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Nephrectomized male rats were infused i.v. with [14C]-urea. The amount of radioactivity in subsequent micropuncture samples of cauda epididymal tubule (CET) fluids demonstrated a restricted movement of [14C]-urea into the CET. However, in the seminiferous tubules (SNT), radioactivity from [14C]-urea became higher than in blood plasma. 2, 4-dinitrophenol and ouabain inhibited this uphill movement of [14C]-urea thus giving evidence for active transport of urea into the rat SNT.
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Turner et al. (1979) studied this question.
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