TSP-induced hemodynamic abnormalities in the ex vivo mesocecum are prevented by anionic polysaccharides. In five sets of experiments, a bolus of SS RBC that had been preincubated with TSP alone at 2.5 μg/mL or preincubated sequentially with CSA, HS, heparin, HDS, or fucoidan at 250 μg/mL followed by TSP at 2.5 μg/mL was infused into the mesocecum vasculature. In each set of experiments, treatment solely with TSP resulted in a significant increase in PRU (*P < .05 to .02, paired t-test) compared with untreated RBC. Pretreatment with CSA (n = 3), heparin (n = 5), or HDS (n = 4) caused a significant decrease in PRU compared with TSP alone (⁺P < .01, < .05, and < .01, respectively, paired t-test). HS (n = 4) and fucoidan (n = 3) had no significant effect.