Effects of diet and aging on renal measurements in uninephrectomized geriatric bitches

Under controlled, but varied dietary conditions among geriatric, uninephrectomized Beagle bitches (dogs) observed for 4 years, renal size increase as assessed radio graphically and ultrasonographically occurred at variable rates, but on a seemingly continuous basis. The maximum observed mean renal linear parameter increase found was ≈ 15%. However, a 10 and 15% increase is a more representative expectation among the 4 parameters (sonographic length, radiographic length, sonographic width, radiographic width) under consideration. The rate of renal size increase was rapid during the first 2 to 3 months following uninephrectomy. Thereafter, the rate of increase was slow, but occurred to varying degrees in both the length and width as assessed radiographically or ultrasonographically. The mechanism creating the size change was hypertrophy, not hyperplasia. Within limits of the 3 diets used in the study, no significant diet effect was found on the rate or degree of long term compensatory hypertrophy. Radiographically and ultrasonographically measured renal length had the greatest correlation with each other as well as with post mortem measurements and are, therefore, the recommended parameter for imaging assessment of compensatory hypertrophy. When the prenephrectomy, radiographic renal lengths and widths were normalized as a ratio of the second lumbar vertebral body length (L₂) measured from ventrodorsal radiographs, the diet group means across dogs (approximately three L₂ lengths for renal length; two L₂ lengths for renal width) were in the middle of the respective previously published normal radiographic ranges for mature dogs (e.g. 2.5 L₂ ≤ length ≤ 3.5 L₂; 1.58 L₂ ≤ width ≤ 2.38 L₂ lengths). Even after the hypertrophic changes occurred, the radiographic group mean lengths and widths across dogs were still within the specified normal ranges, although toward the upper end of the respective range. This information provides background for clinical interpretation of potential compensatory hypertrophy that may be encountered following uninephrectomy for spontaneous disease in aged dogs. In addition, it appears that available radiographic renal linear ranges for normal mature dogs are applicable to geriatric dogs as well.