Effect of Partial Bladder Outlet Obstruction on the Morphology of Elastin in Rabbit Bladder Smooth Muscle

Objectives: Elastin, in association with collagen, allows the body's organs to stretch and relax. Collagen and elastin, the major components of connective tissue, are present throughout the bladder wall and are intimately related to bladder compliance. The present study was undertaken to evaluate elastin morphologically using immunostaining and electron microscopy in the rabbit model of partial bladder outlet obstruction (PBOO). Methods: Four groups of Japanese white rabbits underwent either PBOO by mild ligation of the urethra (2- and 4-week PBOO) or no obstruction (2- and 4-week sham). Histopathological examination was performed by Elastica van Gieson staining, scanning electron microscopy, transmission electron microscopy, and ultra-high voltage electron microscopy. The number of pixels representing elastin fibers in computerized images was analyzed using Adobe Photoshop Version 2.0. Results: Bladder weight significantly increased after PBOO. Increase in the thickness of the bladder wall was observed after obstruction on histopathological examination. On scanning electron microscopy, elastin was very thick and was found in large configurations. 3-D analysis using electron microscopic tomography revealed that elastic fibers in the bladder had a coil-like appearance in the muscle layer, with each fiber composed of several fibrils. Such structures may be closely related to the physiological function of the bladder. Conclusion: Elastin in the bladder assumes the form of a coil during micturition. We examined that the increase in elastin makes it difficult for elastin to stretch linearly resulting in reduced elasticity. This change may be one of the factors involved in the decrease in compliance mediated by PBOO.