Important things remain to be learned of the regenerative capacity of various mammal species - such as the way in which rats can regrow large sections of the bladder. Researchers investigate mechanisms of natural regeneration with an eye to finding ways to reproduce exceptional examples of regrowth in human biochemistry. Here, scientists suggest that regeneration of the bladder in rodents is a better avenue of investigation than the well known regeneration of the liver that even we humans are capable of:
Subtotal cystectomy (STC; surgical removal of ~75% of the rat urinary bladder) elicits a robust proliferative response resulting in complete structural and functional bladder regeneration within 8-weeks. ... Although regeneration per se occurs throughout the animal kingdom, there are large disparities in the degree of regeneration observed between species (e.g., amphibian versus mammalian) let alone amid organs (e.g., liver versus kidney). The extensive attention focused on regenerative medicine is understandable given the enormous potential for repair and/or replacement of old, damaged or diseased cells, tissues and organs; such as the diseased and dysfunctional bladders that are the subject of this report.
The liver is very efficient in repairing or regenerating its mass, which occurs as a direct result of the proliferation of all the existing cells from the remaining liver remnant, but is mainly driven by mature hepatocytes, which will re-enter the cell cycle to restore the liver. The entire process, which is usually referred to as regeneration, is completed within a couple weeks, depending upon the mammalian species. However, the process is more accurately termed compensatory hyperplasia.
These well established observations regarding liver re-growth stand in contrast to rodent bladder regeneration, which occurs over a longer time frame (8 weeks rather than 2 weeks), and moreover, results in a regenerated bladder that structurally and functionally is essentially identical to the native bladder which it replaced. More specifically, the bladder capacity and bladder wall thickness (as well as the presence of all three layers; urothelium, muscularis propria and lamina propria) of the regenerated bladder are indistinguishable from the previous native bladder, and moreover, the animals are entirely continent. To our knowledge, bladder regeneration therefore holds a unique position with respect to its regenerative potential, as there is no other mammalian organ capable of this type of regeneration.