BRONCHIAL CIRCULATION IN THE MARSUPIAL OPOSSUM, DIDELPHIS-MARSUPIALIS

This study characterizes the existence of a bronchial circulation in a marsupial, an animal which does not undergo placental development and does not have a ductus arteriosus. Direct perfusion of the lung by th e pulmonary vasculature during the fetal development of opossums may o ccur, potentially eliminating the need for a bronchial circulation. We used radio- and fluorescent-labeled microspheres in conjunction with postmortem intravascular casting to determine if opossums have a syste mic (bronchial) blood supply to the lung (n = 9). Gross postmortem exa mination of the intravascular casts showed a well-developed common bro nchial artery. The histological distribution pattern of fluorescent mi crospheres was primarily to the airways. A few fluorescent microsphere s were observed in the alveolar capillaries, indicating that a precapi llary bronchial-to-pulmonary anastomosis exists in the opossum. Using the reference flow technique, total bronchial blood flow to the left l ung averaged 0.95 +/- 0.58 SE ml/min. The presence of a bronchial circ ulation in the opossum suggests that it is more than a vestigial struc ture from embryonic development, potentially supporting its functional importance for carrying nutrients to the airway.