LACTOFERRIN RECEPTORS IN PIGLET SMALL-INTESTINE - LACTOFERRIN BINDING-PROPERTIES, ONTOGENY, AND REGIONAL DISTRIBUTION IN THE GASTROINTESTINAL-TRACT

Bioavailability of iron from human milk is known to be high. This may be due to a receptor-mediated mechanism in the small intestine that fa cilitates the absorption of iron from lactoferrin. Our aim in this stu dy was to evaluate the ontogeny and localization of lactoferrin recept ors within the small intestine. The piglet was used as an animal model because lactoferrin is a major iron-binding protein in both human and porcine milk. Kinetics of lactoferrin interaction with its receptor a nd receptor density were determined in relation to the age of the pigl et (day 0-21 after birth) and the location (duodenum, jejunum, and ile um) within the small intestine. Specific and saturable binding of Fe-5 9-labelled pig lactoferrin by brush border membranes purified from pig let intestine was observed. Pig transferrin, human, and bovine lactofe rrin did not bind to the porcine lactoferrin receptor. Lactoferrin bin ding occurred throughout the intestine independent of age of the pigle t; receptor number (15 x 10(14)/mg protein) and affinity (K(d) = 3 x 1 0(-7) M) were relatively constant from birth until weaning. Thus, it i s possible that lactoferrin receptors throughout the intestine may pla y a role in iron absorption throughout infancy.