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 facilitates the absorption of iron from lactoferrin. Our aim in this study was to evaluate the ontogeny and localization of lactoferrin receptors 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 and receptor density were determined in relation to the age of the piglet (day 0-21 after birth) and the location (duodenum, jejunum, and ileum) within the small intestine. Specific and saturable binding of ⁵⁹Fe-labelled pig lactoferrin by brush border membranes purified from piglet intestine was observed. Pig transferrin, human, and bovine lactoferrin did not bind to the porcine lactoferrin receptor. Lactoferrin binding occurred throughout the intestine independent of age of the piglet; receptor number (15 × 10¹⁴/mg protein) and affinity (K_d = 3 × 10-7 M) were relatively constant from birth until weaning. Thus, it is possible that lactoferrin receptors throughout the intestine may play a role in iron absorption throughout infancy.