Reactivity of human isolated internal mammary artery to constrictor and dilator agents. Implications for treatment of internal mammary artery spasm.

Perioperative spasm of the internal mammary artery (IMA) may occur after coronary artery bypass surgery. To establish the most appropriate dilator agent, we tested the reactivity of ring segments of human IMA in organ baths to various constrictor and dilator agents. We found that the thromboxane mimetic U46619 was the most potent IMA constrictor agent, followed by norepinephrine, serotonin, phenylephrine, and potassium chloride (K+). In K+- or U46619-precontracted IMA, glyceryl trinitrate and papaverine caused full relaxation. In K+-precontracted arteries, nifedipine, verapamil, and diltiazem caused full relaxation, but nifedipine was 15-fold more potent than the other calcium antagonists. In contrast, pretreatment of vessels with glyceryl trinitrate failed to alter subsequent contraction to U46619 or K+ while nifedipine pretreatment abolished subsequent contraction to K+ and reduced sensitivity of the IMA to U46619. We conclude that perioperative IMA spasm could be treated with the rapid-onset, nonspecific, vasodilator glyceryl trinitrate, but for prophylaxis of IMA spasm, calcium antagonists or specific receptor antagonists should be tested in the clinical setting.