Moderate cholecalciferol supplementation depresses intestinal calcium absorption in growing dogs

Hormonal regulation of calcium (Ca) absorption was investigated in a cholecalciferol (vitamin D3)supplemented group (hVitD) vs. a control group (cVitD) of growing Great Danes (100 vs. 12.5 μg vitamin D3/kg diet). Although Ca intakes did not differ, fractional Ca absorption was significantly lower in the hVitD group than in the cVitD group. There were no differences in plasma concentrations of Ca, inorganic phosphate, parathyroid hormone, growth hormone or insulin-like growth factor I between groups. Plasma 25-hydroxycholecalciferol [25(OH)D3] concentrations were maintained in the hVitD dogs at the same levels as in the cVitD dogs due to increased turnover of 25(OH)D3 into 24,25-dihydroxycholecalciferol [24,25(OH)2D3] and 1,25-dihydroxycholecalciferol [1,25(OH)2D3]. In hVitD dogs, the greater plasma 24,25(OH)2D3 concentration and the enhanced metabolic clearance rate (MCR) of 1,25(OH)2D3 indicated upregulated 24-hydroxylase activity. The increased MCR of 1,25(OH)2D3 decreased plasma 1,25(OH)2D3 concentrations. In hVitD dogs, the greater production rate of 1,25(OH)2D3 was consistent with the 12.9-fold greater renal 1 α-hydroxylase gene expression compared with cVitD dogs and compensated to a certain extent for the accelerated MCR of 1,25(OH)2D3. The moderately decreased plasma 1,25(OH)2D3 concentration can only partially explain the decreased Ca absorption in the hVitD dogs. Intestinal vitamin D receptor concentrations did not differ between groups and did not account for the decreased Ca absorption. We suggest that 24,25(OH)2D3 may downregulate Ca absorption. Chemicals/CAS: 25-Hydroxyvitamin D3 1-alpha-Hydroxylase, EC 1.14.-; Calcitriol, 32222-06-3; Calcium Radioisotopes; Calcium, 7440-70-2; Calcium, Dietary; Cholecalciferol, 67-97-0; Cytochrome P-450 Enzyme System, 9035-51-2; Phosphates; Receptors, Calcitriol; Steroid Hydroxylases, EC 1.14.-; vitamin D 24-hydroxylase, EC 1.14.

Comparison of deposition images obtained by use of an ultrafine 99m-technetium-labeled carbon dry aerosol with ventilation images obtained by use of 81m-krypton gas for evaluation of pulmonary dysfunction in calves.

OBJECTIVE: To characterize the accuracy of an ultrafine 99m-technetium-labeled carbon dry aerosol for use in assessment of regional ventilation in calves with pulmonary dysfunction. ANIMALS: 7 Belgian White and Blue calves. PROCEDURE: The ultrafine aerosol was assessed by comparing deposition (D) images with ventilation (V) images obtained by use of 81 m-krypton (81mKr) gas via D-to-V ratio (D:V) image analysis in calves during spontaneous breathing (SB) and during experimentally induced pulmonary dysfunction (ePD). RESULTS: Mismatching index (LrTot) calculated on the D:V images revealed a good match (LrTot, 0.96 +/- 0.01) between D and V distribution patterns in calves during SB. Calculation of the ultrafine aerosol penetration index relative to 81mKr (PIRel) revealed preferential distribution of the ultrafine aerosol in lung parenchyma (PIRel, 1.13 +/- 0.11). In ePD, heterogeneity in the D:V distribution was observed (LrTot, 0.78 +/- 0.10) as a result of ultrafine aerosol particles impaction in airways as indicated by PIRel (0.66 +/- 0.16) and a proportion of pixels more radioactive in D images, compared with V images, that was located in the central part of the lung (475 +/- 77% in ePD vs 32.8 +/- 5.7% in SB). However, this central deposition did not prevent visual examination of the entire ventilated lung. CONCLUSIONS AND CLINICAL RELEVANCE: The ultrafine aerosol appears suitable for use in examination of ventilated parts of lungs of cattle, even those with impaired pulmonary function. However, airway impaction of ultrafine aerosol particles impedes the quantification of regional ventilation in cattle with abnormal lung function