Time- and dose-related biphasic effects of synthetic bovine parathyroid hormone fragment 1-34 on urinary cation excretion.

The reported effects of PTH on urinary excretion of cations are highly variable. We investigated dose and time relationships for urinary clearance of calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K) after infusions of synthetic bovine PTH fragment 1-34 [bPTH-(1-34)] in seven normal subjects. The bPTH-(1-34) was given over 15 min on widely separated days at doses of 10, 30, 75, 150, and 300 U/70 kg. The 75, 150, and 300 U/70 kg doses produced a biphasic excretory pattern for all four ions, with increased clearance from 0-30 min and enhanced reabsorption at 60-120 min. Lower doses produced only retention of Ca, Mg, and Na, but even 10 U bPTH-(1-34)/70 kg caused a marked biphasic excretory pattern of K. These data explain why in previous studies PTH increased, decreased, or had no effect on the excretion of divalent and monovalent cations and emphasize the importance of short, clearly defined urine collection intervals for in vivo studies of PTH action of the kidney.