Evidence for skeletal resistance to parathyroid hormone in magnesium deficiency. Studies in isolated perfused bone.

Hypocalcemia during magnesium (Mg) depletion has been well described, but the precise mechanism(s) responsible for its occurrence is not yet fully understood. The hypocalcemia has been ascribed to decreased parathyroid hormone (PTH) secretion as well as skeletal resistance to PTH. Whereas the former is well established, controversy exists as to whether or not Mg depletion results in skeletal resistance to PTH.

Metabolism of parathyroid hormone by fetal rat calvaria.

These studies examine the metabolism of highly purified bovine parathyroid hormone [bPTH-(1--84)] by fetal rat calvaria. Enzymatically dispersed bone cells and intact (minced) calvaria were incubated with bPTH-(1--84) and the incubation medium was analyzed for degradation of PTH by polyacrylamide gel electrophoresis. Eluates of gel slices were assayed for immunoreactive PTH (iPTH) in carboxy- and amino-terminal RIAs.

Selective uptake of the synthetic amino terminal fragment of bovine parathyroid hormone by isolated perfused bone.

Studies from our laboratory have shown that the metabolic clearance rate of carboxy terminal immunoreactive parathyroid hormone (i-PTH) can be accounted for by extraction of i-PTH by liver and kidney. In contrast, there was no demonstrable hepatic uptake of the synthetic amino terminal bovine PTH fragment (syn b-PTH 1-34) and the kidney accounted for only 45% of the metabolic clearance rate of amino terminal i-PTH. This suggested that another major site, presumably bone, played a role in the metabolism of syn b-PTH 1-34.