Insulin stimulates lipoprotein lipase activity and synthesis in adipocytes from septic rats

Gram-negative sepsis suppresses lipoprotein lipase (LPL) activity in adipose tissue which contributes, in part, to the altered clearance of triglycerides. The suppression in LPL activity occurs when plasma insulin concentrations are elevated and insulin-stimulated glucose utilization is impaired. This study was planned to evaluate whether the presence of insulin resistance was responsible for the decrease in adipose LPL activity. Adipocytes were isolated from epididymal fat pads 24 h after inducing sepsis in male Lewis rats by intravenous injection of 4 x 10⁸ colonies of live Escherichia coli/100 g body wt. The decrease in heparin-releasable (HR) LPL activity in adipocytes from the septic rats was evident at the time of isolation and maintained in a 20-h culture. After overnight incubation with insulin (10^-8 M), HR LPL activity was stimulated to a greater extent in adipocytes from septic rats (298%) than in adipocytes from control rats (88%). The insulin stimulation of LPL activity during sepsis could not be attributed to insulin-like growth factor-I (IGF-I) as adipocytes from septic rats appeared to be IGF-I resistant. Insulin-treatment (10^-8 M) increased LPL synthesis 99% in adipocytes from control rats and 136% in adipocytes from septic rats. Insulin treatment also led to a 65 and 62% increase in LPL mass in adipocytes from control and septic rats, respectively. These findings indicate that the sepsis-induced decrease in adipose LPL is not due to insulin resistance with respect to LPL. The insulin stimulation of LPL activity in adipocytes from septic rats appears to be mediated by an increase in LPL synthesis.