To study factors which modulate the tone of internal mammary artery (IMA) bypass grafts, right and left canine IMAs were studied in vitro in organ chambers: 1) increasing concentrations of the platelet-derived products adenosine diphosphate (ADP) or serotonin (5-HT) induced vasodilation of contracted right and left IMAs. The vasodilation caused by ADP was endothelium-dependent while serotonin acted directly on the vascular smooth muscle; 2) the autacoids histamine and bradykinin also induced IMA vasodilation, histamine via a direct action on the smooth muscle, and bradykinin through the release of nitric oxide; 3) in canine IMAs, the calcium ionophore A23187, which acts independently of receptors produced endothelium-dependent vasodilation of contracted blood vessels; 4) dopamine, dobutamine, and papaverine induced vasodilation of the IMA, regardless of the presence or absence of an intact intima; 5) norepinephrine induced profound IMA vasoconstriction which was comparable to contraction to potassium ions or the constrictor peptide endothelin; 6) in 83% of 20 biological assays the basal release of nitric oxide was bigger in left IMAs than right IMAs; 7) biological assays of IMAs confirmed the importance of prostacyclin (PGI2) in response to hypoxia; 8) no differences between right and left IMAs were observed studying the different drugs.
Mammary arteries; Endothelium, vascular; Neurotransmitters; Autacoids; Anoxia; Nitric oxide; Epoprostenol; Biological assay
