Effects of Poly-[gamma]-glutamic Acid on Calcium Absorption in Rats

The effects of poly-γ-glutamic acid (γ-PGA) on calcium (Ca) bioavailability and Ca content in bone were examined in female rats. Increases in in vitro Ca solubility was observed with increases in the amount of γ-PGA. Acute studies showed that γ-PGA increased the amount of soluble Ca in the small intestine. In a plasma-Ca kinetic experiment, γ-PGA stimulated Ca absorption 20 min after administration, and the duration of absorption was approximately 2 h. In an acute intestinal transit experiment, γ-PGA markedly increased intestinal transit in mice. In a chronic Ca-balance experiment, the results showed that γ-PGA significantly increased the apparent Ca absorption, apparent Ca balance, bone density, and bone Ca content in rats. In the same experiment, γ-PGA was also found to decrease the amount of soluble Ca in the small intestine, especially in the proximal small intestine, and to increase calbindin-D9k mRNA expression in the proximal small intestine in rats. In a chronic intestinal transit experiment, γ-PGA decreased intestinal transit in mice. These results suggest that γ-PGA increased Ca solubility, thereby enhancing Ca absorption in rats in the acute phase. In addition, chronic administration of γ-PGA to rats increased the apparent Ca balance and bone Ca content. The active transcellular pathway in the proximal small intestine was the major mechanism by which these effects were exerted.