Hypertension increases the contractions to sumatriptan in the human internal mammary artery

The internal mammary artery is the graft of choice for myocardial revascularization. The tendency to spasm increases toward the distal end of the internal mammary artery, which is the portion generally used for anastomosis. The distal internal mammary artery is more pharmacologically responsive to 5-hydroxytryptamine and several other vasoconstrictor agents than its midsection.

We examined the effects of 5-hydroxytryptamine and a 5-hydroxytryptamine1-like receptor agonist sumatriptan on internal mammary artery segments (length, 3-4 mm) obtained from patients undergoing coronary artery bypass grafting. To unmask a 5-hydroxytryptamine1-like receptor-mediated contractile response, threshold concentrations of potassium chloride were used.

5-Hydroxytryptamine induced concentration-dependent contractions in all, quiescent and potassium chloride precontracted, preparations. Sumatriptan induced marked contraction in some of the quiescent internal mammary artery rings, whereas it elicited marked and concentration-dependent contractions in all of the preparations given a moderate tone by a threshold concentration of potassium chloride. The sensitivity to sumatriptan was higher in potassium chloride-precontracted distal arteries than it was for the quiescent distal segments. Additionally, the sensitivity to and the efficacy of sumatriptan were much more markedly potentiated by precontraction in the preparations taken from hypertensive patients.

The more marked potentiation of the responses in arteries from hypertensive patients may be one of the factors influencing the patency rates.