Increased catabolism of 25-hydroxyvitamin D in patients with partial gastrectomy and elevated 1,25-dihydroxyvitamin D levels. Implications for metabolic bone disease

Serum vitamin D metabolites and PTH were measured in seven subjects with a history of previous partial gastrectomy (PGX) and metabolic bone disease. The elimination t 1/2 of [H-3]25-hydroxyvitamin D-3 ([H-3]25OHD(3)) in serum was assessed after an iv pulse dose of 5 mu Ci [26,27-H-3]25OHD(3). Median serum 25OHD(3) was 37.5 (27.5-101.3) nmol/L, [normal range (NR) 10.8-58.5 nmol/L], mean serum 1,25-dihydroxyvitamin D [1,25-(OH)(2)D-3] was raised at 175 +/- 72 pmol/L, (NR 48-120 pmol/L) and mean PTH was also high, 67 +/- 27 ng/L, (NR 10-60 ng/L). Serum t 1/2 [H-3]250HD(3) ranged from 10.9-21.2; days. A strong negative correlation existed between t 1/2 [H-3]250HD(3) and serum 1,25-(OH)(2)D-3 [Spearman's rank correlation coefficient (r = -0.82, P = 0.002)] and PTH [Spearman's rank correlation coefficient (r = -0.81, P = 0.001)]. Four subjects who had high initial PTH concentrations (60-115 ng/L) and elevated 1,25-(OH)(2)D levels (162-300 pmol/L) were reassessed after calcium supplementation to suppress secondary hyperparathyroidism (2 degrees HPT). In this subgroup, after-treatment PTH fell from 82 +/- 24 to 52 +/- 24 ng/L (mean +/- SD), not significant; 1,25-(OH)(2)D fell from 210 +/- 61 to 116 +/- 28 pmol/L, P = 0.015; and t 1/2 [H-3]25OHD(3) increased from 13.2 +/- 1.9 to 18.9 +/- 3.1 days, P = 0.012. Patients with PGX and evidence of 2 degrees HPT with elevated 1,25-(OH)(2)D have a reduced t 1/2 [H-3]25OHD(3), and this may explain the increased susceptibility of the subjects to osteomalacia. Calcium supplementation suppresses 2 degrees HPT, increases t 1/2 [H-3]25OHD(3) and may protect against PGX osteoporosis and osteomalacia.