CENTRAL CARDIOVASCULAR SHUNTS IN THE PERINATAL MARSUPIAL

Background. Marsupials are born at an early stage of development after a short period of gestation. In this study the nature and timing of c losure of the central cardiovascular shunts was investigated. Methods. Light and scanning electron microscopy were used to determine changes in central cardiovascular shunts in eight marsupial species with gest ation periods of between 12.5 and 36.5 days and birth weights ranging from 12.5 mg to 740 mg. Laboratory mice with a birth weight of about 1 ,000 mg and a gestation period of 21 days were included for comparison . Results. Marsupials have a ductus arteriosus and an interatrial comm unication. The former closes rapidly after birth in the marsupial; how ever the interatrial communication is in the form of a fenestrated sep tum, which closes as a result of tissue proliferation over a period of days after birth. An additional central shunt, an interventricular fo ramen, was found to persist in three species for a short time after bi rth. In one species, the eastern native cat, Dasyurus viverrinus, whic h has a gestation period of about 19 days and low birth weight of abou t 12.5 mg, in addition to the two common shunts there was a large inte rventricular communication and septation of the outflow tract was inco mplete. Conclusion. In adapting from intra-uterine life, it seems that marsupials have adopted different, but equally effective strategies, with regard to the circulatory system. (C) 1995 Wiley-Liss, Inc.