Effects of acute administration of isoproterenol on the systemic and regional blood flow in the dog

The effects of isoproterenol on cardiac output and the blood flow to various parts of the body have been investigated in pentobarbital-anaesthetized dogs, by the microsphere method. Arterial and venous catheterizations were performed for haemodynamic measurements, drug infusions and blood samples. After a stabilization period, control measurements were carried out on the cardiac output, heart rate, blood pressure, expiratory minute volume and blood gases. Radioactive microspheres of 50 μm diameter, labelled with either ⁸⁵Sr or ¹⁴¹Ce, were then injected into the left ventricle. Thereafter the intravenous infusion of isoproterenol (0.5 μg min^?1 kg^?1 was started. Fifteen minutes after initiation of the drug infusion, the same parameters as in the control period were measured and the injection of radioactive microspheres into the left ventricle was repeated. At the end of the experiment, various organs and tissues were removed and weighed and their radioactivity was determined. The fractional distribution of cardiac output and the blood flow to various organs and tissues were calculated by the method after Rudolph &; Heymann (1967). The infusion of isoproterenol resulted in an increase of 57% in cardiac output but changes in regional blood flow varied. The fraction of cardiac output to the myocardium, skeletal muscle and skin were increased, whereas that to the kidney, pancreas and brain decreased. The fraction to the bronchial arteries and splanchnic organs except for the pancreas remained unchanged. The uneven distribution of cardiac output to the various areas may be due mainly to the differences in direct and indirect responses of individual vascular beds to isoproterenol.