ROLE OF INSULIN-RESISTANCE IN DECREASING LIPOPROTEIN-LIPASE ACTIVITY IN TUMOR-BEARING RATS

The role of insulin resistance in the tumor-induced decrease in tissue lipoprotein lipase (LPL) activity was studied in vivo and vitro in me thylcholanthrene-induced sarcoma-bearing rats. Intraperitoneal (ip) in jection of 2 U of regular insulin resulted in high-adipose LPL activit y in control rats (CTR) of 122.0 +/- 42.4 U/mg tissue, but it had litt le effect on tumor-bearing rats (TBR), which showed a value of only 9. 6 +/- 5.5 U/mg tissue (P = 0.002), When adjusted for serum insulin con centrations, adipose LPL activity remained significantly different bet ween the TBR and CTR at 0.19 +/- 0.17 and 0.78 +/- 0.29 U/mg tissue, r espectively (P = 0.02), Following the in vitro incubation with either 1.44 g/l glucose of 1 x 10(-8) U insulin of adipose tissue fragments o btained from the TBR and the CTR, measurable LPL activity was maintain ed in the tissue from the CTR for 2 h but not in that from the TBR, Th ese results suggest that the decreased LPL activities seen in the tumo r-bearing state may be mediated by insulin resistance.