Decreased sensitivity to the inhibitory effect of insulin on the secretion of very—low-density lipoprotein in cultured hepatocytes from fructose-fed rats

Abstract

Hepatocytes were prepared from rats fed a chow diet (control-fed) and from rats fed a similar diet in which the drinking water contained 10% (wt/vol) fructose (fructose-fed). Both types of hepatocyte preparations were cultured for ≤48 hours in supplemented Waymouth's medium containing increasing concentrations of bovine insulin (0 to 780 nmol/L). During the first 24 hours of culture, hepatocytes from fructose-fed rats secreted more very—low-density lipoprotein (VLDL) triacylglycerol (TAG) than hepatocytes from control-fed rats. This difference persisted at all concentrations of insulin. There was no difference in the rate of secretion of apolipoprotein B (apo B). In both control-fed and fructose-fed animals, the inhibitory effect of insulin on the secretion of VLDL was greater on the second versus the first day of culture. Under these conditions, hepatocytes from fructose-fed groups were less sensitive to insulin inhibition as compared with those from the control-fed group. This was evidenced by the following: (1) the decreased inhibitory effect of insulin on the secretion of both total and newly synthesized VLDL TAG, (2) the attenuated inhibitory effect of insulin on the secretion of VLDL apo B, (3) the decreased potency of insulin in suppressing the secretion of VLDL TAG in TAG-depleted hepatocytes from fructose-fed as compared with control-fed animals, and (4) the larger proportion of newly synthesized TAG secreted as VLDL in hepatocytes from fructose-fed rats as compared with controls. This difference was exacerbated at higher concentrations of insulin. These results suggest that the increased rate of secretion of VLDL from livers of fructose-fed rats is due to (1) an increased basal rate of secretion and (2) a decreased sensitivity to the inhibitory effect of insulin.