Catecholamines and phosphate excretion by the remnant kidney

The remnant kidney (RK) exhibits an enhanced fractional excretion of phosphate (FEPi) even in the absence of parathyroid hormone (PTH). Thus, factors other than PTH contribute to this adaptive phosphaturia. Dopamine (DA) infusion is phosphaturic, whereas stimulation of adrenoreceptors is antiphosphaturic. Therefore, the hypothesis that alterations in catecholamines by the RK may be associated with the phosphaturia exhibited by this model was tested. Male Sprague-Dawley rats were subjected to right nephrectomy and surgical ablation of the left renal poles. Four weeks later rats with a RK (N = 10) and control rats with intact kidneys (N = 9) were anesthetized and thyroparathyroidectomized (TPTX). Two hours after TPTX, urine samples were collected for measurements of urinary free DA excretion. Subsequently, 3% inulin in saline was infused for one hour and a 30 minute clearance was taken. The kidneys were then removed and frozen for determination of tissue norepinephrine (NE) and DA concentrations. Glomerular filtration rate was significantly lower in rats with a RK than in controls (0.57 +/- 0.07 vs. 0.83 +/- 0.08 ml/min/g kidney wt), whereas fractional excretion of phosphate (FEPi) was significantly higher (29.4 +/- 4.7 vs. 8.3 +/- 3.4%). Tissue NE concentration was significantly lower in the RK than in the control intact kidney (85.10 +/- 4.95 vs. 129.60 +/- 7.20 ng/g), whereas urinary DA excretion per nephron was significantly higher in the RK (0.12 +/- 0.02 vs. 0.04 +/- 0.006 pg/min).(ABSTRACT TRUNCATED AT 250 WORDS)