We examined the effect of hydroxyethyl starch macromolecule (HES-Pz) pretreatment on microvascular transport of macromolecules in ischemia-reperfusion injury. The rat cremaster was splayed, placed in a Lucite intravital chamber, and suffused with bicarbonate buffer. The clearance of fluorescein isothiocyanate dextran 150 (FITC-Dx 150) was measured as an index of microvascular transport. After determination of baseline data, the muscle was made ischemic for 4 hr by clamping the vascular pedicle and subsequently reperfused for 2 hr. In control animals not subjected to ischemia, clearance of FITC-Dx 150 remained constant throughout the experimental 7-hr period. In saline-treated animals, ischemia-reperfusion increased the clearance of FITC-Dx 150 from 1.8 +/- 0.3 to 9.7 +/- 1.0 microliters/15 min/g by the end of the reperfusion period. Pretreatment with HES-Pz, at a concentration of 6% in a volume of saline equivalent to 10% of blood volume, significantly attenuated the microvascular dysfunction produced by ischemia-reperfusion. The mean ratio of postischemic to baseline clearance of FITC-Dx 150 was 1.28 +/- 0.07 (mean +/- SE) for samples taken from the 30th to the 120th min of reperfusion at 15 intervals. Our data support a beneficial effect of HES-Pz on microvascular transport of macromolecules. The role of leukocyte-endothelium adhesion as an underlying mechanism explaining these results was studied by evaluating the effect of HES-Pz on the ability of thrombin-stimulated human umbilical vein endothelial cells (HUVECs) to bind neutrophils. These experiments demonstrated that thrombin-treated HUVECS bound 229% more indium-111-labeled neutrophils than did similarly stimulated HUVECS treated with HES-Pz (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)