LIPOPROTEIN-LIPASE ACTIVITY IN RAT CARDIOMYOCYTES IS STIMULATED BY INSULIN AND DEXAMETHASONE

Lipoprotein lipase (LPL) activity was studied in rat cardiomyocytes af ter overnight culture (16 h) in the presence of insulin (100 nM) and/o r dexamethasone (100 nM). Insulin in combination with dexamethasone (I NS/DEX) increased heparin-releasable LPL activity by 71 % over the con trol level (566+/-85 versus 331+/-48 nmol/h . mg cell protein). This w as accompanied by a 61 % increase in total cellular LPL activity (914/-89 versus 567+/-64 nmol/h . mg cell protein). The increase in LPL ac tivity occurred at sub-nanomolar concentrations of the hormones, but n either hormone was effective alone. LPL protein mass, quantified by EL ISA, was the same in both control and INS/DEX-treated cells (27.7 vers us 28.6 ng/mg cell protein, respectively), thus LPL specific activity in cardiomyocytes was increased by INS/DEX treatment (0.113 versus 0.0 69 mU/ng LPL protein). These findings emphasize the importance of horm onal interactions in the regulation of LPL in heart tissue.