Background: Potential stresses associated with spaceflight include microgravity, acceleration and deceleration forces, a crowded environment and re-adaptation to normal gravity after landing.
Hypothesis: We hypothesized that spaceflight would result in histological changes in the adrenal glands of young rats.
Methods: Six week old male rats were group-housed in an Animal Enclosure Module (AEM) for a 17 d shuttle flight (STS-78). Ground-based controls included a baseline group, an AEM-housed group and a vivarium group. Adrenal glands were collected from 4-6 hours after flight, fixed, embedded in plastic and sections prepared for light microscopy.
Results: The adrenals from the baseline and vivarium groups had normal histological features. Some changes in the adrenal cortices from the ground-based AEM group included greater parenchymal cord-like formation. The adrenal weights and width of the zona fasciculata were greater in the flight group than the controls. There were also increased parenchymal cord-like formation with better demarcation of the vascular sinusoids in the zona reticularis and zona fasciculata, greater depletion of cytoplasmic lipid vacuoles, and an increased nuclear volume of the cells in the zona fasciculata when compared with the controls.
Conclusions: The adrenal changes in the ground-based AEM animals may be attributed to the confined space in the AEM. The adrenal enlargement and the histological changes observed in the flight animals may be attributed to spaceflight and possibly re-entry in addition to possible confinement stress in the AEM.