Fluoride Alteration of [3H]Glucose Uptake in Wistar Rat Brain and Peripheral Tissues

Abstract

The present study was designed to investigate the role of postnatal fluoride intake on [3H]glucose uptake and transport in rat brain and peripheral tissues. Sodium fluoride (NaF) in a concentration of 10 or 50 ppm was added to the drinking water of adult Wistar rats. The control group received distilled water. After 4 weeks, respective plasma fluoride levels were 0.0541 ± 0.0135 μg/ml (control), 0.0596 ± 0.0202 μg/ml (10 ppm), and 0.0823 ± 0.0199 μg/ml (50 ppm). Although plasma glucose levels were not altered in any group, the plasma insulin level in the fluoride (50 ppm) group was elevated (0.72 ± 0.13 μg/ml) versus the control group (0.48 ± 0.24 μg/ml) and fluoride (10 ppm) group. In rats receiving fluoride for 4 weeks at 10 ppm in drinking water, [3H]glucose uptake was unaltered in all tested parts of the brain. However, in rats receiving fluoride at 50 ppm, [3H]glucose uptake in cerebral cortex, hippocampus, and thalamus with hypothalamus was elevated, versus the saline group. Fluoride intake had a negligible effect on [3H]glucose uptake by peripheral tissues (liver, pancreas, stomach, small intestine, atrium, aorta, kidney, visceral tissue, lung, skin, oral mucosa, tongue, salivary gland, incisor, molars, and jawbone). In neither fluoride group was glucose transporter proteins 1 (GLUT 1) or 3 (GLUT 3) altered in frontal cortex and striatum versus control. On the assumption that increased glucose uptake (by neural tissue) reasonably reflects neuronal activity, it appears that fluoride damage to the brain results in a compensatory increase in glucose uptake and utilization without changes in GLUT 1 and GLUT 3 expression.

Keywords: Brain; Exposure; Fluoride; Glucose transporter; Glucose uptake; Rats.

Fig. 1

Fluoride intake and plasma fluoride concentration in adult rats exposed to NaF in drinking water in a concentration of 10 or 50 ppm (n = 8). Control, NaF 10 ppm, NaF 50 ppm; # indicates p < 0.05

Fig. 2

Glucose and insulin plasma concentrations in adult rats exposed to fluoride in drinking water in concentrations of 10 or 50 ppm (n = 8). Control, NaF 10 ppm, NaF 50 ppm; # indicates p < 0.05

Fig. 3

[³H]glucose uptake in the brain in adult rats exposed to NaF in drinking water, at a concentration of 10 or 50 ppm (n = 6). Control, NaF 10 ppm, NaF 50 ppm; # indicates p < 0.05

Fig. 4

GLUT 1 and GLUT 3 protein immunoreactivity, assessed densitometrically in frontal cortex slices of adult rats exposed for 4 weeks to NaF in drinking water in a concentration of 10 or 50 ppm (n = 7). Control, NaF 10 ppm, NaF 50 ppm; # indicates p < 0.05

Fig. 5

GLUT 1 and GLUT 3 protein immunoreactivity, assessed densitometrically in striatum slices of adult rats exposed for 4 weeks to NaF in drinking water in a concentration of 10 or 50 ppm (n = 7). Control, NaF 10 ppm, NaF 50 ppm; # indicates p < 0.05