Pulmonary venous sphincters in cattle

Abstract

The veins of cattle are unlike the rat because the focal venous smooth muscle protrudes deeply into the venous lumen and may completely obstruct perfusion. If the focal venous muscle has no innervation (this study) and can constrict without blood flow (as shown previously), then the venous constriction and, hence, local blood flow regulation must be controlled by local mediators.