Comparison of the Inhibitory Effects of Nifedipine, Nitroglycerin, and Nitroprusside Sodium on Different Types of Activation in Canine Coronary Arteries, with Comparative Studies in Human Coronary Arteries
The mechanical activity of helical strips from canine coronary arteries was recorded. Vessels from normal hearts and from hearts with a collateral circulation after experimental occlusion were investigated. Two types of activation were studied: (a) activation induced by noradrenaline, 10-5M, after blockade of β-adrenoceptors with propranolol (NA activation) and (b) activation induced by application of tetraethylammonium (TEA), 10-2M, after blockade of endogenous prostaglandin synthesis by indomethacin, 2 × 10-6M (TEA activation). TEA activation was more sensitive to nifedipine (ED50, 2 × 10-8M) than to nitroglycerin (ED50, 10-7M) or nitroprusside sodium (ED50, 3 × 10-7M). NA activation, on the other hand, was more sensitive to nitroglycerin (ED50, 10-8M) or nitroprusside sodium (ED50, 2 × 10-8M) than to nifedipine (ED50, 6 × 10-8M). In comparative studies with human coronary arteries excised postmortem, spontaneous rhythmic activity was often observed. This phasic activity was, as in TEA activation of canine coronary arteries, more sensitive to fedipine than to nitroglycerin. The differences between human and canine coronary smooth muscle are discussed.