The staining showed that the urothelium of the WHHL-MI rabbits was thinner than that of controls in an age-dependent manner and that the amount occupied by muscle fibers decreased, replaced by connective tissues. The fact that bladder urothelium became thinner depending on age was a unique point in the present study. In former studies18–20 of BOO, spinal cord-injured, and bladder ischemia models, see more urothelium appeared thickened, edematous and hyperemic. One of

the reasons of bladder thickness could be compensation toward urine output resistance and acute or sub-acute experimental preparations by increasing metabolism. However, the present study reflects gradual progression of hyperlipidemia. In the chronic phase of hyperlipidemia, urothelium selleck metabolism might shift from a compensation stage to a de-compensation stage, resulting in urothelium thinning observed in old WHHL-MI rabbits. Another possible reason of urothelium thinning might be the presence and degree of inflammation or metabolic changes related to hyperlipidemia, although serum hyperlipidemia alone seems not to cause urothelium thinning.21,23 Another possibility is the effect of oxidative stress. Reactive oxygen species and reactive nitrogen species are generated by ischemia, and they could damage membrane function including L-type calcium channels, alter Ca2+ homeostasis, and increase activities of Ca2+-dependent

enzymes.19 These changes may be related to the urothelium thinning

and increased permeability of urothelium, resulting in bladder dysfunction as described below. In the frequency volume charts, the number of micturition of WHHL-MI rabbits was increased with age, and old WHHL-MI rabbits showed a significantly higher micturition number than controls, although the daily urinary volumes were not different between the groups. The micturition volume of the WHHL-MI rabbits was significantly lower than that of the control in both young and old rabbits (Table 2). In the cysotmetric study, the WHHL-MI rabbits showed non-voiding contractions, shorter interval and lower micturition volume compared to the control group. Although voiding pressures Bay 11-7085 were not significant different between young WHHL-MI and control rabbits, old WHHL-MI rabbits showed significantly lower voiding pressure than controls. The residual urine was not significantly different between the groups (Table 2). In the functional study using isolated bladder smooth muscle strips, the effects of KCl (80 mm), carbachol (10−8–10−4) and electrical field stimulation (EFS: 0.5 ms duration, 1–60 Hz and 2 sec train) were evaluated in both groups. Carbachol and EFS caused concentration- and frequency-dependent contractions in both control and WHHL-MI groups. KCl-induced contractile responses were not significantly different between WHHL-MI and control rabbits.