STUDIES ON REGIONAL FINE-STRUCTURE AND FUNCTION IN THE RABBIT EPIDIDYMIS

The regional fine structure of principal cells in the rabbit epididymal duct is described. Pinocytotic markers and enzyme cytochemistry were used to study pinocytotic mechanisms. Three main segments were defined. The initial segment showed selective micropinocytosis with transfer of surface membrane into large multivesicular bodies. The middle segment showed profuse pinocytosis of opaque material in the lumen and of the pinocytotic markers, and abundant lysosomes. The terminal segment showed some micropinocytosis only with small multivesicular bodies. Iron dextrin only was taken up. There was some evidence of micro-merocrine protein secretion in the initial segment, but most of the lumenal material was taken up again in the proximal part of the middle segment. Small vacuoles appeared to form from the Golgi complex in the other segments, too. These vacuoles may represent merocrine secretory vacuoles in all principal epididymal cells. Morphological sperm maturation is completed in the proximal half of the middle segment and functional maturation in the proximal third of the terminal segment.