Expression of AQP9 in the rat efferent ductules. (A) In control rats AQP9 was expressed in the microvillus border of the non-ciliated cells in the epithelium. Ciliated cells (c) were negative for AQP9. (B) Castration caused an evident decrease in the AQP9 staining when compared to controls. (C) Treatment with corn-oil maintained the AQP9 staining at levels similar to castrated rats. Replacement with estradiol (D), DHT (E) and 3β-diol (F) recovered the epithelial AQP9 staining to control levels. Insert in A = negative control. Inserts in B-F = detail of ciliated cells negative for AQP9. Scale bar in A = 25 μm.