Microbial flora in the digestive tract and action of lactose on mineral metabolism.

Germ-free (GF) and conventional (CV) adult rats were given for 4 weeks a semi-synthetic diet containing 10 p. 100 lactose (L) or no lactose (LO). The axenic state had an unfavourable effect on sodium and potassium absorption. On the contrary, it increased the absorption and retention of calcium, phosphorus and magnesium. The favourable effect of lactose on magnesium metabolism was not different in GF and CV rats. On the contrary, lactose increased the absorption and retention of phosphorus and calcium more in GF than in CV animals. It augmented the amount of calcium present in a soluble, ultrafiltrable form in the caecum of only the GF rats. These results are discussed and compared to previous data on younger rats. They lead to the hypothesis that the voluminous caecum of the GF rat is the site of a calcium absorption which is accentuated by presence of lactose in the diet.