Passive Properties of the Urinary Bladder of Neonatal Rat Compared with Adult Rat

Ha, Tea Joon; Oh, Seung June; Choi, Hwang

Abstract

PURPOSE: Bladder compliance increases during gestation, in which the role of collagen is considered important. However, it has been reported that the compliance paradoxically decreases without clear explanation after birth. Previous in vitro strip study showed that neonatal urinary bladder was stiffer than that of adult in rats. Herein, we extended our previous study.
MATERIALS AND METHODS
Urinary bladders were removed from male Sprague-Dawley rats, 1 to 3-day old neonate and 12 week-old adult. Volume-pressure relationship was obtained using in vitro whole bladder study: in the consideration of anatomical difference in bladder wall thickness and zero pressure volume, all parameters were corrected as stress and stretch. Relative collagen content of the bladder was assessed and compared using image analysis after Masson?s Trichrome stainging in two groups.
RESULTS
Volume-pressure analysis revealed that the patterns of increase of stress according to stretch were different between two groups; exponential coefficient of the slope of neonatal bladders was larger, which means neonatal bladder proved to be stiffer than that of adult. Collagen ratio to muscle in the bladder muscle layer was not different between adult and neonatal rats(p.>0.05), while adult rat bladder has more collagen deposition in mucosal layer(p<0.05).
CONCLUSIONS
Our results from previous length-tension relationship and volume-pressure relationship demonstrated that neonatal bladder was stiffer than adult bladder, which was inexplainable with collagen contents. Other factors than collagen might be suggested in determination of passive properties in the development of urinary bladder.