Turnover of Human Lactoferrin in the Rabbit

Abstract

Lactoferrin turnover was studied in the rabbit with 125I- and 131I-labeled human lactoferrin. Plasma lactoferrin activity showed a rapid decrease during the first 24 h, followed by a ''final slope'' with a T 1/2 [half time] of about 25 h. Turnover studies after transfer of plasma from 1 rabbit (A) 3 h after injection to another rabbit (B), showed a recovery of 100% compared to 30% in A rabbits but otherwise a similar disappearance curve. The rapid turnover was confirmed in whole body studies. Concomitantly with the initial disappearance from the plasma, there was marked accumulation of proteinbound activity only in the liver in A and B rabbits. From these results, the rate of synthesis in normal man could be estimated at around 25 mg/day. The disappearance pattern and hepatic uptake were discussed in relation to knowledge about lactoferrin receptors in macrophages, asialo elimination and fucose group recognition. Concerning the significance of lactoferrin turnover for Fe metabolism, plasma turnover results were insufficient to explain the disturbance in Fe kinetics seen in the anemia of chronic disorders; lactoferrin probably plays a role in Fe metabolism within the extravascular space.