A 50-day study of the influence of fluoride (F) and caffeine on carbohydrate metabolism enzymes was conducted on 18 male Sprague-Dawley rats, 4.5 months old, housed in separate cages at 22–25°C on a 12-hr light/dark cycle. The rats were divided into three groups with six rats in each group: control, F, and F+caffeine. F was administered by intubation in water as sodium fluoride (NaF) at a dosage of 4.9 mg F ion/kg bw/day and at the same dosage plus 3 mg caffeine/kg bw/day. After 50 days, the concentration of F in the blood serum was approximately double that of the control group, and the blood glucose increased marginally in the F and F+caffeine groups by 12% and 18%, respectively. In the liver, the activity of sorbitol dehydrogenase (SDH) decreased significantly in the F group by 45% but increased non-significantly in the F+caffeine group by 13%. Also in the liver, the activities of aldolase (ALD) and lactate dehydrogenase (LDH ) in the F group increased by 13% and 16%, respectively, but in the F+caffeine group they decreased by 16% and 4%. In the serum, the activity of SDH increased very significantly in the F and the F+caffeine groups by 212% and 186% , respectively. On the other hand, the activities of ALD and LDH in the F group decreased by 15% an d 52%, respectively, whereas in the F+caffeine group the activity of ALD increased by 17% and the activity of LDH decreased by 70%.
CONCLUSION: In the liver, fluoride (F) ions inhibited the transformation of sorbitol into fructose, whereas caffeine promoted this conversion. Glycolysis in the liver, under the influence of F, did not appreciably change, whereas in the presence of caffeine it was slightly inhibited. Glycolysis in extra-hepatic tissues (serum), under the influence of F, was slightly inhibited; however, it was markedly intensified by caffeine. Overall, a more profound influence by caffeine on carbohydrate enzyme activity was observed in blood serum (extra-hepatic tissues) than in the liver.