Turnover of human lactoferrin in the rabbit.

Lactoferrin turnover was studied in the rabbit with 125I- and 131I-labelled human lactoferrin. Plasma lactoferrin activity showed a rapid decrease during the first 24 h, followed by a 'final slope' with a T1/2 of about 25 h. Turnover studies after transfer of plasma from one 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 dissapearance from the plasma, there was a marked accumulation of proteinbound activity only in the liver in both A and B rabbits. From these results, the rate of synthesis in normal man can be estimated at around 25 mg per d. The disappearance pattern and hepatic uptake are discussed in relation to knowledge about lactoferrin receptors in macrophages, asialo elimination, and fucose group recognition. Concerning the significance of lactoferrin turnover for iron metabolism it is concluded that the plasma turnover results are insufficient to explain the disturbance in iron kinetics seen in the anaemia of chronic disorders; however, it is likely that lactoferrin plays a role in iron metabolism within the extravascular space.