Fig. 3. Chemical structure of selected nitrovasodilators. GTN = Glyceryl trinitrate; ISDN = isosorbide dinitrate; IS-5-MN = isosorbide 5-mononitrate; NTP = nitroprusside [9].

action of NTG. By contrast, NO can dilate all arteriolar sizes [11]. This differential effect of NTG on arterioles of different sizes may play an important role in how NTG relieves angina pectoris. Because the small resistance vessels are not responsive to NTG, the resistance to flow in unobstructed coronary arteries is little changed. But the effect of NTG on flow in stenosed vessels is enhanced by its effect on the larger arterioles and on the epicardial stenoses themselves. This combination acts to reduce or eliminate any 'coronary steal' from affected to unaffected arteries. Such an advantage is not available from the non-organic nitrates.

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