Unique Regional Distribution of E 43. Ketosteroid-5a-Ox idoreductase and Associated Epididymal Morphology in the Marsupial, Dideiphis Virginiana

The epididymal epithelial ultrastructure has been described in the adult male North American opossum, Dideiphis virginiana. Morphological results have suggested that absorptive activity is prominent in the proximal epididymal region by virtue of numerous microvilli, an endocytotic complex, dense granules, and multivesicular bodies in the apical cytoplasm. In contrast, the middle and distal epididymal regions exhibit ultrastructural features indicative of protein synthesis such as large invaginated euchromatic nuclei, large nucleoli, and in-creased amounts of granular endoplasmic reticulum. It is in the middle and distal epididymal regions where sperm head rotation and sperm pairing take place. Epididymal L-3-ketosteroid-5ct-oxidoreductase (5cs-reductase) activity also has been measured. It has been found that the level of enzyme activity differs significantly (p<O.O1) between the proximal, middle, and distal epididymal regions. Enzyme-specific activity has been found to be highest in the middle region (47.6 ± 5.4 pico-moles 5cr-reduced androgens formed/h/mg protein), lower in the distal region (18.3 ± 0. 7 picomoles 5cr-reduced androgens formed/h/mg protein), with little activity (2.4 ± 1.2 picomoles 5cr-reduced androgens formed/h/mg protein) found in the proximal epididymal region. This regional distribution of enzyme activity differs markedly from that reported for eutherian mammals. Both the suggested epididymal protein synthetic and secretory activity and the level of epididymal 5cr-reductase activity appear to correlate regionally with the morphological changes that occur in the opossum spermatozoa as they transit the epididymis