Studies of the coronary microcirculation of the cat

Coronary capillary red cell velocity and capillary diameter were measured in the left atrium of the intact beating cat heart by transillumination of the left atrial muscle. Capillary red cell velocity was determined from moving pictures after injection of methacholine, nitroglycerin, norepinephrine, isoproterenol and after vagal stimulation. Coronary capillary red cell velocity declined with methacholine, vagal stimulation and nitroglycerin, and increased with norepinephrine and isoproterenol. There is evidence of autoregulation in the coronary bed after administration of nitroglycerin and isoproterenol. Temporary arrest of capillary flow was observed after injection of methacholine and vagal stimulation.