A large animal model of bladder exstrophy: Observations of bladder smooth muscle and collagen content

Purpose: The development of adequate bladder capacity is not ensured in all patients with bladder exstrophy despite successful bladder closure and rec onstruction. To determine the factors leading to the development and matura tion of the exstrophic bladder we created a large animal model of exstrophy . We compared biopsies obtained from a cohort of experimentally induced exs trophic neonatal sheep bladders to those of normal control bladders and rel ated the findings to a previously reported comparison of human neonatal nor mal and exstrophic bladders. Materials and Methods: Bladder specimens of 7 newborn lambs with experiment ally induced exstrophy were compared to specimens of 10 newborn control lam b bladders. All specimens were stained with Masson's trichrome as well as w ith specific monoclonal antibodies to types I and III collagen. Stained sec tions were then analyzed using a morphometric image analysis system to quan tify the amounts of smooth muscle and collagen present. Results: A significant increase in the ratio of collagen-to-smooth muscle w as noted in exstrophic versus normal control bladders (p <0.05). This diffe rence was similar to that in the previous study of neonatal human bladders. There was no significant difference in the ratios of types I and III colla gen in the 2 groups of sheep bladders. This finding is different from that reported in the previous human studies. Conclusions: Overall changes in the ratio of smooth muscle-to-collagen in t he sheep exstrophy model are similar to those in humans. However, the diffe rences in collagen types I and III do not seem to be present.