[Effect of active metabolites of vitamin D on manifestations of primary hyperparathyroidism]

We have evaluated the serum levels of 25-hydroxyvitamin D (25-OHD) and 1,25-dihydroxyvitamin D (1.25-OHD) in 33 patients with primary hyperparathyroidism and normal renal function, relating them with the clinical expression of the disease and other biochemical parameters. The level of 1.25-OHD of the patients was significantly higher than in healthy controls [51 +/- 18 vs 36 +/- 10 pg/ml (122 +/- 43 vs 86 +/- 24 pmol/l), p less than 0.001], although it was higher than the upper limit of the normal range in only 36% of patients. By contrast, the level of 25-OHD was diminished [11.0 +/- 6.3 ng/ml (27.5 +/- 15.7 nmol/l) in the patients and 19.9 +/- 10.5 ng/ml (49.7 +/- 26.2 nmol/l) in the controls, p less than 0.01]. A positive correlation was found between PTH and 1.25-OHD (r = 0.40, p less than 0.05) and a negative one between PTH and 25-OHD (r = -0.40, p less than 0.05). Calcemia was correlated with PTH (r = 0.77, less than p 0.001) but not with 1.25-OHD (partial r = 0.22). There was no correlation between vitamin D metabolites and calciuria, nor between the former and the biochemical indexes of bone remodelling. There were no significant biochemical differences between patients with renal calculi and those without them. It was concluded that PTH level appears as the major determinant factor of 1.25-OHD serum level. The serum level of vitamin D metabolites does not seem to clearly influence calcemia, calciuria, bone remodelling or the development of calculi.