MECHANISM OF ACTION Antenatal corticosteroid therapy leads to architectural and biochemical changes that improve both lung mechanics (maximal lung volume, compliance) and gas exchange. These changes are primarily the result of accelerated morphologic development of type 1 and type 2 pneumocytes . Type 1 pneumocytes are responsible for gas exchange in the alveoli, while type 2 pneumocytes are responsible for production and secretion of surfactant (figure 1). Antenatal corticosteroids also alter production of surfactant binding proteins and enhance fetal lung antioxidant enzymes. For these changes to occur, however, the lungs need to have reached a stage of development that is biologically responsive to corticosteroids The biologic rationale for repeating antenatal corticosteroid therapy is based upon the observation that biochemical stimulation of surfactant production appears to be reversible in cell culture models (eg, surfactant protein mRNA levels decline to control levels after cortisol is removed) . However, other beneficial effects, such as cytostructural maturation, persist (in rhesus monkeys) after steroid exposure is withdraw
Posted on: Mon, 04 Nov 2013 22:46:59 +0000
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