Limitations and Impacts of the Renal Portal System on the Determination of the Glomerular Filtration Rate Using Contrast-Enhanced Computed Tomography and Plasma Clearance of Iohexol in Bearded Dragons (Pogona vitticeps)
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
Due to unique anatomy, physiology, and interspecific variation, renal disease can be challenging to diagnose and treat in reptiles.4 The glomerular filtration rate (GFR) is an indicator of renal function and has been commonly used in human and veterinary medicine. The plasma clearance of iohexol (PCI) and contrast-enhanced computed tomography (CT) have been used to determine the GFR in healthy and diseased individuals.1-7 This pilot study was initially designed to determine the GFR of bearded dragons (Pogona vitticeps) using contrast-enhanced CT and PCI. Ten bearded dragons were used for this study. Dynamic images of the kidneys were obtained sequentially every 2.5 sec for 2 min after an intravenous injection of iohexola (600 mg/kg) via a catheter placed in the ventral coccygeal vein. Time-attenuation curves were constructed and GFR was obtained using Patlak plot analysis. Individual kidney and global GFR were calculated. Plasma iohexol concentration was measured at three time points (4 h, 8 h, and 12 h after iohexol administration) using high-performance liquid chromatography, and GFR was calculated. The average global GFR was 1.52±0.98 ml/min/kg using contrast-enhanced CT and 0.24±0.06 ml/min/kg using PCI. The correlation between the two methods was poor. The renal portal system, and at times the lymphatic system, could be visualized on CT images and evidently impacted GFR calculations using both techniques. This study highlights the limitations for GFR measurements in bearded dragons and raises questions on the reliability of the ventral coccygeal vein for research purposes such as pharmacokinetic studies.
aOmnipaque, 300 mg/ml, Amersham Health, Princeton, NJ, USA
The authors thank Linda Archer, Robin Bast, Hollie Chiles, and Rachel Henriquez for their assistance with data collection.
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