Renal size and composition in hypertensive, obese rabbits

Abstract

OBJECTIVE: To determine whether the renal growth associated with obesity is due to hypertrophy or hyperplasia.

DESIGN: New Zealand white female rabbits were fed either standard rabbit chow (n=17) or chow foritified with 10% corn oil plus 5% lard (n=18) for 12–16 weeks.

MEASUREMENTS: All rabbits were weighed, and intra-arterial blood pressures were successfully measured at the end of the study in 16 lean and 18 obese rabbits; percent water of entire kidneys (8 lean, 8 obese rabbits) and of defined regions of kidneys (8 lean, 10 obese rabbits) were obtained gravimetrically. Renal hemoglobin, protein and DNA was measured chemically (8 lean, 8 obese rabbits).

RESULTS: Kidneys grew in size as the rabbits gained fat. In a series of 8 lean and 8 age-matched obese rabbits, weighing 3.7±0.1 kg and 5.4±0.4 kg (P<0.05), the kidneys were 20% larger in the obese rabbits: 15.0±0.9 g vs 18.0±2.5 g (P<0.05). Kidney protein was also 20% greater in the obese rabbit: 1.38±0.06 g/kidney vs 1.66±0.06 g/kidney (P<0.05). While total renal DNA was 16% greater in the obese: 18.2±0.5 μg/kidney vs 21.1±0.6 μg/kidney (P<0.05), no significant difference existed when the DNA was expressed as μg/mg protein. Fractional water content of the intact kidney declined with obesity: 78.7±1.1% vs 76.0±1.2% (P<0.05). Conversely, the hemoglobin content of the kidney at autopsy, an estimate of the unstressed vascular volume, increased with obesity: 55±19 mg/kidney vs 82±25 mg/kidney (P<0.05). By contrast, water content of renal parenchyma was constant: 80.8±1.0% vs 80.9±1.2% (cortex); 84.0±0.8% vs 83.6%±2.0% (outer medulla); and 85.7±0.8% vs 86.0±2.1% (inner medulla).

CONCLUSION: The renal growth associated with obesity was predominantly hyperplastic and was associated with a partial exclusion of fluid from the renal sinus.