Investigation of an inflammatory humoral factor as a stimulator of fibrinogen synthesis.

A purported stimulatory effect on fibrinogen synthesis of pyrogenic crude leukocyte extract (CLE) is controversial. To clarify this issue, a study was made of possible inflammatory cellular or humoral factors as stimulators of fibrinogen synthesis. Relative fibrinogen synthesis ratios were calculated by comparing the rate of incorporation of radiolabeled lysine into fibrinogen with that of incorporation into albumin. Significant increases in the ratio over baseline values were observed in rabbits after i. v. administration of CLE derived from 0.99 – 3. 35×109 homologous leukocytes harvested from inflammed rabbit peritoneal cavities (0.146±0.038 control and 0.249±0.119 after CLE, p<0.01). Wash fluid which was used to collect the peritoneal leukocytes was also infused and found to increase ratios above baseline (0.118±0.052 control and 0.226±0.094 after inflammed peritoneal, wash fluid). This difference, however, was only borderline statistically significant (p = 0.05). In contrast, no significant increases above baseline were observed in the ratio following intravenous administration of 1) blood leukocyte derived CLE, 2) intact blood leukocytes, or 3) plasma, all harvested from turpentine or glycogen injected animals. These data suggest that at inflammatory sites, granulocytes produce a mediator(s) which increases fibrinogen synthesis during inflammation. It is well known that during many types of inflammation plasma fibrinogen concentration increases. However, little is known of the mechanisms which mediate increased fibrinogen synthesis during inflammation. Pyrogenic substances released from rabbit granulocytes have been reported to cause increases in serum acute phase proteins in recipient rats (1–3). These factors, variably called leukocyte endogenous mediator (LEM), leukocyte pyrogen (LP), or crude leukocyte extract (CLE), have also been reported by Bocci (4) to result in an increase in plasma fibrinogen concentration over controls when given in “significant” amounts to homologous recipient rabbits. On the other hand, Seligsohn (5), while using a similar homologous rabbit model, failed to demonstrate a significant increase in plasma fibrinogen concentration or synthesis following CLE administration. With this controversy in mind, we investigated the possible existence of a cellular or humoral stimulator of fibrinogen synthesis during inflammatory states in a homologous rabbit system. As potential sources of mediator, we sampled materials from a site of inflammation. These were crude leukocyte extract derived from leukocytes and wash fluid from the peritoneum after sterile peritonitis was induced in rabbits. In addition, we sampled materials distant from the site of inflammation. These were peripheral blood, buffy-coat leukocytes and plasma as well as crude leukocyte extract derived from buffy-coat leukocytes. The effect of the infusion of these homologous experimental materials on fibrinogen synthesis was measured by determining the relative fibrinogen synthesis rate as adapted from that described by Koj (6). With this technique, the amount of incorporation of radiolabeled lysine into fibrinogen is compared to that of its incorporation into albumin during the same measurement period. Albumin is used since it is a non-inflammatory protein (6). The relative synthesis rate of fibrinogen (fg) versus albumin (alb), or fg/alb ratio, approximates the ratio of the absolute synthesis rate of the two proteins. Unlike techniques following 15Se-methionine incorporation into fibrinogen (7), this method allows sequential use of 3H and 14C-lysine permitting both a baseline control and experimental study in the same animal. Increases above control of this ratio indicates an increase in synthesis rate of fibrinogen. This method also has advantages over measuring changes in fibrinogen concentration, because it is faster and more sensitive.