Strontium and its relation to calcium metabolism.

Strontium and Ca metabolism were compared in man without, at the same time, assuming any metabolic relationship between these elements. A set of parameters was developed that have the same formal significance for each element. Present knowledge of Sr metabolism is as yet inadequate to permit affirming whether or not this element behaves in the body as if there were a central pool of constant size. Calcium, on the other hand, is known to have such a central pool. To avoid making any assumption concerning such a pool, each of the body processes (over-all loss, urinary excretion, fecal excretion, and bone uptake) was expressed in terms of its characteristic rate constant. This constant is independent of the real scheme of Sr metabolism. It has tbe drawback of being much less explicit for a given process than would be a true rate, expressed in units of mass per unit time. It is the only one, however that allows describing Sr metabolism and comparing it with Ca metabolism. Results are presented from a comparison of the Sr and Ca rate constants of the various processes in 15 studies done on 8 patients whose Ca metabolism differed widely. The findings are interpreted tomore » mean that, qualitatively, both Sr and Ca follow the same metabolic pathways, and quantitatively, the use of Sr as a tracer for Ca in a given indvidual leads only to an approximation of the true value, the degree of error varying unpredictably for a particular case. Whereas all of the parameters of Ca metabolism can be evaluated in terms of unit mass and unit mass per unit time by the combined use of the Ca balance and Ca/sup r/, the use of Sr in studies of Ca metabolism can yield information only in terms of an apparent circulating volume and of rate constants. Strontium may be used as a tracer for Ca to measure the mean bone formation rate in groups of individuals whose Ca metabolism is disparate. (auth)« less