Effect of Drugs on Myocardial Microcirculation

Abstract

Regarding the clinical and pharmacologic effects of two coronary vasodilator drugs, nitroglycerin and dipyridamole, an interesting paradox can be noted. On the one hand, nitroglycerin is widely used nowadays in the treatment of patients with coronary artery disease. However, the extent to which it relieves anginal pain by its effects on the coronary as opposed to the systemic circulation is unclear. Following sublingual or intravenous administration of nitroglycerin, an increase in myocardial blood flow was occasionally observed (Brachfeld et al., 1959, Luebs et al., 1966). In most studies, however, only minor and irregular changes (Eckstein et al., 1951, Sarnoff et al., 1958) or a decrease in total coronary flow occurred (Bernstein et al., 1966, Lichtlen, 1975, Rudolph et al., 1975). In the majority of clinical and experimental studies, intracoronary injection of nitroglycerin caused a slight increase in myocardial blood flow (Bernstein et al., 1966, Eckstein et al., 1951, Rudolph et al., 1975). On the other hand, dipyridamole as a potent coronary vasodilator is known to enhance total coronary flow by 360%–400% (Bretschneider et al., 1959, Elliott, 1961, Bretschneider, 1963, De Graff and Lyon, 1963, Fam and McGregor, 1968), but this drug does not relieve angina pectoris. The increase in total coronary flow could be due to a rise in blood flow velocity in individual capillaries, or due to a recruitment of myocardial capillaries previously not perfused.