D. Kouretas et I. Taitzoglou, Dexamethasone has a biphasic effect on the c-Jun m-RNA expression in the fetal and adult rat lung, in vivo, CELL MOL B, 45(2), 1999, pp. 219-223
Glucocorticoids are a very potent therapy for the treatment of asthma as we
ll for lung maturation in the prematurely newborn animals and human. It has
been demonstrated that glucocorticoid receptors antagonize the actions of
inflammatory mediators through control of the specific DNA binding of the t
ranscriptions factors c-Jun and c-Fos, and also decrease the mRNA and prote
in levels of these two transcription factors in a number of in vivo and in
vitro studies. Additionally, glucocorticoids promote maturation of immature
lungs, thereby increasing the production of surfactant proteins which are
responsible for prevention of alveolar collapse. In the present study, the
expression of c-Jun and the influence of dexamethasone on mRNA levels of c-
Jun in different developmental stages in the rat lung, was examined. It was
found that dexamethasone stimulated c-Jun expression throughout late gesta
tional period, by similar to 50%. On day 16 postnatal, when developmental c
hanges in the newborn lung have not been completed, dexamethasone also incr
eased c-Jun expression by similar to 50%. Later, on postnatal day 35, when
lung maturation and development has been completed, dexamethasone treatment
resulted in lowered c-Jun expression, approximately 50%. During late fetal
life and until postnatal day 16, c-Jun expression was gradually increased,
indicating that c-Jun is needed to support lung development and normal fun
ction. On postnatal day 35, c-Jun mRNA levels showed a slight decrease. The
biphasic effect of dexamethasone on c-Jun expression during rat lung devel
opment is of interest. It is possible that c-Jun participates in rat lung d
evelopment through distinct mechanisms in different developmental stages.