Effect of age on the response to short-term partial bladder outlet obstruction in the rabbit

OBJECTIVE: To compare the physiological and structural changes after short-term partial bladder outlet obstruction (PBOO) in young and old rabbits, as PBOO results in marked contractile and histological alterations in the bladder. MATERIALS AND METHODS: In all, 20 young (7-8-week-old) and 20 old (2 years old) male rabbits were divided into four subgroups of five each (four obstructed and one sham control rabbit). The rabbits in the groups were evaluated after 1, 3, 7 and 14 days of PBOO, respectively. At the end of the respective periods, cystometry and contractile responses to field stimulation (FS), ATP, carbachol and potassium chloride were determined. Full-thickness sections of the bladder body and base were used to determine the vascular density, nerve density and smooth muscle/collagen ratios. RESULTS: The bladder weight of young rabbits increased at 1-7 days of PBOO and returned toward control levels at 14 days of PBOO, while in old rabbits it was higher than the control during the entire experiment. For the young rabbits, the responses to field stimulation decreased progressively for 1, 3 and 7 days, and increased significantly at 14 days. For old rabbits there was a progressive decrease to a minimal response by 3 days of PBOO and the response remained at this level over 14 days. The contractile response to ATP, carbachol and KCl were similar to the responses to FS. The vascular density in both groups increased to a maximum at 7 days and then decreased toward control values at 14 days. For the young rabbits, nerve density decreased more than in old rabbits. In the old group, the smooth muscle/collagen ratio was increased throughout PBOO and was higher than in young rabbits. The connective tissue compartment was markedly greater than in the young rabbits and the basal mucosa had vacuoles which were not apparent in the young bladders. CONCLUSIONS: This study shows that the adaptive changes to PBOO are faster in young rabbit bladders than in older rabbits.