LIPOPROTEIN-LIPASE AND HORMONE-SENSITIVE LIPASE ACTIVITY AND MESSENGER-RNA IN RAT ADIPOSE-TISSUE DURING PREGNANCY

To investigate the factors controlling maternal depot fat accumulation during early pregnancy and net decrease during late pregnancy, the ac tivity and mRNA expression of adipose tissue lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) were related to several other lipid metabolic parameters. Virgin control rats, pregnant rats (at days 12, 15, 19, and 21), and lactating rats (at days 5 and 10 postpartum) wer e studied. In adipose lumbar tissue of late pregnant rats, LPL activit y decreased to about one-third that of the virgin control animals, wit h < 10% of initial LPL mRNA expressed as determined by Northern blots. HSL activity increased maximally 1.5-fold with a fourfold increase of HSL expression at days 12-15 of pregnancy and decreased to control le vels after parturition. The HSL-to-LPL mRNA and activity ratios were e nhanced from days 15 and 19 of pregnancy, respectively, and remained s o even during lactation, mainly because of the marked lowering of the LPL values. This enhancement coincided with increments in plasma free fatty acids and glycerol levels indicating an increased depot fat brea kdown. These results give no indication of an involvement of LPL and H SL gene expression changes in the accumulation of maternal depot durin g early pregnancy. In contrast, such changes could be responsible for the net breakdown of this fat depot during late gestation. Thus, durin g this physiological state, long-term (e.g., transcriptional) regulati on of LPL and HSL gene expression could be an important mechanism for the control of adipose tissue mass breakdown during late gestation.