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Features of syndrome X develop in transgenic rats expressing a non-insulin responsive phosphoenolpyruvate
A W Thorburn1, M E Baldwin, G Rosella
1Department of Medicine, University of Melbourne, Royal Melbourne Hospital, Parkville, Victoria, Australia.
Aims/Hypothesis:
Obesity, glucose intolerance, dyslipidaemia and hypertension are a cluster of disorders (syndrome X) affecting many people. It has been hypothesised that these abnormalities are caused by insulin resistance, but definitive proof is lacking. We have developed transgenic rats in which the rate-limiting gluconeogenic enzyme, phosphoenolpyruvate carboxykinase, is non-insulin responsive. The aim of our study was to investigate whether syndrome X develops in these animals and if a high-fat diet interacts with this genetic defect.
Methods:
Chow-fed transgenic and control rats aged 1, 3, 6 and 17 months and a subgroup of transgenic and control rats fed chow plus cafeteria foods for 6 months were examined for features of syndrome X.
Results:
At 3 months, transgenic rats had fasting and postprandial hyperinsulinaemia, mild obesity (in abdominal and, to a lesser extent, peripheral regions) and fasting hypercholesterolaemia. Hypertriglyceridaemia was evident after 6 months while hyperglycaemia was apparent at 17 months. Hypertension had not developed by 17 months. The effect of a high-fat diet on insulin, glucose, body weight and body fat was more dramatic than the effect of the transgene alone while the effect of a high-fat diet on cholesterol and triglyceride was similar to the transgene. This illustrates that a high-fat diet is a potent catalyst for many abnormalities associated with syndrome X. There was no evidence of an additive effect of the high-fat diet plus transgene.
Conclusion/Interpretation:
Therefore rats genetically-engineered with a non-insulin responsive gluconeogenic enzyme develop several aspects of syndrome X, supporting the hypothesis that insulin resistance initiates this cluster of disorders.