Influence of the endothelium on the responses to endogenous agonists in human internal mammary and gastroepiploic arteries.

The higher patency rate of internal mammary artery grafts compared to venous grafts has been ascribed to its endothelial function, namely a greater capacity to release endothelium-derived relaxing factor and to inhibit serotonin-induced contractions. Gastroepiploic and mammary arteries were obtained intraoperatively from 27 patients and suspended in organ chambers to record isometric tension. The relaxations to acetylcholine were similar in both vessels. The contractions to serotonin, normalized as a per cent of KCl (90 mM)-induced contractions, were 46 +/- 15% for the internal mammary artery and 18 +/- 5% for the gastroepiploic artery. Endothelium removal equally potentiated the responses to serotonin: the maximal responses (% of KCl) increased to 63 +/- 18% and 41 +/- 6%, respectively. The contractions to endothelin were also higher in the internal mammary artery: 166 +/- 19% vs 102 +/- 6% of KCl (p < 0.05), but were not affected by endothelium removal. However, the capacity to contract, expressed in tension developed, was higher in the gastroepiploic artery: the KCl (90 mM)-induced contraction was 2.6 +/- 0.3 g in the internal mammary vs 7.9 +/- 0.9 g in the gastroepiploic artery (p < 0.001). Histologically, similar wall thickness and paucity of atherosclerotic lesions were observed, but the medium was mainly elastic in the internal mammary and muscular in the gastroepiploic artery. Thus, despite a similar endothelial function and greater responsiveness of the mammary artery to endogenous vasoconstrictors when compared to a receptor-independent vasoconstrictor, the higher contractile capacity of the gastroepiploic artery might be a disadvantage in terms of graft function and patency.