Neurogenic vasoreactivity of human internal thoracic artery is unaffected by endothelial cell integrity

Background The role of interval thoracic artery (ITA) nervous supply has no t been previously considered as a potential factor influencing excellent lo ng-term patency of an ITA graft. To define the interaction between the prim ary afferent neurons and endothelial cells of ITA, we investigated the effe cts of acute capsaicin administration in vitro on the isometric tension of human ITAs. Methods. Vessels were obtained from patients undergoing coronary bypass or from multi-organ transplant donors. Thirty-three ITA segments (5 mm wide) w ere suspended as rings between two stainless-steel stirrups in water-jacket ed (37 degrees C) tissue baths. The tissue baths contained 10 ml physiologi cal salt solution (PSS) of the following composition (mM/L): NaCl 119, KCl 4.7, NaH2PO4 1.0, MgCl2 0.5, CaCl2 2.5, NaHCO3 25, and glucose 11, aerated continuously with 95% O-2 and 5% CO2. Peptidase inhibitors, phosphoramidon (1 mu M) and captopril (1 mu M), were added to PSS to decrease peptide degr adation. Mechanical responses were measured isometrically and recorded on a polygraph via isometric force transducers, Vessels were preconstricted wit h submaximal concentrations of norepinephrine, After the tension had stabil ized, capsaicin was added cumulatively to the tissue bath. The viability of ITA was verified by its responses to endothelial-dependent (acetylcholine, 1 mu M) (n=20) and endothelial-independent (sodium nitroprusside, 10 mu M) (n=13) vasodilators. Results. The exposure of capsaicin (3 mu M) to human ITA produced varied ef fects on ITA irrespective of its endothelium, Capsaicin induced contraction of the ITA smooth muscle in 13 endothelium-intact ITA segments while it pr oduced vasoconstriction in 9 endothelium-denuded ITAs (p=0.6437). In respon se to capsaicin, relaxation of ITA smooth muscle was observed in 7 ITA ring s with endothelium, while vasodilation was present in 4 ITA segments withou t endothelium (p=0.4099). Conclusions, Capsaicin-sensitive neurons encircling human ITA produce a neu rogenic vasoreactive response independent of ITA endothelial cell integrity .