Nitroglycerin induced 90% relaxation in large porcine coronary microvessels compared to only 20% in small microvessels, indicating diminished biotransformation in smaller resistance vessels.
Absolute Event Rate: 90% vs 20%
The responses of small (60-100 microns), medium (101-190 microns), and large (191-300 microns) porcine coronary microvessels to nitroglycerin were examined in vitro using a video-imaging apparatus. Large coronary microvessels, preconstricted with acetylcholine, relaxed by 90% in response to nitroglycerin, whereas small microvessels relaxed only 20% to nitroglycerin. Responses to putative metabolites of nitroglycerin, S-nitrosocysteine, and nitric oxide, were also examined. S-Nitrosocysteine produced equal relaxations in all sizes of coronary microvessels. Nitric oxide was 10 times more potent in large coronary arteries than in small but produced greater than 90% relaxation of all sizes of coronary microvessels at the highest concentrations. Bradykinin and the calcium ionophore A23187, which release endothelium-derived relaxing factor (EDRF), produced similar relaxation in small, medium, and large microvessels. The compound LY 83583 (which depletes vascular guanylate cyclase) reduced responses to nitroglycerin, nitric oxide, S-nitrosocysteine, bradykinin, and the calcium ionophore A23187 in microvessels of all sizes. Our data are compatible with the concept that nitroglycerin must undergo reductive processing to exert its vasodilator effect, likely through the formation of nitrosothiols. In small coronary microvessels, this biotransformation of nitroglycerin is diminished compared with larger coronary arteries. This may be caused by a relative deficiency of available sulfhydryl groups or a lack of enzymes necessary for conversion of nitroglycerin to its active metabolites in small coronary resistance vessels.
Sellke et al. (Thu,) conducted a other in Porcine coronary microvessels. Nitroglycerin vs. Different vessel sizes (small vs large) was evaluated on Relaxation response to nitroglycerin. Nitroglycerin induced 90% relaxation in large porcine coronary microvessels compared to only 20% in small microvessels, indicating diminished biotransformation in smaller resistance vessels.