In vitro comparison of glyceryl trinitrate-verapamil with other dilators of human saphenous vein

Background: A common problem encountered during harvesting of the saphenous vein for coronary artery bypass grafting (CABG) is spasm of the vein. The previous work of the present authors has led to the development of a dilator solution containing glyceryl trinitrate (GTN) and verapamil for use during harvesting of the saphenous vein (SV) and the internal mammary artery. The present organ bath study was designed (i) to determine the best vasodilator agents for the saphenous vein during harvesting and (ii) to investigate the presence of any synergistic effect when vasodilator agents are combined. Methods: Discarded segments of saphenous vein were collected from 46 patients undergoing CABG and studied in organ baths. Initially veins were contracted with potassium or thromboxane A(2) mimetic (U46619). Dilators were added individually or in com-bination in clinically relevant concentrations to study time of onset and maximum effect. The vasodilator agents tested included GTN, verapamil (V), sodium nitroprusside (SNP) and nicorandil (N). Results: When rapidity of onset (i.e. relaxation caused in the first minute) was considered, GTN or combinations containing GTN, caused a response that was significantly faster than the other vasodilators (P < 0.05). The maximum response caused by the GTN-V combination (61.4 +/- 9.6%) was significantly greater than all the other single dilators, SNP (35 +/- 4%) and N (10 +/- 3%) (P < 0.05). However, no synergistic effects were demonstrated. Conclusions: The present paper demonstrates the following conclusions: (i) glyceryl trinitrate is a rapidly acting dilator of the human isolated SV. (ii) GTN-V combination is a potent combination causing a maximum dilator effect that is significantly greater than single agents including SNP and N.