Fig. 2

Localization of [³H]FK506 binding along the path of sperm maturation. [³H]FK506 autoradiography was performed on 20-µm fresh frozen sections of rat caput and cauda epidydimides and vas deferens. (A) In the caput or head of the epididymis, there is selective labeling of the principal cells that line the tubular lumen. (B) In the cauda, there is exclusive labeling of the tubular lumen, where the sperm are located. (C) In the vas deferens, there is intense labeling of the lumen, with lower levels present in the lining epithelium. The layers of smooth muscle in the wall of the vas deferens are completely negative.