Internal Mammary Artery Rings Research Articles

Different interactions of platelets with arterial and venous coronary bypass vessels

We studied the interaction of platelets with the wall of human internal mammary arteries and saphenous veins, suspended in organ chambers for measurement of isometric tension. Vessels were obtained during coronary bypass surgery and cut into 5 mm rings; in some the endothelium was chemically removed. Rings from several patients were randomly chosen for each experiment, and in each ring six concentrations of platelets (from healthy blood donors; 1-75 × 10 3/μl) were tested consecutively and concentration-response curves constructed; the areas under these curves were used for statistical comparisons. In rings of internal mammary artery contracted in response to noradrenaline, aggregating platelets induced endothelium-dependent relaxation which was prevented by apyrase (0·67 U/ml ADPase activity) and L-N G-monomethylarginine (1 mmol/l). By contrast, in saphenous vein rings contracted in response to noradrenaline, aggregating platelets induced only a further increase in tension. In quiescent vessels, the platelet-induced contraction did not occur in arteries with endothelium but that in veins was greater and facilitated by endothelium. Preincubation of platelets with aspirin (10 μmol/l) reduced the contraction in both vessels, but contraction was abolished only in the presence of both the thromboxane receptor antagonist SQ-30741 and the serotoninergic (5HT 2) receptor antagonist ketanserin. These findings show that platelet-derived ADP causes release of nitric oxide by the endothelium of internal mammary artery but not of saphenous vein; thromboxane A 2 and serotonin mediate contraction in vein but not artery with endothelium. These differences may contribute to differences in graft function and the clinical efficacy of antiplatelet drugs.

Relaxation of human internal mammary artery rings by neutrophils: Evidence for generation of an EDRF-like compound

Relaxation of human internal mammary artery rings by neutrophils: Evidence for generation of an EDRF-like compound

Vasorelaxant effects of atriopeptins in human internal mammary artery

The vasorelaxant effects of the atriopeptins, AP-(103–126) and AP-(103–123) were compared in human internal mammary artery (IMA) rings which had been contracted with norepinephrine. AP-(103–126) completely relaxed the IMA with an IC 50 within the physiologically relevant range (15 nM). However, relaxation with AP-(103–123) was greatly reduced compared to AP-(103–126), with complete relaxation observed in only half of the vessels tested and only at concentrations of 10–50 μM. These results indicate that the atriopeptin (AP) receptor in human arteries may be more similar to the AP receptor in rabbit rather than rat arteries.