Role of dopamine in the exaggerated phosphaturic response to parathyroid hormone in the remnant kidney.

The remnant kidney (RK) exhibits an exaggerated phosphaturic response to parathyroid hormone (PTH) infusion. Increased urinary dopamine synthesis per nephron has been demonstrated in the remnant kidney, and dopamine infusion is phosphaturic. Therefore, the role of dopamine in the exaggerated phosphaturic response to PTH infusion in the RK was evaluated. To obtain the RK model, Sprague-Dawley rats were anesthetized and subjected to right nephrectomy as well as surgical ablation of the left renal poles. Sham surgery was performed in the other groups of rats. Four weeks later, acute experiments were performed in these animals. Two hours after thyroparathyroidectomy, a control clearance was taken. Subsequently, PTH (33 U/kg bolus, 1 U/kg/min) was infused for 60 minutes, followed by a 30-minute experimental clearance. In the rats with an RK, the increase in the fractional excretion of phosphate (FEPi) in response to PTH infusion was (delta 38.5% +/- 4.2%, n = 12). In an additional group of rats with an RK, the specific DA-1 receptor antagonist (SCH 23390, 25 micrograms/kg/min) was infused for 30 minutes, a control clearance was taken, and then PTH was infused. Infusion of SCH 23390 significantly blunted the phosphaturic response to PTH (FEPi, delta 24.0% +/- 7.7%, n = 7). In contrast, the phosphaturic response to PTH was similar in the rats that underwent sham surgery in the presence (delta FEPi, 25.4% +/- 1.6%, n = 5) and absence of infusion of SCH 23390 (delta FEPi 24.7 +/- 3.1%, n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)