Lipogenesis from carbohydrate in male and female rats

Abstract

Epidemiological surveys have shown that premenopausal women are less susceptible to atherosclerosis than men. There is also a positive correlation between the levels of serum triglyceride and the incidence of atherosclerosis. In this study the rat has been used as an experimental model to examine the effects of the prolonged ingestion of 5% sucrose and 5% glucose solutions, in addition to the normal diet. In general, both male and female animals on the sucrose diet showed the greatest increases in body weight and also in the weights of liver, small intestine, heart, kidney and adipose tissue. Male rats had significantly higher levels of serum triglycerides than females and the sucrose diet increased the levels of serum triglyceride to a greater extent than the glucose diet in both sexes. No significant differences in serum phospholipid were observed but, in most cases, serum cholesterol levels were higher in females than in males. The levels of all three lipids in the heart and liver were generally higher in females than in males, but the effect of various diets on these factors were minimal. A study on the effect of the diets on various carbohydrate metabolites demonstrated that hepatic a-glycerophosphate, dihydroxyacetone phosphate and fructose 1,6-diphosphate levels were lower in females than in males. There was, however, no significant sex difference in the level of hepatic fructose 1-phosphate. No dramatic sex differences in these metabolites, were found in heart and kidney. Following the short terra gastric intubation of 70% fructose no sex differences in fructose 1-phosphate levels were observed either in the liver or in the small intestine. Isolated hepatocytes, which responded to physiological levels of glucagon with regard to lipogenesis from glucose and to gluconeogenesis from lactate, were prepared. No sex differences in the capacity of hepatocytes to synthesize either total lipid or triglyceride, from fructose, glycerol or glucose, were observed. However, the incubation of hepatocytes with glycerol raised the a-glycerophosphate levels to a greater extent in the male than in the female. In all cases, hepatocytes synthesized lipids at a faster rate from glycerol than from fructose. Glucose was incorporated into lipid at a slower rate than either of the other substrates.