Absence of arteriovenous anastomoses in anesthetized sheep

Microspheres, approximately 50 µ in diameter and labeled with scandium 46, were injected into the jugular vein in three sheep and into the left ventricle in one. Radioactivity was recovered only from the lungs after jugular injections. After left ventricular injection, the fraction of radioactivity recovered from the lungs corresponded closely to the proportion of cardiac output carried by the bronchial circulation. It appears that no physiologically significant arteriovenous anastomoses exist in sheep under the experimental condition.