Renal sinus lipomatosis and body composition in hypertensive, obese rabbits

To test whether renal lipomatosis, an accretion of fat in the renal sinus associated with chronic renal infections, abscesses and calculi, can also be caused by rapid weight gain.

New Zealand white rabbits were fed either standard rabbit chow (n = 24) or chow fortified with 10% corn oil plus 5% lard (n = 25) for 8-12 weeks.

The rabbits and constituent tissues were weighed initially, after drying and after organic extractions. Renal tissue cholesterol and triglycerides were measured chemically.

Rabbits made obese by increased fat intake were 1.8 kg heavier than controls (5.5 +/- 0.3 kg vs 3.7 +/- 0.2; n = 24,25), had 1.54 kg more body fat (1.90 +/- 0.25 vs 0.36 +/- 0.11 kg/rabbit; n = 10,9), and had a mean arterial blood pressure that was 9.2 mm Hg greater than controls (95.1 +/- 8.5 vs 85.9 +/- 5.6 mm Hg; n = 23,24). Individual organs grew in mass (lung, 15%; gastrocnemius, 17%; liver, 27%; kidney, 30%) and their parenchyma gained extractable lipids (lung, 5.5 mg/g tissue; gastrocnemius, 9.6 mg/g tissue; liver, 17.9 mg/g tissue). Total renal triglycerides were increased 2.1 fold, from 103 +/- 36 to 219 +/- 59 mg/kidney (n = 8,8), compared to the 5.3 fold increase in whole body fat. Renal cholesterol was increased 1.7 fold, from 7.5 +/- 1.1 to 12.7 +/- 2.9 mg/kidney, (n = 8,8). Within experimental error, the sum of the total renal triglycerides plus the total renal cholesterol equaled the net fat extracted from the renal sinus alone: 95 +/- 29 mg/kidney in lean rabbits and 253 +/- 71 mg/kidney in obese (n = 17,17).

Obesity alone can cause renal lipomatosis. This increased volume of anatomically localized fat may be sufficient to externally compress renal veins and lymphatics, thus altering renal hemodynamic behavior.