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

BACKGROUND: The role of internal thoracic artery (ITA) nervous supply has not been previously considered as a potential factor influencing excellent long-term patency of an ITA graft. To define the interaction between the primary afferent neurons and endothelial cells of ITA, we investigated the effects 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) were suspended as rings between two stainless-steel stir-ups in water-jacketed (37 degrees C) tissue baths. The tissue baths contained 10 ml physiological 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% O2 and 5% CO2. Peptidase inhibitors, phosphoramidon (1 microM) and captopril (1 microM), were added to PSS to decrease peptide degradation. Mechanical responses were measured isometrically and recorded on a polygraph via isometric force transducers. Vessels were preconstricted with submaximal concentrations of norepinephrine. After the tension had stabilized, capsaicin was added cumulatively to the tissue bath. The viability of ITA was verified by its responses to endothelial-dependent (acetylcholine, 1 microM) (n=20) and endothelial-independent (sodium nitroprusside, 10 microM) (n=13) vasodilators. RESULTS: The exposure of capsaicin (3 microM) to human ITA produced varied effects on ITA irrespective of its endothelium. Capsaicin induced contraction of the ITA smooth muscle in 13 endothelium-intact ITA segments while it produced vasoconstriction in 9 endothelium-denuded ITAs (p=0.6437). In response to capsaicin, relaxation of ITA smooth muscle was observed in 7 ITA rings with endothelium, while vasodilation was present in 4 ITA segments without endothelium (p=0.4099). CONCLUSIONS: Capsaicin-sensitive neurons encircling human ITA produce a neurogenic vasoreactive response independent of ITA endothelial cell integrity.