Parathyroid hormone impairs extrarenal potassium tolerance in the rat

The effect of parathyroid hormone (PTH) on the extrarenal disposition of an acute potassium load was examined in acutely nephrectomized rats infused with KCl (0.75 meq.kg-1.h-1 for 90 min) alone or in combination with 8-10 U.kg-1.min-1 PTH, with serial monitoring of plasma potassium every 10 min. The rise in plasma potassium concentration (delta PK) in the PTH group was higher than control. PTH was then administered along with KCl to two groups of nephrectomized and acutely thyroparathyroidectomized (TPTX) rats in doses of 1 and 0.25 U.kg-1.min-1 for 90 min. delta PK with PTH in both groups was higher than TPTX control (P less than 0.01). The two higher doses of PTH resulted in a decrease in mean arterial pressure from their respective controls. A similar reduction in arterial pressure in three groups of nephrectomized rats by administration of hydralazine or nitroprusside or by acute blood loss did not change delta PK subsequent to potassium infusion from that in control rats. Furthermore, the lowest dose of PTH did not lower arterial pressure from its respective control. Therefore, hypotension is not a cause for the PTH-induced potassium intolerance. Serum levels of insulin, aldosterone, catecholamines, calcium, plasma HCO3 concentration, and pH were not different in PTH-infused vs. respective control rats. These data suggest that PTH impairs extrarenal potassium disposal in the rat. The effect of PTH may relate to enhanced calcium entry into cells.