EFFECT OF PRENATAL STEROIDS ON SKIN SURFACE HYDROPHOBICITY IN THE PREMATURE RAT

The skin surface of the newborn rat at term is highly hydrophobic. Thi s surface hydrophobicity plays a putative role in the transition from an aqueous to a gaseous environment at birth and is dependent on the p resence of an intact periderm. Glucocorticoids given to pregnant dams, during late gestation, will accelerate formation of the stratum corne um and reduce transepidermal water loss in prematurely delivered pups. We tested the related hypotheses that surface hydrophobicity and matu ration of the periderm are developmentally accelerated by prenatal exp osure to steroids. Thirty pregnant Sprague-Dawley rats received either normal saline or 0.5 mg/kg betamethasone on d 17 of gestation. After cesarean delivery on d 18, 19, and 20, dorsal skin surface hydrophobic ity was quantified by direct surface electrical capacitance (SEC) meas urement. Initial skin surface hydration at birth was significantly low er in steroid-treated pups than in control pups at gestational ages 19 and 20 d (3060 +/- 1379 versus 4441 +/- 153 pF and 646 +/- 295 versus 1493 +/- 1019 pF, respectively, p < 0.001, mean +/- SD). Likewise, af ter desorption of amniotic fluid, baseline skin hydration was signific antly lower in steroid-treated pups than in control pups at gestationa l ages 19 and 20 d (1862 +/- 1560 pF versus 4278 +/- 97 pF and 60 +/- 56 pF versus 128 +/- 264 pF, p < 0.001). Scanning and transmission ele ctron microscopy showed morphologic maturation of the periderm after s teroid treatment. These results demonstrate accelerated development of both functional and structural correlates of skin surface hydrophobic ity in the premature rat after prenatal exposure to steroids.