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

Abstract

The activity of phytase in the proximal part of the small intestine has been measured in rats kept on a variety of diets. In most experiments, the proportion of ash in the bones of the leg was also measured. The diets were based on wheat, on maize or on purified ingredients, alone or with the addition of vitamin D, calcium carbonate, bran, sodium phytate, or a sodium citrate-citric acid mixture. During the induction of rickets there was a fall, and during its healing a rise, both in phytase and in bone-ash content The administration of vitamin D, even with non-rachitogenlc diets, always increased the amount of phytase. The administration of bran or of sodium phytate usually decreased rather than increased the amount of phytase. The enzyme is thus not ''adaptive'', i.e. it is not inducible by its substrate. When the diets contained adequate inorganic phosphorus, there was a relationship between phytase and bone-ash content, determined by the amount of available calcium. Thus, it was affected by vitamin D, phytate and citrate. When the diets contained inadequate inorganic P, bone-ash content was lower for a given amount of enzyme. With the high -Ca rachitogenic diets, the availability of the inorganic P was increased by phytate and by citrate. Both combined with excessivi Ca; in addition, phytate gave an increased amount of inorganic P from its own hydrolysis. Phytate in ordinary diets, consisting of compounds with varying proportions of the cations hydrogen, potassium, magnesium and calcium, can thus have varying effects on calcification. It can increase or decrease available Ca, or increase available inorganic P. The effects on calcification will therefore depend on the other components of the diet.