Effects of fluoride on membrane permeability and brush border enzymes of rat intestine in situ

The effect of different concentrations of sodium fluoride (12, 24, 48 and 96 mm), instilled into the ligated intestine of anaesthetized rats for 30 min, on intestinal permeability and some brush border enzymes was investigated. A concentration-dependent change in permeability was observed; there was an increase in the volume of luminal fluid and altered net transport of Na⁺ and K⁺ ions. The change in permeability was accompanied by increased protein, sialic acid and nucleic acid accumulation in the luminal fluid. A striking loss of brush border alkaline phosphatase (41%) sucrase (59%) and γ-glutamyl transpeptidase (73%) activities was observed at 96 mm fluoride with a corresponding increase in the activity of these enzymes in luminal fluid, while 12 mm fluoride did not produce any significant effect. This loss was probably not due to an inhibition of the enzymes by fluoride since in vitro experiments did not produce any such effect over a range of NaF concentrations (0-32 mm) except on alkaline phosphatase activity at the 32 mm NaF concentration. The studies, therefore, suggest that the loss of brush-border enzyme activities observed in situ was most probably due to membrane damage caused by the high fluoride concentration.