Exposure to high gravitational acceleration forces acting along the body axis from the head to the feet (+Gz) severely reduces blood fl ow to the visceral organs, including the kidneys. Extracellular signal-regulated kinase (ERK) fi gures predominantly in mediating kidney cell responses to a wide variety of stress-related stimuli. Th ough previous studies have shown the activation of ERK in some experimental models, the regulation of ERK associated with +Gz exposure has not yet been investigated. Th e aim of this study was to examine the eff ect of high +Gz exposure on ERK activation in the kidneys. Using a small animal centrifuge, eight male Sprague-Dawley rats were exposed to +10Gz or +13Gz three times for 3 minutes each. Th e bilateral kidneys were obtained from each rat, and the expression levels of phosphorylated ERK (p-ERK) were evaluated using immunohistochemistry. In the control group, the collecting duct epithelium displayed faint cytoplasmic staining with no nuclear staining of p-ERK. By contrast, rats exposed to +10Gz showed strong nuclear staining intensity for p-ERK. In the renal papilla, the epithelial cells of collecting ducts and thin segments of the loop of Henle exhibited strong nuclear immunoreactivity for p-ERK. Rats exposed to +13Gz also showed the same staining intensity and distribution of p-ERK expression as that of rats exposed to +10Gz. Th is study is the fi rst to describe +Gz exposure-induced alteration in the expression of p-ERK in the kidneys. Our fi nding suggests that high +Gz exposure leads to the activation of ERK in the renal papilla.
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