Effect of the calcimimetic NPS R-467 on furosemide-induced nephrocalcinosis in the young rat

Background. Furosemide induces nephrocalcinosis in both humans and animals. We showed previously that parathyroidectomy protected against the development of furosemide-induced nephrocalcinosis in young rats, indicating a possible role for parathyroid hormone (PTH) in its pathogenesis. Calcimimetic agents such as NPS R-467 are potent and selective agonists at the calcium-sensing receptor in parathyroid glands and inhibit PTH secretion. Methods. To determine whether NPS R-467 could, like parathyroidectomy, prevent furosemide-induced nephrocalcinosis, we studied 35 6-week-old male Sprague-Dawley rats, divided into five groups. Group A served as control, group B received intraperitoneally furosemide (40 mg/kg), groups C, D, and E received furosemide and NPS R-467 intraperitoneally at doses of 10, 20, and 40 μmol/kg, respectively, daily for 8 days. During the last 3 days, animals were placed in metabolic cages for measurement of urine output, food, and water intake. Blood and kidneys were collected on day 8, 60 to 90 minutes after the last doses. Kidney calcium content was measured and nephrocalcinosis scoring (0 to 5) was assessed histologically. Results. Furosemide increased urine output and fluid intake, and decreased body weight gain similarly in all groups. Serum PTH levels (mean ± SD) were significantly higher in furosemide-treated control animals (276 ± 226 pg/mL vs. 64 ± 21 pg/mL); NPS R-467 induced a dose-dependent decrease in PTH levels (52 ± 51 pg/mL, 18 ± 7 pg/mL, and 13 ± 3 pg/mL in groups C, D, and E, respectively). Plasma Ca²⁺ was slightly, but significantly lower in all three NPS R-467 treated groups (5.1 ± 0.4 mg/dL, 4.8 ± 0.3 mg/dL, and 4.5 ± 0.3 mg/dL in groups C, D, and E, respectively) compared to 5.7 ± 0.1 mg/dL and 5.5 ± 0.2 mg/dL in groups A and B, respectively. Furosemide treatment induced a substantial increase in kidney calcium content (1819 ± 664 μg/g dry weight vs. 126 ± 26 μg/g dry weight) and nephrocalcinosis scoring (5.0 ± 0.0 vs. 0.0 ± 0.0). Treatment with NPS R-467 ameliorated the furosemide-induced increase in kidney calcium content (673 ± 312 μg/g, 361 ± 188 μg/g, and 563 ± 291 μg/g) and nephrocalcinosis scoring (2.2 ± 1.2, 0.7 ± 0.8, and 1.0 ± 1.2) in groups C, D, and E, respectively. Conclusion. The calcimimetic agent NPS R-467 prevents the development of hyperparathyroidism and attenuates nephrocalcinosis in the furosemide-treated young rat.