An Evaluation of Possible Sites of Phosphate Secretion in the Rat Nephron

Abstract

Although net secretion of phosphate has been demonstrated in non-mammalian species, the secretion of phosphate in mammals has been difficult to demonstrate using clearance methods (1). In these studies, plasma phosphate was elevated by infusion of phosphate and the clearance of phosphate was compared to the clearance of a glomerular marker (usually inulin). The results were equivocal with some investigators reporting net secretion, while others did not. In recent studies by Boudry et al (2), phosphate clearances were greater than inulin clearances in conscious rats when plasma Pi concentration was corrected for ultrafilterability. Likewise, in studies by Troehler et al (3), rats fed a high phosphate diet for 10 days and then infused acutely with phosphate, had a FE_p% of 97% without correction for plasma ultrafilterability. Since it is highly unlikely that unidirectional outflux of phosphate (reabsorption) was abolished completely in these studies, this data has been taken as evidence for a secretory component of net phosphate transport if not net secretion per se.