Effect of phytate and other dietary factors on intestinal phytase and bone calcification in the rat

The work described here began as an extension of our previous studies on enzyme induction.We were interested to see whether an increase in dietary phytate resulted in an increase in intestinal phytase.This question is of particular interest in relation to the effects of diets rich in phytate on calcium absorption in man.Walker, Fox & Irving (1948), amongst others, have claimed that an increase in dietary phytate produces only a temporary loss of Ca from the body; after a few weeks, Ca begins to be retained again.One way in which this adaptation could occur would be by an increased destruction of phytate, caused by an increased amount of phytase evoked by the increased dietary phytate.There is a great deal of published work on phytate and on plant phytases, but little on intestinal phytase.This enzyme was first reliably demonstrated in rats by Patwardhan (1937).Some of its properties were defined by Spitzer & Phillips (1945).A study of the effects of some dietary changes showed only that phytase activity existed in the presence or absence of vitamin D, or of inorganic or bound phosphorus (Spitzer, Maruyama, Michaud & Phillips, 1948).A more detailed study of the effects of vitamin D in a variety of diets was made by Steenbock, Krieger, Wiest & Pileggi (1953) and by Pileggi, De Luca & Steenbock (1955).In all instances, vitamin D increased the amount of intestinal phytase, but there was no evident relationship between enzyme activity and the severity of rickets when the rats were given rachitogenic diets.Pileggi, De Luca, Cramer & Steenbock (1956) showed that the addition of citrate to the diet reduced the amount of intestinal phytase.Thus, although we were chiefly concerned with the effects of dietary phytate on the amount of intestinal phytase, we extended our study to cover the effects of other dietary factors such as vitamin D and Ca.Since these all affect bone calcification, we included measurements of bone ash in most of our experiments. EXPERIMENTAL A N D RESULTS AnimalsHooded rats of the Lister strain were used.They were weaned at 23 days and given ground stock diet and milk for 24 h.From 24 days onwards they were fed on the experimental diets.For some of the preliminary experiments, and for the experiments on the induction and healing of rickets, the animals were kept on sawdust, six to eight 29