On the calibre of the ureteric lumen.

The cross sectional appearances of the lumen of rat ureter were compared in specimens fixed by perfusion and by immersion and processed for electron microscopy. After efficient perfusion fixation in untreated animals, and in animals previously injected with 6-hydroxydopamine, there was substantial dilatation of the ureter, and the lumen was approximately circular in section. In inadequately perfused and immersion-fixed material the lumen was usually narrowed, and was either slit-like or stellate in appearance. Ultrastructural examination indicated that closure of the lumen was accompanied by the development in the cells of the muscle coat of the features usually associated with contraction, and the possibility that the appearance of the ureter in well perfused specimens approximated to its state in vivo was discussed.