HYPERTENSION INCREASES THE CONTRACTIONS TO SUMATRIPTAN IN THE HUMAN INTERNAL MAMMARY ARTERY

Background. The internal mammary artery is the graft of choice for myo cardial revascularization. The tendency to spasm increases toward the distal end of the internal mammary artery, which is the portion genera lly used for anastomosis. The distal internal mammary artery is more p harmacologically responsive to S-hydroxytryptamine and several other v asoconstrictor agents than its midsection. Methods. We examined the ef fects of 5-hydroxytryptamine and a 5-hydroxytryptamine(1)-like recepto r agonist sumatriptan on internal mammary artery segments (length, 3-4 mm) obtained from patients undergoing coronary artery bypass grafting . To unmask a 5-hydroxytryptamine(1)-like receptor-mediated contractil e response, threshold concentrations of potassium chloride were used. Results. 5-Hydroxytryptamine induced concentration-dependent contracti ons in all, quiescent and potassium chloride precontracted, preparatio ns. Sumatriptan induced marked contraction in some of the quiescent in ternal mammary artery rings, whereas it elicited marked and concentrat ion-dependent contractions in all of the preparations given a moderate tone by a threshold concentration of potassium chloride. The sensitiv ity to sumatriptan was higher in potassium chloride-precontracted dist al arteries than it was for the quiescent distal segments. Additionall y, the sensitivity to and the efficacy of sumatriptan were much more m arkedly potentiated by precontraction in the preparations taken from h ypertensive patients. Conclusions. The more marked potentiation of the responses in arteries from hypertensive patients may be one of the fa ctors influencing the patency rates.