Sequential morphological changes in the pig detrusor in response to chronic partial urethral obstruction.

The sequential morphological changes which occur in the wall of the porcine urinary bladder in response to experimentally induced partial outflow obstruction have been determined using morphometric light and electron microscope techniques. The initial morphological response to urethral obstruction was a reduction of approximately 50% in the density of autonomic nerves in the bladder wall which occurred within the first 3 months. During this period the morphology of smooth muscle cells and the distribution of connective tissue were unaltered. Longer periods of obstruction produced a gradual further reduction in the density of innervation. However, from 3 months onwards the detrusor muscle bundles became infiltrated by connective tissue, although significant change in muscle cell size was not detected after obstruction for 12 months. Using electron microscopy, smooth muscle cells were observed to possess extensive amounts of perinuclear granular reticulum, this feature being particularly marked in bladders subjected to longer periods of obstruction. The underlying mechanisms responsible for these structural changes remain to be determined.