Microcomputed tomography of kidneys following chronic bile duct ligation

Background. In hepatic cirrhosis, renal sodium and water retention can occur prior to decreases in renal blood flow (RBF). This may be explained in part by redistribution of the intrarenal microcirculation toward the juxtamedullary nephrons. To appreciate this three-dimensional spatial redistribution better, we examined the intrarenal microcirculatory changes using microcomputed tomography (micro-CT) in rats subjected to chronic bile duct ligation (CBDL). Methods. Six kidneys from control rats and eight kidneys from rats that had undergone CBDL for 21 days were perfusion fixed in situ at physiological pressure, perfused with silicon-based Microfil® containing lead chromate, embedded in plastic, and scanned by micro-CT. The microvasculature in the reconstructed three-dimensional renal images was studied using computerized image-analysis techniques. To determine the physiological condition of the rats, parallel experiments were conducted on six control and six CBDL rats to measure mean arterial pressure (MAP), RBF, glomerular filtration rate (GFR), urine flow (UF) rate, and sodium excretion by conventional methods. Results. The percentage of vasculature in the renal cortex from CBDL rats was significantly decreased (10.8 ± 0.4% vs. 16.8 ± 2.7% control values). However, the vascular volume fractions of the medullary tissues were not significantly altered. There were no significant differences in the number of glomeruli between groups (36,430 ± 1908 CBDLs, 36,609 ± 3167 controls). The CBDL rats had a similar GFR than the controls but a reduced MAP, RBF, UF, and sodium excretion. Conclusions. The results indicate that after CBDL, there is a selective decrease in cortical vascular filling, which may contribute to the salt and water retention that accompanies cirrhosis.