VASOCONSTRICTOR PROFILE OF THE INFERIOR EPIGASTRIC ARTERY

The inferior epigastric artery is a putative arterial bypass graft. The receptor mechanisms that control vascular tone are thought to play a role in the performance of bypass conduits. We have compared the vascular reactivity of the inferior epigastric artery with that of the internal mammary artery. Segments from a total of 15 inferior epigastric and 12 internal mammary arteries were examined for their response to increasing concentrations of noradrenaline, 5-hydroxytryptamine, dopamine, histamine, endothelin-1, or the thromboxane analogue U46619. The responsiveness of the smooth muscle was significantly greater in the inferior epigastric artery (p < 0.05) as judged by contractions elicited by 90 mmol/L potassium chloride. However, although the response of the inferior epigastric artery tended to be greater, this significant enhancement of smooth muscle function was not paralleled by the maximal responses of noradrenaline, 5-hydroxytryptamine, dopamine, histamine, or endothelin-1. However, the tension generated in response to U46619 did differ significantly, with maximal responses in the inferior epigastric and internal mammary arteries of 59.2 +/- 8.3 mN and 35.0 +/- 3.6 mN, respectively. When receptor function was compared by expressing the response as a percentage of that of 90 mmol/L potassium chloride, it was revealed that noradrenaline was capable of inducing significantly greater relative contractions in the internal mammary artery (114.8% +/- 20.5%) as compared with the inferior epigastric artery (49.9% +/- 19.1%); the potency of this constrictor was sixfold greater in the internal mammary artery. There were no significant differences in efficacy when comparing responses to 5-hydroxytryptamine, dopamine, histamine, endothelin-1, and U46619, but a fourfold change in potency for 5-hydroxytryptamine in the inferior epigastric artery was observed (p < 0.05). We conclude that the inferior epigastric artery possesses a specific receptor-mediated vasoconstrictor profile, which may influence its performance as a bypass graft. This profile bears similarities and differences to that observed in established arterial bypass graft conduits.