Dissociation of tubular sites of action of saline, PTH and DbCAMP on renal phosphate reabsorption.

The effects of saline expansion, parathyroid hormone (PTH) administration and dibutyryl cyclic 3'5'-adenosine monophosphate (DbCAMP) infusion on renal phosphate reabsorption were examined in acutely thyroparathyroidectomized (TPTX), phosphate infused dogs by the recollection micropuncture technique. Saline expansion reduced whole kidney phosphate reabsorption from a mean of 66.1 to 50.4% of filtered load. This response was entirely accounted for by an inhibition of proximal tubular phosphate reabsorption which fell from a mean of 35 to 21% of the filtered phosphate load. Both PTH and DbCAMP produced a fall in whole kidney phosphate reabsorption comparable to saline. However, this effect was the sum of inhibition of both proximal tubular and distal nephron phosphate reabsorption. These studies demonstrate the important role of the distal nephron in modulating urinary phosphate excretion.