Effect of magnesium deficiency on rat bone and kidney sensitivity to parathyroid hormone

A series of six experiments was conducted to investigate the effects of Mg deficiency in the young rat on parathyroid hormone (PTH) activity and on response to parathyroid extract (PTE) and to endogenously produced PTH stimulated by dietary Ca deficiency. Major criteria employed were 45Ca release from pre-labeled bone and urinary excretion of cAMP. Mg deficiency was accompanied by lowered 45Ca mobilization and urinary cAMP excretion, indicating either a depression in PTH secretion or tissue insensitivity to it. Administration of PTE resulted in equivalent increases in 45Ca mobilization irrespective of Mg status but increased cAMP excretion only in Mg-adequate animals, thus indicating a depressed sensitivity of kidney to PTH in the Mg-deficient animal. In vitro response of kidney cortex from Mg-deficient animals to PTE added to incubation medium indicated no defect in the adenyl cyclase system. Endogenous stimulation of PTH by low Ca diet increased cAMP in Mg-adequate animals but not in rats with pre-existing Mg deficiency. Mg deficiency did not reduce cAMP previously stimulated by Ca deficiency.