Long-Term Fructose versus Corn Starch Feeding in the Spontaneously Hypertensive Rat

1. Fructose feeding, as opposed to vegetable starch feeding, has been shown to elevate blood pressure and to decrease insulin sensitivity in normotensive rats. The long-term relevance of this is unclear, and data in hypertensive strains are scarce. 2. We studied the effects of 27 weeks of a fructose-versus a corn-starch-enriched (69.5% w/w) diet in the spontaneously hypertensive rat. 3. In both dietary groups, blood pressure increased with ageing, with no apparent difference between the diets. The fructose-fed rats gained less weight. However, even selecting fructose-fed rats that matched the weight gain in the corn starch group, did not reveal a significant elevation of systolic blood pressure over time. 4. Extracellular fluid volume was comparable in fructose-fed and corn-starch-fed rats. No effects on creatinine clearance, proteinuria or renal histology were found. Fasting values of plasma triacylgycerols and cholesterol were increased mildly after 2 weeks on the fructose diet. However, fasting glucose and insulin measured after 2 weeks, and the response to an intraperitoneal glucose load, were no different. After 23 weeks of the diets, fasting values of plasma glucose, insulin, triacylglycerols and cholesterol did not differ. There were small differences in the response of plasma glucose levels to the intraperitoneal glucose load, but the area under the curve was not different. The baseline insulin resistance present in spontaneously hypertensive rats possibly blunts the metabolic response to dietary fructose. 5. After 27 weeks, the diets were switched in crossover design, and measurements were continued until 39 weeks. The fructose diet did not elevate systolic blood pressure in this follow-up experiment. 6. To summarize, long-term fructose versus corn starch feeding did not increase systolic blood pressure in spontaneously hypertensive rats. Metabolic variables were transiently affected and renal function was undisturbed. These findings suggest that long-term fructose feeding, compared with other dietary carbohydrates, is not specifically harmful in the spontaneously hypertensive rat.