Effects of dietary triolein and sunflower oil on insulin release and lipid metabolism in zucker rats

Obese and lean male Zucker rats were fed ad libitum on diets containing either 50 (L) or 200 (H) g/kg diet of either triolein (T) or sunflowerseed oil (S). The specific activity of the hepatic microsomal Δ9 desaturase enzyme was depressed in both lean and obese rats fed the HS diet compared with the other three diets. The fatty acid composition of liver and subcutaneous white adipose tissue lipids were consistent with a lower Δ9 desaturation activity in rats fed the H diets, particularly for the HS diet. In both genotypes, microsomal Δ9 desaturase activity and the ratio of 16∶1/(16∶0+16∶1) fatty acids in liver lipids were inversely related to the proportion of 18∶2 in liver lipid. Plasma insulin concentrations and rates of glucose-stimulated insulin release in vivo were higher in obese rats compared with lean rats, and plasma insulin levels were higher in rats fed S compared with T. There was no relationship between Δ9 desaturase activity and either plasma insulin concentration or rates of insulin release in vitro. These findings suggest that hepatic Δ9 desaturase activity of Zucker rats is responsive to changes in the proportion of 18∶2 in liver lipids but is not affected by changes in insulin secretion.