EFFECT OF TEMPERATURE ON GLYCERYL TRINITRATE INDUCED RELAXATION OF RABBIT AORTA

It has previously been shown that the vasodilatory response to glycery l trinitrate (GTN) was decreased during hypothermic cardiopulmonary by pass. The purpose of these experiments was to determine the effect of temperature on GTN-induced relaxation and on GTN biotransformation in rabbit aorta. It was determined that the EC(50) of GTN on rabbit aorti c rings (RARs) was increased significantly from 1.8 x 10(-8) M at 37 d egrees C to 3.4 x 10(-8) M at 27 degrees C (p < 0.05). The production of NO by rabbit aortic strips (RASs) was significantly less at 27 degr ees C compared with 37 degrees C after 80 min, being 9.62 x 10(-11) +/ - 13.2 x 10(-11) mol NO/g wet wt. RASs compared with 5.71 x 10(-10) +/ - 9.43 x 10(-11) mol NO/g wet wt. RASs, respectively (p < 0.05), after 80 min incubation. There was no difference in the amount of glyceryl- 1,2-dinitrate (1,2-GDN) produced from GTN at the two temperatures. The ED(20) for NO-induced relaxation of RARs increased from 3.46 x 10(-10 ) +/- 2.24 x 10(-10) mol at 37 degrees C to 1.01 x 10(-9) +/- 4.51 x 1 0(-10) mol at 27 degrees C (p < 0.05). These data indicate that the bi otransformation of GTN and the release of NO were impaired by hypother mia, and that this, as well as a decrease in the tissue response to NO at 27 degrees C, explains the decrease in GTN activity at reduced bod y temperatures.