Effect of bromotetramisole on renal phosphate excretion

Levamisole inhibits alkaline phosphatase (ALP) activity in kidney brush border membranes and increases phosphate excretion in vivo in dogs and rats. I-p-Bromotetramisole (I-BR) is a more potent analog of levamisole in regard to inhibition of ALP activity in vitro, but had no effect on phosphate transport by in vitro proximal tubules of the rabbit. Since its effect on phosphate excretion in vivo has not been studied, the present study tested the effects of infusion of I-BR on phosphate excretion in Sprague-Dawley rats. Fractional excretion of phosphate (FEPi) was measured in thyroparathyroidectomized Sprague-Dawley rats before and during a systemic infusion at 0.8 ml/min of 10 mM I-p-Bromotetramisole oxalate (I-BR, n = 6), or the inactive isomer d-p-Bromotetramisole oxalate (d-BR, n = 5). The FEPi increased significantly from 4.7% +/- 0.9% to 13.4% +/- 3.1% in response to I-BR whereas there were no changes in FEPi with inactive d-BR. In conclusion, systemic infusion of I-p-Bromotetramisole increases FEPi in Sprague-Dawley rats.