Contribution of hepatic fibronectin synthesis to regulation of plasma fibronectin.
Intravenous injection of gelatinized particles, which are phagocytized by the reticuloendothelial system, elicits an acute depletion of plasma fibronectin followed by restoration to normal concentrations in 6-8 h and a rebound elevation at 24 h. We determined the contribution of hepatic fibronectin synthesis to the restoration of plasma fibronectin in rats after particle infusion by measuring the net incorporation of 75selenomethionine into plasma fibronectin during the recovery period. Rats injected intravenously with gelatinized particles had a greater (P less than 0.01) incorporation of labeled 75selenomethionine into fibronectin but less (P less than 0.05) incorporation of 75selenomethionine into total plasma protein than control rats. Inhibition (86%) of hepatic fibronectin synthesis by pretreatment with cycloheximide limited the recovery of fibronectin levels by only 60%, suggesting a source(s) other than hepatic synthesis may contribute to the restoration of plasma fibronectin. Using purified human plasma fibronectin as a tracer in the plasma pool, we found that 26% of the soluble fibronectin consumed from the plasma during particle clearance was subsequently released back into the plasma over a 4-h interval. Tissue analysis indicated that 125I-labeled fibronectin, which was previously incorporated into the tissues, was not released from the tissue pool after the injection of gelatinized particles. Thus the normalization and regulation of plasma fibronectin levels after its acute depletion due to blood-borne particles is a result of 1) an increase in hepatic synthesis of fibronectin, 2) the release of fibronectin previously consumed as an opsonin during particle clearance, and 3) the release of soluble intact fibronectin from a preformed storage pool.
Vincent
P A
PA
Department of Physiology, Albany Medical College, New York 12208.
Saba
T M
TM
Lewis
E
E
Cho
E
E
D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D004655:Emulsions; D005353:Fibronectins / Q000096:biosynthesis* / Q000097:blood / Q000172:deficiency; D006706:Homeostasis; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D012157:Mononuclear Phagocyte System / Q000502:physiology; D009928:Organ Specificity; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D012645:Selenomethionine / Q000378:metabolism
D004655:Emulsions; D005353:Fibronectins; D012645:Selenomethionine; D003513:Cycloheximide