Figure 1. Comparison of normal versus collateral-dependent vessel response to (A) sodium nitroprusside, (B) adenosine 5' diphosphate, and (C) endothelin-1. After preconstriction with U46619, relaxation to sodium nitroprusside was not significantly different between the normal and the CD vessels (P = 0.45). However, the normal vessels dilated to the endothelium-dependent dilator adenosine 5' diphosphate significantly more than the CD vessels (P < 0.001). The CD vessels constricted to endothelin-1 more than the normal vessels (P < 0.01). #P < 0.05 versus corresponding normal vessel response.