Calciotrophic hormones during experimental hypocalcaemia and hypercalcaemia in spontaneously diabetic rats

Abstract

1, (1,25(OH) 2 D 3 ) concentrations have been found to be decreased in diabetic humans and rats. To investigate further the regulation of plasma Ca in diabetes, first we measured Ca 2+ , P, Mg, parathyroid hormone 1-34 (PTH), and total and free 1,25(OH) 2 D 3 in male spontaneously diabetic rats 7 and 28 days after the onset of glycosuria. Secondly, we studied changes in the levels of PTH and 1,25(OH) 2 D 3 in response to hypocalcaemia induced by an i.v. infusion of EGTA (2·5%, wt/vol.) for 24 h, and changes in the levels of 1,25(OH) 2 D 3 in response to an i.v. infusion of rat PTH (10 µg over 24 h) without or with concomitant EGTA infusion (producing hypercalcaemia or normo/ hypocalcaemia respectively), in diabetic and control rats. Ca 2+ , P, Mg and PTH concentrations remained within the control ranges after 7 and 28 days of glycosuria; 1,25(OH) 2 D 3 concentrations were decreased after 7, but not after 28, days of glycosuria. PTH concentrations showed a similar rise during EGTA-induced hypocalcaemia in control and diabetic rats compared with salineinfused rats, whereas 1,25(OH) 2 D 3 concentrations were unchanged in both groups. Total and free 1,25(OH) 2 D 3 levels were comparably (about 3-fold) increased during PTH, but not during combined PTH and EGTA infusion in control and diabetic rats. Total 1,25(OH) 2 D 3 concentrations were lower in the diabetic groups infused with saline or PTH than in their respective controls, and there was a similar trend in the PTH+EGTA-infused group; free 1,25(OH) 2 D 3 levels, however, were normal or increased in the diabetic groups, confirming our previous data.The novel finding of this study is that, despite severe insulin deficiency and altered 1,25(OH) 2 D 3 levels, the in vivo response of PTH levels to hypocalcaemia and the in vivo response of 1,25(OH) 2 D 3 levels to PTH in diabetic rats are comparable with those found in nondiabetic rats.

Low Levels of 25-hydroxyvitamin D3and 1,25-dihydroxyvitamin D3in Patients with Newly Diagnosed Type 1 Diabetes

“…Samples were investigated using a well−established radioimmu− noassay [16] consisting of a two−step procedure. Briefly, the as− say involved a preliminary extraction and subsequent purifica− tion of vitamin D metabolites from the serum or EDTA plasma using C 18 OH "extra clean" cartridges.…”

Vitamin D Deficiency in Guinea Pigs: Exacerbation of Bone Phenotype During Pregnancy and Disturbed Fetal Mineralization, with Recovery by 1,25(OH)2D3 Infusion or Dietary Calcium-Phosphate Supplementation

“…All assays, except Ca 2+ and 1,25(OH) 2 D 3 , were done in a single run. Ca 2+ was measured in whole blood by the ion selective electrode method on the Ciba Corning 288 Blood Gas System (Bayer Diagnostics, Brussels, Belgium); plasma P was measured by colorimetry [31]. Plasma 25(OH)D 3 was measured by direct competitive protein binding assay [32]; the detection limit of this assay is about 2.5 lg/L (6.25 nmol/L).…”

“…Plasma 25(OH)D 3 was measured by direct competitive protein binding assay [32]; the detection limit of this assay is about 2.5 lg/L (6.25 nmol/L). Plasma 1,25(OH) 2 D 3 was measured by radioimmunoassay (RIA) after HPLC puri®cation, as described [23], with later modi®cations [31]; the detection limit is around 18 pg for 1 mL plasma (43 pmol/L). Vitamin D-binding protein (DBP) was measured by a single radial immunodiusion assay speci®c for guinea pig DBP [18]; the free 1,25(OH) 2 D 3 index was calculated as the 1,25(OH) 2 D 3 /DBP molar index (´10 )5 ) [23].…”