In mammals, a terminally-differentiated epidermis forms the biological“spacesuit” interfacing the organism with a changing external environment. Both rats and humans develop a water-retentive epidermal barrierin utero during late gestation. Calcium (Ca) is a major regulator of this process. The effects of spaceflight and readaptation on epidermal development and skin calcium homeostasis are unknown. In this study, 10 pregnant Sprague-Dawley rats were maintained in orbit aboard the space shuttle Atlantis from gestational day 9 to day 20 (term = day 23). Epidermal, dermal and whole skin specimens were collected at recovery (day 20) and following re-adaptation to terrestrial gravity at the time of birth. Specimens were analyzed for: 1) total Ca by atomic absorption spectroscopy, 2) morphological differences by electron and light microscopy, and 3) barrier integrity by cyclic voltammetry and measurement of 3H2O flux. In fetal whole skin specimens, a significant increase in Ca was observed in the flight (F) group compared to synchronous (SC) and vivarium controls (VC) (mean ± sem; 7.7 ± 0.2* vs 6.5 ± 0.2 and 7.0 ± 0.1u g/Ca/100 mg wet weight, *p<0.05). Conversely, in postnatal epidermal samples, the F group demonstrated a significant decrease in Ca over both SC and VC groups (10.7 ± 0.4* vs 14.6± 0.8 and 14.3 ± 0.8, *p<0.05). There was no difference between any of the groups in dermal Ca. Histologically, there was an increase in the number of stratum corneum layers in the F group compared to the SC and VC groups (13.1 ± 0.4* vs 11.7 ± 0.3 and 12.0 ± 0.4, *p<0.05). After a 4 hour exposure to an applied electric current (100 uA), whole skin from the F group exhibited a significantly lower percent decrease in electrical resistance than either the SC or the VC groups indicating that the F group was less prone to damage (48.9 ± 7.8* vs 64.9 ± 9.1 and 58.8 ± 9.2, *p<0.05).

These results: 1) demonstrate that mammalian pregnancy can be sustained under conditions of microgravity, and 2) support the hypothesis that spaceflight and readaptation alter important barrier properties of the mammalian epidermis.