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Five-hour time-concentration curves were obtained after injection of T-1824, I131-labeled human albumin, and I131-labeled dog fibrinogen. The albumin and fibrinogen curves can be roughly divided into 3 segments (0–20 min, 20–70 min, and 70–310 min), each showing a different mean slope. The T-1824 curves show only one change in slope, at 20 min. After at least 70 min the dye left the circulation at a much greater rate than either of the iodinated proteins. Thoracic duct lymph return indicated that 12.9% of the injected iodinated albumin, 8.3% of the T-1824, and 6.3% of the iodinated fibrinogen was returned over the 310-min period. The spaces measured by the T-1824 and the iodinated albumin were not significantly different, whereas the fibrinogen measured a significantly smaller space than either of the former. It is inferred that the dye-protein complex might be broken within the vascular system. Also, the loss of fibrinogen from the capillary is less han for the iodinated albumin.

Several studies have shown that injection of endotoxins causes the plasma fibrinogen level to rise (1-51). Fibrinogen is apparently synthesized in parenchymal cells in the liver (6) and secreted into the lymph (7,8). The regulatory mechanism for the plasma fibrinogen level is not understood. Perfusion studies have indicated that the rate of synthesis depends upon the level of fibrinogen in the blood (9), but observations in vivo failed to show any relation between an elevated fibrinogen level and rate of synthesis In the present work it is shown that in rats the fibrinogen level rises abruptly starting about 8 hr after injecting a small dose of endotoxin subcutaneously. The rate of incorporation of glycine-lT also increases markedly during the period from 8 to 16 hr after injection of the endotoxin. It is suggested that some step in the cellular reaction to inflammation initiates the increase in the plasma fibrinogen level.Materials and Methods. Animals. Young adult female rats of the Carworth Wistar CFN strain were used. They weighed from 150 to 225 g. They were kept in individual cages to which they were accustomed for several days prior to the experiment.Sampling. Blood samples were drawn from the heart under ether anesthesia. For dose response experiments, 0.5 ml of blood was mixed in the syringe with 0.05 ml of 0.1 M sodium citrate. For experiments requiring serial samples from the same rats 0.2 ml of blood was mixed with 0.3 ml of isotonic buffer. The buffer is prepared from MacI1vaine's buffer at pH 6.6 by diluting in the proportion of 3 vol of buffer to 1 vol of water. The packed cell volume is measured and this enables calculation of the extent of (8).dilution of the plasma. Further details were published previously ( 10).Fibrinogen assay. Plasma fibrinogen was determined either by a microgravimetric method (11) or by a heat-turbidity procedure. The heat-turbidity procedure involved mixing 0.1 ml of plasma or 0.2 ml of diluted plasma with 6.0 ml of MacIlvaine's buffer a t pH 5.2. The mixture was heated at 55" for about 20 min. The resulting turbidity was measured as absorbance at a wavelength of 400 nm and converted to fibrinogen concentration by using a reference chart. This was a plot of heat turbidity vs. the concentration of fibrinogen as determined by a gravimetric reference procedure (12).Endotoxins. Bacterial polysaccharides (Difco) from five bacteria were used s e prately for dose response experiments. The polysaccharides were from Serratia marcescens, Escherichia coli, Staphylococcus aureus, Sdmonella typhosa, and Salmonella t yphimuri-The Difco polysaccharides were dissolved or suspended in physiological saline at a concentration of 300/pg/ml. Subcutaneous injections were made with the desired amount in 1.0 ml of saline.Glycine-'4C incorporation. In order to study the rate of incorporation of labeled glycine into fibrinogen a t different times after injection of polysaccharide, the first 24 hr were divided into three periods of 8 hr each. Serratia, marcescens polysaccharide (30 pg/ rat) was inj...

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A procedure is presented for the assay of fibrinogen in small samples of blood. A 0.2-ml. sample of whole blood is mixed in the syringe with 0.3 ml. of isotonic citrate-phosphate buffer and centrifuged in special tubes in which the cell volume is measured. From these measurements the dilution of the supernatant plasma is calculated. The plasma is assayed for fibrinogen and this result is corrected for dilution. Plasma fibrinogen values obtained in this way are comparable to those obtained with other methods that require larger samples of whole blood.