Numerous studies have demonstrated that reticuloendothelial system (RES) depression induced by colloid blockade increases susceptibility to circulatory shock following trauma and sepsis. Recent data have suggested that this may relate to the failure of the RES to clear potentially embolic material derived from activation of the hemostatic system. The present study thus compared the hypotensive response precipitated by trauma or sepsis with that resulting from induction of intravascular coagulation. Mean arterial blood pressure (MABP) was monitored for 120 minutes after sublethal NCD trauma and after intra-aortic injection of live E coli (approximately 10(10) organisms per rat), E coli endotoxin (0.1 mg/100 gm), or bovine thrombin (10 units/100 gm) in 400-500 gm rats 30 minutes after RE blockade (50 mg/100 gm gelatinized lipid colloid) or saline injection. All rats were anesthetized with sodium pentobarbital. No hypotension was observed in blockaded control rats. After trauma, MABP decreased by 20 minutes after injury and recovered to normal levels by 1 hour post-trauma. MABP decreased in blockaded rats after trauma and remained diminished through 2 hours. After live E coli endotoxin or thrombin, both the normal and the blockaded groups underwent an initial hypotension of similar magnitude. A second period of hypotension was much more pronounced in the RE-blockaded animals. Reduced MABP persisted in these animals through 2 hours. These data indicate that RE blockade enhances the hypotensive response to intravascular coagulation and that resulting from trauma or sepsis. This effect was especially apparent during the second phase of hypotension during sepsis and intravascular coagulation. It was suggested that the RES manifests some protective effect against the agents inducing this secondary hypotensive response.