Effect of Age on Magnesium Deficiency in Rats.

T h e development of hypomagnesaemia in calves to the stage at which tetanic convulsions occur has been shown experimentally by Blaxter, Rook & MacDonald (1954) to be a comparatively slow process. In contrast, hypomagnesaemic tetany can develop in the dairy cow and lactating ewe with great rapidity (Rook & Balch, 1958; L'Estrange & Axford, 1963). The increased speed of the development of the condition in the mature animal may be partly due to its inability to mobilize reserves of magnesium from bone as readily as does the young animal (Wilson, 1960). It was not possible to carry out a controlled experiment to study the lability of M g reserves in the adult bovine owing to the difficulty in providing a Mg-deficient diet that would support rumination, and to the prohibitive cost of slaughtering animals to obtain tissues for analysis. For these reasons we used rats. There have already been several reports on the effect of Mg deficiency on the content of M g in various tissues in the rat. For example, a marked depletion of the Mg content of bone in young rats on a Mg-deficient diet has been described by Duckworth, Godden & Warnock (1940), and MacIntyre & Davidsson (1958), under similar conditions, were unable to detect any loss of Mg from soft tissues other than muscle. In the study to be described here, the effect of maturity on the susceptibility to M g deficiency and on the availability of M g reserves has been investigated by feeding young and adult rats of the same strain on a Mg-free diet for 18 days. The development of hypomagnesaemia was followed during the course of the experiment and, after slaughter, the depletion of Mg reserves was determined by analysis of selected tissues. The calcium, sodium and potassium contents of the tissues of adult rats were also studied to see if there were changes associated with M g deficiency. In addition, the endogenous Mg loss of the adult animals on a Mg-free diet was determined.