Recovery of renal tubule phosphate reabsorption despite reduced levels of sodium-phosphate transporter.
BACKGROUND
The acute effect of parathyroid hormone (PTH) on phosphate transport has been reported to be mediated by rapid downregulation of sodium-phosphate transporter (NaPi-IIa) protein, but the association was observed with pharmacological doses of PTH.


OBJECTIVE
To explore the effects of physiological doses of PTH on NaPi-IIa protein and its relationship to phosphate transport.


METHODS
Acute clearance studies were performed in parathyroidectomized rats given a bolus i.v. physiological dose (1 microg) of bovine PTH(1-34) and NaPi-IIa protein concentrations were examined at different time intervals.


RESULTS
Fractional excretion of phosphate increased from 0.031+/-0.006 (mean+/-S.E.) to 0.238+/-0.059 (P<0.01 compared with baseline and compared with controls) at 40 min and returned to control values by 120 min. Urinary cAMP concentrations were increased at 20 min only. Superficial cortex brush-border membrane (BBM) NaPi-IIa protein was decreased from baseline at both 40 and 120 min (P<0.01) and did not recover at 240 min (P<0.01 compared with baseline and compared with controls).


CONCLUSIONS
These results confirm that PTH, even in physiological dosage, causes a rapid decrease in BBM NaPi-IIa, but subsequent recovery of phosphate reabsorption is poorly correlated with BBM concentrations of NaPi-IIa protein. This suggests that transport mechanisms other than NaPi-IIa are important in renal phosphate reabsorption.
Friedlaender
Michael M
MM
Nephrology and Hypertension Services, Hadassah University Hospital, Jerusalem, Israel 91120.
Wald
Hanna
H
Dranitzky-Elhalel
Michal
M
Levi
Moshe
M
Popovtzer
Mordecai M
MM
D000042:Absorption; D000818:Animals; D002118:Calcium / Q000097:blood; D003404:Creatinine / Q000378:metabolism; D000242:Cyclic AMP / Q000652:urine; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D007684:Kidney Tubules / Q000378:metabolism*; D008297:Male; D008871:Microvilli / Q000187:drug effects; D010281:Parathyroid Hormone / Q000494:pharmacology; D016105:Parathyroidectomy; D010710:Phosphates / Q000097:blood / Q000378:metabolism*; D051381:Rats; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters / Q000378:metabolism*
D010281:Parathyroid Hormone; D010710:Phosphates; C493556:Slc34a1 protein, rat; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters; D003404:Creatinine; D000242:Cyclic AMP; D002118:Calcium