Effect of chronic hyperinsulinism on metabolic parameters and histopathology in rats fed sucrose or starch

The purpose of this study was to determine the effects of chronic hyperinsulinism on metabolic risk factors and on the histopathologic changes in the heart and aorta of rats fed sucrose or starch diets for 8 months. Hyperinsulinism was attained by the subcutaneous implantation of osmotically driven minipumps partially coated with paraffin so as to deliver 3 units/day of porcine insulin for up to 4 weeks. Control rats were implanted with pumps containing 1.6% glycerol. There were initially 12 rats each in four groups of rats; sucrose-insulin, sucrose-control, starch-insulin, starch-control. Nonfasted blood insulin levels obtained every 3 weeks from the tail vein averaged 553, 156, 426, and 107 microU/ml in sucrose-insulin, sucrose-control, starch-insulin, and starch-control rats, respectively. Sucrose-fed rats had greater body weight, deposited more body fat, and had higher levels of nonfasting insulin and glucose and 6-hour fasted triglyceride than did starch-fed rats. Rats receiving insulin had greater body weight and removable fat weight, higher levels of nonfasting and fasting insulin and lower level of nonfasting glucose than did rats not receiving insulin. Neither hyperinsulinism nor the type of dietary carbohydrate significantly affected the amount of blood cholesterol. Histopathology of the heart and aorta revealed no unique changes above those commonly observed in laboratory rats as a function of age.