Short term effects of fructose on blood glucose dynamics and meal initiation

We have previously shown that small (-11%) transient (approximately 18 min) declines in blood glucose which precede feeding are causally related to meal initiation under free-feeding conditions. We have also shown that IV infusions of glucose (20 mg) that blunt these declines can delay meal initiation. In order to test the specificity of exogenous glucose to delay meal initiation, the ability of another hexose, fructose, to block meal initiation was studied. Since oral and IV fructose have been reported to cause transient hypoglycemia, we also used fructose in an attempt to mimic transient declines in blood glucose and measure the latency to meal initiation. Continuous monitoring of blood glucose and meal pattern was performed in chronically cannulated female rats. When fructose (20 mg) was infused IV during transient declines in blood glucose, meal initiation occurred with a normal latency. During the early dark phase, IV fructose was followed by a slight decrease at the lowest dose or increase in blood glucose at higher doses and no feeding behavior was observed. In the light phase, however, a transient dose-dependent decrease in blood glucose was observed. Furthermore, three types of blood glucose response patterns were identified. Meal initiation occurred only following changes in the blood glucose trajectory that mimicked the spontaneous transient declines in blood glucose. The other two patterns were not followed by meal initiation. Similar effects on blood glucose were observed following oral administration of a range of fructose doses (0.25-0.75 g) in 2-hour fasted rats.(ABSTRACT TRUNCATED AT 250 WORDS)