tis sue storage.