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  • Title: Differences in effects of amino-terminal and intact parathyroid hormone on calcium, phosphate, and cAMP excretion by the isolated perfused rat kidney.
    Author: Besarab A, Swanson JW.
    Journal: Ren Physiol; 1982; 5(6):261-71. PubMed ID: 6294762.
    Abstract:
    Urinary cAMP (UcAMP) reflects activation of renal adenylate cyclase by parathyroid hormone (PTH). UcAMP excretion and the phosphaturic, anticalciuretic responses to bovine PTH by a stable isolated perfused rat kidney were compared. Dose-response curves were obtained for two synthetic amino-terminal [1-34] PTH preparations and three highly purified intact [1-84] PTH preparations. With all preparations, anticalciuria occurred at lower concentrations (less than 10(-10) M) than those needed to produce a significant increase in UcAMP excretion or phosphate excretion. Maximal decreases in calcium clearance with [1-34] PTH were independent of concentrations between 10(-10) and 10(-7) M whereas cAMP and phosphate increased sigmoidally at PTH concentrations above 10(-10) M. The two synthetic [1-34] PTH preparations had identical anticalciuretic and phosphaturic dose-response curves despite their significantly different effects on cAMP excretion. Intact [1-84] PTH concentration-response curves were identical to those of [1-34] PTH at concentrations less than 3 x 10(-9) M. At higher concentrations, phosphaturia was greater and anticalciuria blunted compared to [1-34] PTH. These latter changes were associated with natriuresis and kaliuresis, effects not seen with [1-34] PTH. The isolated kidney may be a useful model for further studies of PTH action and also constitutes a bioassay system to evaluate hormone potency.
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