Respiratory function in a newborn marsupial with skin gas exchange.

The Julia Creek dunnart (Sminthopsis douglasi) is a marsupial born after approximately 12 days of gestation. At birth, the newborn is approximately 4 mm long and weighs approximately 15 mg. Gaseous metabolism (oxygen consumption rate, V(O2), rate of carbon dioxide production, V(CO2) was measured separately across the airways (lungs) and the rest of the body (skin). At pouch temperature (36 degrees C) total V(O2) (i.e. skin + lungs) averaged 15 +/- 2 S.E.M. ml x kg(-1) x min(-1). At birth the skin contributed almost the total gaseous metabolism, and at 3 weeks approximately 1/3 of the total. The compliance of the respiratory system, per unit of body weight, was similar to that of other newborn mammals. During the first postnatal days breathing was an occasional event determined by gross body movements. Artificial expansion of the lungs temporarily stopped breathing, presumably a manifestation of the Hering-Breuer reflex. By the 2nd-3rd week breathing was regular, pulmonary ventilation (V(E)) averaged 263 ml x kg(-1) x min(-1), tidal volume (V(T)) 3.4 ml x kg(-1), breathing frequency (f) 87 breaths x min(-1). Lowering ambient temperature in steps from 36 to 20 degrees C reduced both lung and skin gaseous metabolism. V(E) and f, at first, were little affected but eventually they dropped in approximate proportion to metabolism, whereas V(T) remained unchanged. In conclusion, for the newborn dunnart gas exchange through the skin is a requirement because of the inefficient V(E). To what extent the V(E) adjustments to changes in metabolic rate reflect mechanisms of regulation remains unresolved.