Comparison of effects of dietary calcium and magnesium depletion on renal glucose-6-phosphatase activity of rats fed high protein and high carbohydrate diets.

In order to determine the relationship between renal gluconeo- genesis and calcium status of the body, the effects of low levels of dietary calcium and magnesium on growth rate, food intake, serum and renal calcium concen trations and activities of hepatic and renal glucose-6-phosphatase (GGPase) of rats were investigated under the conditions of feeding a high protein or a high carbohydrate diet. Calcium depletion caused significant decreases in the growth rate and food intake of rats fed the high protein diet, while in rats fed the high carbohydrateâ€"low calcium diet no significant changes were observed. Feeding the low magnesium diets caused marked decreases both in the growth rate and food intake of rats compared with those of corresponding control dietary groups. The activity of renal G6Pase was increased remarkably by feeding the low cal cium diets, while the hepatic activity of the enzyme did not show any significant change in either of these dietary groups. The stimulative effects of both high dietary protein and low dietary calcium on the activity of renal GSPase were additive. On the other hand, magnesium depletion produced lower activities of renal GBPase than those of rats fed the corresponding control diets on a gram wet weight basis. Levels of serum calcium tended to decrease in groups fed the low calcium diets, while those of groups fed the low magnesium diets tended to increase compared with those of corresponding control dietary groups. Higher susceptibility of rats fed the high protein diet to calcium depletion compared with rats fed the high carbohydrate diet led to the consideration that the effect of the high protein diet on the activity of renal G6Pase might be related to changes in calcium status of the body. J. Nutr. 102: 1615-1622, 1972.