Hormonal and lipogenic and gluconeogenic enzymatic responses in LA/N-corpulent rats.

Genetically obese normotensive rats, LA/N-corpulent (cp), were fed ad libitum diets containing either 54% sucrose or cooked corn starch for 12 weeks. Twenty-four rats were used for the study; half were corpulent (cp/cp) and half were lean (cp/+ or +/+). Fasting levels of plasma insulin, glucose, corticosterone, glucagon and growth hormone, and activities of liver and epididymal fat pad glucose-6-phosphate dehydrogenase (G6PD), malic enzyme (ME), and liver and kidney glucose-6-phosphatase (G6Pase), fructose 1,6-diphosphatase (FDPase), and phosphoenolpyruvate carboxykinase (PEPCK) were measured. A significant phenotype effect was observed in insulin, corticosterone, growth hormone, and liver G6PD, ME, FDPase, and kidney PEPCK, G6Pase, FDPase, and epididymal fat pad G6PD and ME (corpulent greater than lean), and glucagon (lean greater than corpulent). Diet effect (sucrose greater than starch) was significant for plasma glucose, liver ME, and kidney G6Pase. Although not significant at the P less than 0.05 level, insulin, corticosterone, liver G6PD and FDPase and kidney FDPase tended to be higher in sucrose-fed rats. This study suggests that the corpulent rat is more lipogenic and gluconeogenic than the lean, and that the hormones responsible are effective in keeping both the lipogenic and gluconeogenic enzyme activity elevated.