Chu J. Chen

Calcium, magnesium and the control of PTH secretion.

Abstract Critical to the regulation of mineral ion homeostasis is the inverse relationship bewtween the extracellular calcium (Ca2+) concentration and PTH secretion (Fig. 1). Early studies in vivo [1] and in vitro [2] demonstrated that high magnesium (Mg2+) concentrations also inhibit PTH release. At low concentrations, on the other hand, the effects of Ca2+ and Mg2+ on PTH secretion differ: while hormonal secretion persists for an hour or more even at vanishingly low Ca2+ concentrations [3,4], Connie Anast and his co-workers were the first to demonstrate that low Mg2+ concentrations inhibit PTH secretion [5]. In these classical studies, Dr Anast was able to use detailed clinical observations in a single patient to draw important pathophysiological conclusions. Indeed, in the ensuing years, only limited progress has been made in extending these observations to elucidate the cellular mechanisms underlying the inhibition of PTH release at low Mg2+. Considerable advances, on the other hand, have been made in understanding the control of PTH release by high Ca2+ and Mg2+ concentrations. These studies will be reviewed here and provide, in turn, a conceptual framework within which to consider the effects of low Mg2+ on PTH secretion.