GLUCOCORTICOIDS ACCELERATE FETAL MATURATION OF THE EPIDERMAL PERMEABILITY BARRIER IN THE RAT

The cutaneous permeability barrier to systemic water loss is mediated by hydrophobic lipids forming membrane bilayers within the intercellul ar domains of the stratum corneum (SC). The barrier emerges during day 20 of gestation in the fetal rat and is correlated with increasing SC thickness and increasing SC lipid content, the appearance of well-for med lamellar bodies in the epidermis, and the presence of lamellar uni t structures throughout the SC. Because glucocorticoids accelerate lun g lamellar body and surfactant maturation in man and experimental anim als, these studies were undertaken to determine whether maternal gluco corticoid treatment accelerates maturation of the epidermal lamellar b ody secretory system. Maternal rats were injected with betamethasone o r saline (control) on days 16-18, and pups were delivered prematurely on day 19. Whereas control pups exhibited immature barriers to transep idermal water loss (8.16+/-0.52 mg/cm2 per h), glucocorticoid-treated pups exhibited competent barriers (0.74+/-0.14 mg/cm2 per h; P < 0.001 ). Glucocorticoid treatment also: (a) accelerated maturation of lamel lar body and SC membrane ultrastructure; (b) increased SC total lipid content twofold; and (c) increased cholesterol and polar ceramide cont ent three- to sixfold. Thus, glucocorticoids accelerate the functional , morphological, and lipid biochemical maturation of the permeability barrier in the fetal rat.