ACCELERATION OF BARRIER ONTOGENY IN-VITRO THROUGH AIR EXPOSURE

Immaturity of the epidermal barrier in the preterm infant may have ser ious clinical consequences. However, regardless of the degree of prema turity, the barrier rapidly matures such that by 2 wk all infants disp lay a competent barrier. To determine whether the change from an aqueo us (intrauterine) to a xeric environment might be the stimulus for thi s accelerated maturation, we examined the effects of air exposure on c utaneous barrier formation in vitro. Skin explants from d 17 fetal rat s were incubated either submerged or at the air-medium interface. As p reviously reported, a competent barrier formed under submerged conditi ons after 3-4 d, precisely mirroring the time course of maturation in utero. In contrast, barrier maturation was accelerated in air-exposed explants, with functional, histologic, and structural markers of barri er formation observed after only 2 d of incubation. A water-impermeabl e membrane blocked the acceleration of barrier formation, resulting in a developmental time course comparable to that for submerged explants . In contrast, a water vapor-permeable membrane did not block the acce leration. Glucocorticoids and thyroid hormone, which accelerate barrie r formation in utero or in vitro under submerged conditions, did not f urther accelerate barrier formation in the air-exposed model. These da ta indicate that: I) air exposure accelerates barrier ontogenesis, sug gesting that water flux may be an important signal for the accelerated barrier formation that occurs in premature infants; and 2) factors wh ich accelerate barrier formation in utero may not further accelerate b arrier formation in neonates.