Analysis of vasodilated effect of nitroglycerin on microvessels

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We examined the effect of nitroglycerin (NTG) on the diameter and diastolic-to-systolic pulsation amplitude of large (ID>100mum) and small (ID<100mum) subendocardial arterioles with their segmental responses. In 10 open-chest, anesthetized pigs, subendocardail arterioles of beating hearts (n=18) were videorecorded using a needle-probe videomicroscope. Subendocardial arteriolar diameter was determined before and 1-2 min after NTG administration (25mum/kg iv). In an additional experiment using three pigs, we monitored the transient response of subendocardial small arterioles (n=5) from the time before NTG administration until 3 min after NTG.NTG dilated large subendocardial arterioles by 13(]SY.+-。[)4% (mean(]SY.+-。[)SD,n=10, p<0.01) at about 1.5 min after NTG,but not small subendocardial arterioles (2(]SY.+-。[)2%, n=8, not significant). However, the small arterioles responded transiently to NTG in an earlier phase, especially to higher dose. The percent diameter change of large subendocardial arterioles between diastole and systole at 1.5 min after NTG administration was 32(]SY.+-。[)4%, which was larger than that under control conditions (19(]SY.+-。[)8%, p<0.05). The pulsation amplitude of small subendocardial arterioles at this time was almost unchanged by NTG (16(]SY.+-。[)8 vs.17(]SY.+-。[)6%, NS) but increased transiently in an earlier phase. In conclusion , NTG dilated large subendocardial arterioles on the plateau phase of its impulse (intravenously) response (-1.5 min after NTG). It dilated small arterioles transiently at -15 s, but not at 1.5 min. NTG enhanced the diastolic-to-systolic pulsation amplitude of large subendocdardial arteop ; es at 1.5 min and transiently of small arterioles.