In‐vivo studies on Haemaccel‐fibronectin interaction in man

. An enzyme‐linked immunoassay has been recently set up for direct measurement of the binding capacity of plasma fibronectin to gelatin. This binding capacity could be completely inhibited in vitro by an eight‐fold excess of gelatin, of Haemaccel®, but not of Geloplasma®. On the contrary, the levels of immunoreactive fibronectin measured by laser nephelometry did not change, in presence of 10 to 1000 μg ml −1 of gelatin, of Haemaccel or of Geloplasma. When infused into normal volunteers, Haemaccel provoked a strong and immediate inhibition of the plasma fibronectin binding capacity to gelatin. This inhibition was dose‐dependent and maximal after infusion of 500 ml of Haemaccel. Twenty‐four hours after this infusion, there was a progressive recovery of the gelatin‐binding capacity, which was almost completely achieved 96 h later. The formation of complexes between Haemaccel and fibronectin was demonstrated by gel filtration chromatography and by affinity chromatography. Immunoreactive plasma fibronectin levels remained unchanged up to 24 h after infusion of 500 ml of Haemaccel. A transient decline to 50% of its initial value then occurred the second day after the infusion. Therefore, a delay existed between the formation of fibronectin‐Haemaccel complexes and their elimination from the bloodstream. This delay decreased when smaller volumes of Haemaccel were infused, which strongly suggests that plasma fibronectin is cleared by means of Haemaccel and does not seem to play a role of opsonin in these conditions. Besides, after Haemaccel infusion, the recovery time of the gelatin binding function of plasma fibronectin most probably reflects the blood turnover of this domain of the molecule. The production rate of new fibronectin molecules appears to be about 90 μg ml −1 day −1 , which corresponds to a half‐recovery time of about 40 h.