Effects of nitrates in various vascular sections and regions.

Recently there has been much progress towards defining the action of nitrates, and related compounds, at a biochemical level. However, in vivo, differences in the effects of nitroglycerin (GTN) between specific sections of the vascular tree and various regions of the circulation are still not well understood. The actions of nitrates as they relate to the alleviation of myocardial ischemia are briefly reviewed. Then, an attempt is made to analyze separately the nitrodilator influences in the large and medium sized arteries, the venous system and the arterioles, in vivo. When pitfalls such as nonselectivity of indexes of drug action and secondary compensatory regulatory influences are considered, a surprising responsiveness of the resistance vessels to GTN is unmasked, revealing a remarkable uniformity in the profile of GTN action within different sections of the vascular tree. Nitrate effects in these vascular sections are then compared among several important regions of the circulation (i.e. mesenteric, skeletal muscle, brain etc.), and similarities or differences in action are noted. Finally the concepts presented here are related to some areas of controversy regarding nitrate action, in an attempt to form a basis for a better understanding of the sometimes confusing nitrate literature.