Effect of Diet and Insulin on the Morphology and TPNH Generating Enzyme Activities of Rat Adipose Tissue ∗

Abstract

Summary

The activities of TPN malic enzyme and aggregate hexomonophosphate shunt dehydrogenases were determined in epididymal fat pads of rats subjected to the following treatment: (1) ad libitum chow fed; (2) fasted 72 hr; (3) refed sucrose diet 72 hr; (4) refed sucrose diet plus insulin; (5) refed high-fat diet; and (6) refed high-fat diet plus insulin. Refeeding the sucrose diet for 72 hr resulted in more than a six-fold increase in malic enzyme activity, and approximately a doubling of the activity of the shunt enzymes over the prefast levels. Refeeding the high-fat, carbohydrate-free diet resulted in restoration of enzyme activities to prefast levels. Administration of exogenous insulin resulted in no change beyond that produced by the respective diets alone. Fasting resulted in a decrease in nucleolar and cytoplasmic RNA staining and a reduction of the mean cell size. Refeeding sucrose induced a marked enlargement of nucleoli and increased cytoplasmic basophilia with essentially no changes in mean cell size. Refeeding the high-fat diet produced a striking hypertrophy of fat cells, whereas the nucleolar and cytoplasmic RNA staining was comparable to the prefast state. Exogenous insulin did not produce marked differences in either of the two diet groups.

The authors are indebted to Elizabeth Zizzi and Patricia Hopkins for valuable technical assistance.