Ultrastructure of the Pelvic Epithelium of the rabbit Kidney and Its Morphological Changes in the Experimental Hydronephrosis / 대한비뇨기과학회지

ABSTRACT

The authors designed experiments to clarify ultrastructure of the renal pelvic epithelium and to observe its morphological changes in the postobstructed kidney by means of light, scanning and transmission electron microscopy. A total of 27 rabbits weighing about 2.5kg body weight, 3 for normal group and 24 for group of postobstruction, were used. Under pentothal sodium anesthesia, complete ureteral obstruction was accomplished by ligation on the left ureter 1cm above the ureterovesical junction. The experimental animals were sacrificed at 1st, 2nd, 3rd and 4th week after unilateral ureteral ligation. The kidneys for light microscopy were fixed in 10% neutral formalin, embedded in paraffin, sectioned at a thickness of 6 um and stained with hematoxylin and eosin. For scanning electron microscopy, tissue specimens taken from the renal papilla, peripelvic column, pelvic pouch and funnelshaped pelvic wall, were fixed in 1.5% paraformaldehyde-1% glutaraldehyde solution prior to fixation in 1% osmium tetroxide, dehydrated in alcohol, transferred to isoamyl acetate and dried in the critical point drier(Polaron E 3,000). Subsequently, specimens were coated with gold and observed by an electron microscope(JSM-35C). For transmission electron microscopy, pre-and post-fixed tissue blocks taken from various portions of the pelvic wall were embedded in Araldite. Ultrathin sections cut with an ultramicrotome(LKB-V) were contrasted with uranyl acetate and lead acitrate, and examined by an electron microscope(JEM-100B). The results were as follows The renal papilla and peripelvic column were lined with simple cuboidal or columnar epithelium which was composed of the principal cells with a few organelles and numerous short microvilli and the cells with a single cilium. The pelvic pouch was lined with pseudostratified columnar epithelium. The superficial cells were characterized by the presence of numerous secretory granules which were round or oval in shape(668+/-174nm) and showed various electron densities. The funnel-shaped portion of the pelvic wall was lined with transitional epithelium. The superficial cells containing a few fusiform vesicles were expanded in parallel with the luminal surface, and luminal plasma membrane of the cells showed well developed microridges and polygonal plaques consisting of asymmetric unit membrane. The following morphological changes were observed in different portions of the pelvic epithelium of the hydronephrotic kidney after ureteral obstruction. The cell organelles, such as granular endoplasmic reticulum, mitochondria and ribosomes, were obviously increased in the epithelial cells of the renal papilla and peripelvic column. In the superficial cells of the pelvic pouch, the secretory granules were increased, and exocytosis of the granules was noticed at the luminal surface. Superficial epithelial cells of the funnel-shaped pelvic wall were cuboidal in shape, and showed remarkable decrease of microridges on the luminal surface. These morphological changes of the pelvic epithelium gradually occurred until 4th week after ureteral obstruction. From these findings of the rabbit pelvic epithelium, it is suggested that transport of water and solutes of the pelvic urine can take place through the epithelia covering the renal papilla and peripelvic column, the secretory function is accomplished by the epithelium of the pelvic pouch, and the transitional epithelium related to the permeability barrier is only limited to the funnelshaped pelvic wall. In the experimental hydronephrotic kidney, it is postulated that the epithelial cell activities of the renal papilla, peripelvic column and pelvic pouch are increased and permeability barrier of the transitional epithelium is maintained until 4th week after ureteral obstruction.