Studies on serum lipids, insulin, and glucagon and on muscle triglyceride in rats adapted to high-fat and high-carbohydrate diets

A comparison was made of lipid circulation, storage, and mobilization in rats adapted to lard or glucose diets. In the morning, lard-fed rats had higher blood triglyceride (TG) and free fatty acid (FFA) levels. In the evening TG was higher, but FFA was significantly lower in the lard vs. the glucose group. Fasting did not produce the characteristic increase in blood FFA in the lard-fed rats but was associated with a severe drop in their serum TG. Circulating glucose and insulin were not affected, while glucagon levels were increased by lard feeding. Nicotinic acid decreased fasting FFA levels to a greater extent in the glucose-fed rats. It was concluded that lard feeding depresses mobilization of fat from adipose tissue; on the other hand, it was found to increase storage and utilization of muscle TG. Fat feeding increased diaphragm TG concentrations threefold, as well as the number and size of intracellular fat droplets at the light and electron microscopic levels. Fasting decreased diaphragm TG in both groups, but the amount lost was greater in the fat-fed rats. Also, in vitro basal isoproterenol-stimulated (1 μg/ml) FFA release by the incubated diaphragm was higher in the lard-fed group.