Response at the microvascular level: vessel diameter, blood flow, and perivascular NO levels. (A) NOS inhibition. Significant vasoconstriction, loss of perfusion, and reduced perivascular NO levels were obtained (P < .05). (B) CFH concentration. The microvascular response was not a function of the CFH concentration. Significant decrease in arteriolar diameter, microvascular blood flow, and perivascular NO were obtained with both PBH and PBH4 (P < .05). (C) CFH molecular configuration. The smaller CFH molecules (ααHb and PBH4) caused arteriolar constriction leading to reduced microvascular perfusion compared with baseline and MP4. MP4 was not vasoconstrictive and had increased arteriolar blood flow. All CFHs reduced perivascular NO to similar levels relative to saline (P < .05). and ▪ denote the arterioles and venules, respectively. Blood flow data are shown as mean ± SEM. Parameters are present as relative to baseline, thus no change from baseline would be denoted as 1, while 1.1 would mean a 10% increase from baseline. ^* and ^** denote a statistical significant difference relative to saline and MP4, respectively.