The effect of ambient temperature on papaverine-induced relaxations in canine saphenous veins

This study was designed to measure the effect of ambient temperature (25° C) on papaverine-induced relaxations in canine saphenous veins. Segments of vein were suspended in water-jacketed tissue baths at 37° C, and isometric tension was recorded. After equilibration, veins were preconstricted by a median effective dose of norepinephrine 2 x 10-6mol/L at either 25° C or 37° C. Consequent dose-dependent relaxations showed that papaverine (10-7 to 10-3mol/L was three times more potent as a dilator at 37° C than at 25° C, with half-maximal relaxations occurring at 2.2 × 10-5mol/L and 6.4 x 10-5mol/L, respectively. A 10-4 mol/L dose of papaverine completely relaxed veins at 37° C, whereas veins at 25° C never fully relaxed even at ten times the standard concentration. In addition, the time for half-maximal relaxation with a 10-4mol/L dose of papaverine averaged 40 minutes at 25° C compared with 22 minutes at 37° C; this is indicative of a reduced relaxation rate at the lower temperature. These data show that papaverine is a slower and less potent dilator of canine saphenous veins at 25° C than at 37° C. This may have implications for the use of papaverine in the operating room, where it is usually applied at ambient temperature to reduce vasospasm of the saphenous vein during coronary artery bypass procedures. (J Thorac Cardiovasc Surg 1992;104:1289-93)