Ontogeny of the pulmonary surfactant and antioxidant enzyme systems in the viviparous lizard, Tiliqua rugosa.

Abstract

The antioxidant enzyme (AOE) system protects the lung from oxidative damage. The pulmonary surfactant (PS) system lowers the interfacial pressure within the lung, improving lung compliance and aiding lung clearance. In mammals, the AOE and PS systems develop in tandem during the final 10%-20% of gestation. Here, we investigated the development of these systems in the viviparous skink, Tiliqua rugosa. The content of total phospholipid (PL), disaturated phospholipid (DSP), and cholesterol (Chol) increased in lung washings from foetal lizards with advancing gestational age. Similarly, the relative saturation of the PLs increased throughout gestation, with mid-stage 40 foetuses having a DSP/PL equivalent to newborns and adults. Maternal lizards had significantly less total PL, DSP, and Chol than nongravid and newborn lizards; however, the relative composition did not differ from nongravid animals. This presumably results from compression of the lungs under the bulk of the developing foetus. The Chol/PL and Chol/DSP ratios declined early in development such that mid-stage 40 embryos had comparable ratios to both newborns and adults. Thus, it appears that the PS system matures in a similar manner in skinks and in mammals. However, the composition of surfactant is complete some weeks before parturition, probably to enable improved survivorship of the precocial young in the event of premature birth. Unlike the surfactant lipids, the AOEs, catalase, superoxide dismutase, and glutathione peroxidase did not differ appreciably throughout gestation. It appears therefore that like the surfactant lipids the AOE system is in readiness for air breathing throughout the latter stages of gestation, possibly in preparation for premature birth. Unlike mammals, the PS and AOE systems develop independently from one another.