COORDINATE REGULATION OF RAT RENAL PARATHYROID-HORMONE RECEPTOR MESSENGER-RNA AND NA-P-I COTRANSPORTER MESSENGER-RNA AND PROTEIN

Parathyroid hormone (PTH) acts on the kidney by binding to the PTH rec eptor, leading to a decrease in the active renal reabsorption of phosp hate by the Na-P-i cotransporter, which is also independently activate d by hypophosphatemia. We have studied the effects of hypo- and hyperp arathyroidism and hypophosphatemia on PTH receptor mRNA and Na-P-i cot ransporter mRNA and protein. Both surgical parathyroidectomy and hypop hosphatemia, which itself leads to hypoparathyroidism, led to an upreg ulation of the PTH receptor mRNA and Na-P-i cotransporter mRNA and pro tein. Parathyroidectomized rats fed a low-P-i diet had an increase in PTH receptor and Na-P-i cotransporter mRNAs. Diet-induced hyperparathy roidism had no effect on PTH receptor mRNA and Na-P-i cotransporter mR NA and protein. The effect of hypoparathyroidism and hypophosphatemia to increase both PTH receptor mRNA and Na-P-i cotransporter mRNA and p rotein shows that there is a tight coordinate regulation of these fact ors, which are both involved in PTH action.