Regulation of Parathyroid Cell Gene Expression in Experimental Uremia

The secondary hyperparathyroidism of renal failure is an important component of renal osteodystrophy. We studied PTHmRNA levels and their regulation in control and subtotal nephrectomized (5/6 NX) rats at 3 wk, as well as levels of the 1,25(OH)2D3 receptor mRNA in parathyroids. Serum 1,25(OH)2D levels were decreased in 5/6 NX, whereas PTHmRNA levels were increased (7 +/- 0.7 OD U, N = 4) compared to controls (2.1 +/- 1.2, P less than 0.01); both decreased after 1,25(OH)2D3 (100 pmol/100 g body weight). Similar results were found in 5/6 NX rats after 3 months. There was no change in actin mRNA levels. PTHmRNA levels were highest in 5/6 NX rats with the most severe renal failure. The parathyroid gland 1,25(OH)2D3 receptor mRNA levels were not different between 5/6 NX rats and controls and were not affected by 1,25(OH)2D3 (100 pmol/100 g body weight daily) at 1 or 3 days. PTHmRNA levels of 5/6 NX rats did not increase when the serum calcium was decreased from 2.8 +/- 0.05 mmol/L to 0.9 +/- 0.15 mmol/L at 3 or 5 h, which contrasted with the marked increase in PTHmRNA in normal rats after hypocalcemia. As in normal rats, after hypercalcemia (4.8 mmol/L at 1 h) there was no change in the 5/6 NX rats' PTHmRNA levels. These results show that 5/6 NX rats have increased PTHmRNA levels that are normally regulated by injected 1,25(OH)2D3 but not by calcium. Parathyroid gland 1,25(OH)2D receptor mRNA levels are not increased in 5/6 NX in contrast to the increased PTHmRNA, which reflects the larger glands of uremia. 1,25(OH)2D receptor mRNA levels were not regulated by 1,25(OH)2D3.(ABSTRACT TRUNCATED AT 250 WORDS)