ABSTRACT
Secondary hyperparathyroidism has been attributed to be responsible for the generalized aminoaciduria and phosphaturia of vitamin D deficiency. Since PTH acts in the kidney to generate cAMP, we explored the possibility that its synthetic analog, dbcAMP, would alter the renal transport of taurine (an amino acid lost in the urine in vitamin D deficiency) and Pi. Exposure of renal BBMV prepared from normal and vitamin D-calcium-deficient rats to dbcAMP at concentrations ranging between 10(-4) and 10(-7) M did not alter taurine uptake by these vesicles. Higher dbcAMP concentrations blunted uptake, but these concentrations reduced intravesicular volume, thus representing an artifact of osmolarity. Preincubation of BBMV with dbcAMP for times between 0 and 60 min at 0 or 25 degrees C also did not alter taurine accumulation. Hypotonic lysis of BBMV, allowing entry of the cyclic nucleotide, followed by isotonic resealing did not influence taurine uptake. The addition of potassium fluoride (to inhibit phosphodiesterase activity) and ATP (as an energy source) did not alter taurine accumulation at 60 sec. The uptake of Pi, which is influenced by PTH, was decreased by 25% following exposure to dbcAMP on the internal surface of the vesicle. These data indicate that the taurinuria observed in vitamin D deficiency is unlikely to be related to a PTH-induced increase in intracellular cAMP, unlike the changes in Pi transport, which is sensitive to cyclic nucleotides.
