Study design, materials and methods
Forty eight rats were randomly divided into eight groups, with 8 animals in each group. Rats of first seven groups were executed cystometry on 1, 3,5,7,11,15 and 21days after cystostomy in conscious condition, while rats of group 8 with no cystostomy as control group. Parameters of basal bladder pressure(Pves,basal), maximum bladder pressure(Pves,max,），bladder threshold pressure(Pves,thre), voiding interval（VI）, duration of urination(DU) which refered to the time that bladder pressure curve suddenly rose followed Pves,thre to recover to Pves,basal, bladder compliance( △C), voiding volume(VV), post voiding volumn(PVR) and bladder capacity(BC) been compared among first 7 groups and parameters of BC, VV, PVR were compared between the first 7 groups and control group. After cystomery we collected rats’ bladders for bladder weighting and hematoxylin–eosin (HE) staining.
Cystometric parameters of all groups show as table 1.The trends of Pves,basal, Pves.max, Pves,thre were downward, while BC, IV, VV and △C were upward from 1 to 5 days after cystostomy in conscious rats(figure 1). The BC and VV were reduced significantly on 1 and 3 days after cystostomy than control group(0.33±0.19, 0.43±0.19 VS 1.23±0.42 (p<0.01), 0.32±0.19, 0.42±0.19 vs 1.23±0.42 (p<0.01)). During 5 to 15 days after cystostomy the parameters of Pves,basal, Pves.max. Pves,thre,VI, VV, BC and PVR had no significant different among first 7 groups, while BC, VV and PVR had no significant different between the first 7 groups and control group. The BC increased significantly on 21 days after cystostomy. Bladder weight in experiment groups all were greater than control group, among experiment groups the bladder weight increased 1 and 3 days after cystometry, then reduced and kept stable during 5-15days after cystostomy, then increased significantly again on 21 days after cystostomy. HE staining showed diffuse neutrophils and lymphocytes infiltrated in both the lamina propria and muscularis propria, apparent edema was found in lamina propria and muscularis propria and surface ulcerations were in urothelium layer on 1 and 3 days after cysostomy. During 5-15 days after cystostomy bladder inflammation was mild which there was just little lymphocytes infiltrated in lamina propria. On 21 days after cystostomy, more fibrin deposited in the lamina propria was found in rats’ bladders.
Interpretation of results
The present experiment showed BC and VV were smaller significantly on 1 and 3 days after cystostomy than control group indicating that bladder function was not stable at 1 and 3 days after cystostomy.This was in accord with T. L. YAKSH who also found there would be overactive bladder(OAB) condition in rat’s bladder in the first few days after cystostomy. The bladder weight and HE stain showed rat’s bladder was in acute inflammation on 1 and 3 days after cystostomy. The bladder weight in rats of 1 and 3 days after cystostomy were bigger than 5-15 days, while there were scattered bleeding spots on the bladder wall. H-E stain showed there was numerous neutrophils and lymphocytes infiltration in the lamina propria and smooth muscle layer, edema in bladder tissue and mucosal ulcer in urothelium layer, which was the reason for OAB condition. So when cystometry in conscious rats during 1-3 days after cystostomy should be avoided or the results should be carefully explained.
During 5 to 15 days after cystostomy the Pves.max. Pves,thre, VI, VV, BC and PVR had no significant different among the first 7 groups, while BC, VV and PVR had no significant different between the first 7 groups and control group, it indicated that rats’ bladders became stable at 5-15 days after cystostomy and the changes of histology were in agreement with the changes of cystometric parameters. The bladder weight had no significant different during 5-15 days compared with each other after cystostomy, and HE-stain showed the inflammation was mild that there had little lymphocytes infiltration in the lamina propria indicating the pathological changes were minimal at this stage. This phase should be the best time window for study bladder function.
Study show the BC on 21 days after cystostomy were greater than control group and the trend of BC was upward from 1 to 21 days after cystostomy which indicated that BC increased gradually until 21 days after cystostomy. At the same time bladder weight was increased significantly at 21 days after cystostomy, and there were more fibrin located in lamina propria. The reason of BC changed at this stage was unclear.