Different reactivity of the proximal and distal segments of the radial artery to vasoconstrictors in patients undergoing coronary artery bypass grafting

BACKGROUND: Complete arterial revascularisation using the radial artery (RA) is an attractive alternative to venous graft implantation for the coronary artery bypass grafting (CABG). In spite of the favourable long-term results of this approach, the sensitivity of RA to vasoconstriction and spasm is still limiting its use. It has been suggested that vasospastic properties of the artery may differ depending on the location (proximal or distal). AIM: To compare the vasoreactive properties of proximal and distal sections of RA grafts. METHODS: Proximal and distal segments of RA were obtained from 27 patients undergoing CABG and isometric recordings of changes in smooth muscle force were performed mounted in the organ bath. Responses to cumulatively increasing concentrations of phenylephrine (PE), angiotensin II (AT-II), prostaglandin F2 (PGF2) and endothelin-3 (ET-3) were evaluated. RESULTS: Both proximal and distal segments of RA constricted in response to KCl, PE, AT-II, PGF2 and ET-3. Proximal segments demonstrate significantly greater spastic response to KCl, as well as to receptor-mediated agonists PE and more importantly vasoactive peptide AT-II. These differences remained statistically significant after correcting for vessel size and weight. In contrast, reactivity of both segments of RA to increasing cumulative doses of PGF2 and ET-3 was similar. CONCLUSION: Proximal segments of the radial artery are more susceptible to vasoconstriction induced by PE and AT-II, which should be taken into consideration in the clinical setting of CABG surgery. Increased muscle content in this segment does not fully explain this difference, which may result from varying receptor density and properties.