with these renal deposits indicates that they have merely become inactive and that the associated tissue injury has resolved. We devel- oped and tested our hypothesis in a rat model of renal crystal deposi- tion. METHODS: Male Sprague-Dawley rats (n=30) were given hydroxy-L-proline (HLP) mixed with chow. Rats in group 1 (Fed, n=15) continued on hydroxy-L-proline for 63 days while rats in group 2 (Early, n=15) stopped taking HLP after 42 days. Urine was collected and analyzed once weekly for creatinine, calcium, oxalate, lactate dehydro- genase (LDH), 8-isoprostane (8-IP) and H2O2. Urinary pH and crys- talluria were monitored. Rats from each group (n=5) were sacrificed on days 28, 42 and 63. Renal tissue was examined for crystal deposition and markers of inflammation osteopontin (OPN) and ED-1 (macro- phage stain). RESULTS: All rats receiving HLP developed CaOx nephrolithi- asis by day 42. Urinary excretion of LDH, 8-IP and H2O2, markers of stress and injury, increased significantly in all rats compared to base- line. Additionally, immunohistochemical staining for OPN (renal epithe- lial cells) and ED-1 (renal interstitium) was stronger in all rats compared to baseline (p0.001). In the early HLP discontinuation group, signifi- cant decreases in urinary oxalate, 8-IP, H2O2, and urinary crystals were noted compared to urine of the fed group (p0.01). Histologically, a statistically significant reduction (p0.001) in crystal deposition, OPN, and ED-1 staining was noted in Early vs. Fed groups. CONCLUSIONS: Administration of HLP lead to renal CaOx crystal deposition with the development of inflammation and associated degradation in renal biology. Discontinuation of HLP caused a de- crease in urinary excretion of oxalate and a reduction in CaOx crystal renal deposition. As a result, renal structure and function returned to normal with resolution of injury and inflammation. These results indi- cate that, over time, crystal deposition can be reversed, inflammation can be resolved, and renal structural changes can be restored. This suggests that the absence of inflammation and injury at any specific time does not indicate its prior non-existence. Source of Funding: RO1 DK065658-03S1 (BKC) and R01 DK065658-04 (SRK) 1973 THE EFFECT OF CHITOSAN ON UROTHELIAL PERMEABILITY, URETERAL INTRALUMINAL DRUG ADMINISTRATION AND PERISTALSIS Donald Pick*, Stanislav Shelkovnikov, Noah Canvasser, Narges Alipanah, Phillip Mucksavage, Jason Lee, Michael Louie, Elspeth McDougall, Ralph Clayman, Orange, CA INTRODUCTION AND OBJECTIVES: Chitosan is the deacety- lation product of chitin and has been demonstrated to disrupt urothelial barrier of the bladder. In an ex vivo model, intraluminal nifedipine has been shown to relax the ureter. Relaxing the ureter prior to endourology procedures could ease instrument access. Continuing our work with medications to increase ureteral permeability, we study the effect of 1 M nifedipine on peristalsis before and after pretreating the ureter with chitosan. METHODS: Using freshly harvested porcine ureters, 4 cm intact tubular segments were placed in a novel organ bath with gassed Krebs solution. Both ends of the ureter were cannulated. A pressure transducer was placed in-series at the inflow end of each ureter. Outflow drained by gravity. Intraluminal flow (1 ml/min) was maintained by a gravity fed constant pressure reservoir. To induce peristalsis, phenylephrine (10 M), was added to the external bath. Nifedipine (1 M) was then added to the intraluminal reservoir. The time required to stop peristalsis was measured. Chitosan (0.5% w/v, 30 minutes) was then used to treat the urothelium and the study repeated. RESULTS: Intraluminal nifedipine (1 M) had no effect on ureteral peristalsis after 60 minutes of exposure in six trials. After pretreatment with chitosan, nifedipine (1 M) stopped ureteral peristal- sis within an average of 12.30  1.93 minutes. Ureteral contractile amplitudes were similar (p=0.53) before and after chitosan adminis- tration. Histological analysis of the ureter before and after pretreatment with chitosan showed no urothelial disruption. CONCLUSIONS: By pretreating the intraluminal surface of the ureter with chitosan nifedipine reversibly blocks peristalsis at low con- centrations. Chitosan changes ureteral urothelial permeability, but has no long-term effect on ureteral contraction. Source of Funding: None 1974 ROLE OF TOTAL ANGIOTENSIN BLOCKADE ON RECOVERABILITY OF RENAL FUNCTION AFTER RELIEF OF CHRONIC PARTIAL UNILATERAL URETERAL OBSTRUCTION. Shady Soliman*, Ahmed Shokeir, Ahmed Mosbah, Hassan Abol-Enein, Nashwa Barakat, Essam Abou-Bieh, Ehab Wafa, Mansoura, Egypt INTRODUCTION AND OBJECTIVES: To evaluate of the effect of total angiotensin blockade (ACEI (enalapril) + angiotensin receptor blocker losartan ) on prevention of deterioration of renal function during partial unilateral ureteral obstruction (PUO) and to study their impact on enhancement of recoverability of renal function after relief of obstruc- tion. METHODS: Fifty six male mongrel dogs were classified into 5 groups: sham (8; sham surgery + no medications), control (12; left PUO + no medications), and 3 study groups; 12 dogs each; left PUO + either enalapril; losartan or combination. The study and control groups were subjected to 4 weeks PUO. After that, dogs of the control and study groups were reopened and subjected to Lich-Grigoir uret- erovesical re-implantation. Dogs of the control and the study groups were sacrificed by the 8th week after relief of obstruction after being evaluated at basal condition, by the end of the 4th week of obstruction and at 4 and 8 weeks after relief of obstruction by measurement of selective endogenous creatinine clearance, selective renographic clearance and renal resistive index (RI). Dogs of the sham group underwent sham surgery at basal, 4 and 8 weeks and were subjected to same evaluation. RESULTS: Sham surgery showed no significant impact on any of the evaluated parameters. Compared with the control, combination therapy saved reduction of creatinine clearance by 13% of the basal value and saved reduction of the renographic clearance by 20 % of the basal value by the end of the 4th week of obstruction. During PUO, combination therapy adds no significant benefit compared with the use of either drug alone. The renoprotective effect after 4- week obstruction was 18 % for the losartan, 12% for the enalapril and 20 %for the combination. Moreover, compared with the control, combination ther- apy enhanced regain of creatinine clearance by 18 % of the basal value and enhanced regain of renographic clearance by 34 %. Combined therapy significantly enhanced recoverability of renal function com- pared with either drug alone. Compared with the controls, enhance- ment of the recoverability of renal function after 8 -week relief of 4- week obstruction was 24 % for the losartan, 23% for the enalapril and 34 %for the combination (P0.001). In addition, the increase of RI was significantly less in the three study groups. CONCLUSIONS: Total angiotensin blockade decreases dete- rioration of renal function in partial UUO and enhances recoverability of renal function after relief of obstruction. The effect was more pro- nounced during recoverability phase. Source of Funding: None e766 THE JOURNAL OF UROLOGY Vol. 183, No. 4, Supplement, Wednesday, June 2, 2010