In vivo regulation of adipose tissue lipoprotein lipase in normal rats made hyperinsulinemic and in hyperinsulinemic genetically-obese (fa/fa) rats.

The objective of this study was to investigate in vivo the effects of various durations of hyperinsulinemia on inguinal white adipose tissue lipoprotein lipase (LPL). Adult genetically-obese (fa/fa) rats were used as a model of chronic hyperinsulinemia. Normal rats infused with insulin as well as with glucose to maintain euglycemia for four days were used as a model of short-term hyperinsulinemia. Normal rats studied during a euglycemic-hyperinsulinemic clamp were used as a model of acute effects of hyperinsulinemia. The levels of LPL mRNA, LPL protein and LPL total activity in inguinal white adipose tissue were measured. In both chronic and long-term hyperinsulinemia, a marked increase in total LPL activity was observed which was associated with an increase in tissue LPL protein abundance. After five hours of hyperinsulinemia, as achieved during the clamps, only total LPL activity was increased. An increase in LPL mRNA was measured only in adipose tissue of obese rats. The differences observed in the regulation of LPL mRNA between insulin-treated rats and genetically-obese animals may be explained either by the large increase in adipose tissue glucose metabolism of insulin-treated rats compared to obese rats and/or by other factors that may be present in genetically-obese (fa/fa) rats.