Indirect effect of casein phosphopeptides on calcium absorption in rat ileum in vitro

― Casein phosphopeptides (CPP) are the phosphorylated fragments of bovine milk casein. They are believed to enhance intestinal absorption of calcium by their ability to form soluble complexes with calcium thereby inhibiting the precipitation of phosphate-calcium salts. In order to evaluate whether they also act in an additional direct manner on the intestinal mucosa, these peptides were added in a phosphate-free medium at a concentration of 1, 2, or 4 mg/ml on the mucosal side of rat ileum mounted in an Ussing chamber in vitro. No effect on the electrical parameters of the tissue was observed. The unidirectional mucosal-to-serosal flux of calcium was significantly reduced in the presence of the peptides, without alteration in the serosal-to-mucosal flux. Jms was 51.71 2.67 pEq/h.cm 2 for control vs. 19.23 3.95 in the presence of 4 mg/ml CPP. This effect was associated with a reduction in free calcium in the mucosal reservoir of the Ussing chamber, without modification of mucosal total calcium or of serosal total and free calcium. These results indicate that CPP did not directly act on rat ileum to enhance calcium absorption. These peptides bind calcium, and the CPP-calcium complex which was not efficiently absorbed remained on the mucosal side of the tissue. In these conditions, the physiological role of CPP on intestinal calcium absorption could be only an indirect luminal inhibition of the precipitation of phosphate― calcium salts. This effect remains to be clearly established. milkintestinepeptide -transport Rsum ― Action indirecte des phosphopeptides de casines sur l'absorption du calcium par l'ilon de rat in vitro. Les phosphopeptides (CPP) de casines sont des fragments phosphoryls extraits des casines du lait de vache. Il a t montr que ces peptides qui fixent le calcium taient susceptibles de stimuler l'absorption du calcium dans l'ilon de rat in vivo, probablement en inhibant la prcipitation de phosphates de calcium. Afin de vrifier si ces peptides n'ont pas aussi une action directe sur la muqueuse intestinale, ils ont t introduits la concentration de 1, 2 ou 4 mglml sur le versant muqueux de l'ilon de rat mont en chambre de Ussing in vitro dans un milieu sans phosphate. Aucun effet sur les paramtres lectriques du tissu n'a pu tre observ. L'addition des CPP provoque, en revanche, une rduction significative du flux unidirectionnel de calcium muqueux-sreux, sans modification du flux inverse sreux-muqueux. Le flux Jms est de 51,71 2,67,uEqlh.cm 2 dans une chambre tmoin, et de 19,23 t 3,95 en prsence * Author to whom correspondence should be addressed.