Assessment of Aging Effects on Computed Tomographic Glomerular Filtration Rate in Dogs

The purpose of this study is to assess the relationship between glomerular filtration rate (GFR) and age by using dynamic computed tomography (CT) and Patlak plot analysis in dogs. Fifteen dogs were used in this study. CT-GFR study was performed under general anesthesia using propofol and isoflurane. 1 ㎖/㎏ dosage of 300 ㎎I/㎖ iohexol was administered at a rate of 3 ㎖/s during GFR measurement. CT-GFR was determined with a single-slice dynamic acquisition and Patlak plot analysis. The individual and global GFR values were calculated to plasma clearance per body weight (㎖/min/㎏). Bodyweight (mean ± SD) ranged from 2.0 to 5.7 ㎏ (3.31 ± 1.13 ㎏). Age ranged from 3 years to 13 years old (7.14 ± 3.30). Mean ± SD creatinine (0.53 ± 0.34 ㎎/㎗), phosphorus (4.1 ± 1.2 ㎎/dL), and albumin (3.3 ± 0.3 ㎎/dL) concentrations and urine protein-to-creatinine ratios (all ratios were ＜ 0.5) were within reference ranges. Abdominal ultrasonography revealed small-sized renal calculi, mineralization, or renal cyst at eight dogs. The global CT-GFR ranges shown in this study was 2.57 to 6.60 ㎖/min/㎏. In this study, there was no trend toward weight-adjusted CT-GFR with increasing age. We found no relationships between age-related kidney dysfunction in fifteen dogs. Small-sized renal calculi or cysts did not affect renal function in this study. However, it is thought that a large sample size may have been required to document an age effect.