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At least 235 records · Page 13Linked to original sources
PubMed1988

Ultrastructural study of hypervitaminosis D induced arterial calcification in Wistar rats.

Hypervitaminosis D produces extensive vascular alterations which are similar to Monckeberg's calcinosis. The present study was undertaken to examine early changes in vascular ultrastructure of rats receiving tap water supplemented with either calcium chloride or a relatively low dosage of irradiated ergocalciferol ad libitum for 21 days. Untreated rats received normal tap water ad libitum. A significant increase in serum calcium levels was obtained in hypervitaminosis D treated rats. Calcium deposits were seen near the internal elastic lamina, within new elastic elements and around degenerating smooth muscle cell fragments in the extracellular organic matrix of hypervitaminosis D treated rats. Calcium deposits were not detected in vascular sections from untreated rats or those receiving calcium chloride. A complex pathogenesis of vascular lesions produced by hypervitaminosis is suggested. One possible pathogenic mechanism for calcification of elastic matrix may be via altered microfibrils. Our data support this hypothesis and indicate that much lower levels of vitamin D administration, compared to other reports, produce considerable vascular calcinosis in this experimental preparation. Several hypotheses regarding possible mechanisms of pathologic calcification are discussed.

Animals↗
PubMed1987

Nitrendipine-stimulated release of prostacyclin-like substance in normal and atherosclerotic animals.

Nitrendipine (Bayotensin) is a dihydropyridine derivative that appears to preferentially dilate peripheral vessels by a cellular mechanism similar to those found with other calcium blocking agents. In this study nitrendipine when infused (0.2-0.3 mg/kg i.v.) into anaesthetized cats caused a release of a substance disaggregating platelet clumps which had adhered to blood superfused collagen strip. The appearance of this unstable disaggregating substance was prevented by the pretreatment of cats with acetylsalicylic acid (50 mg/kg i.v.). In atherosclerotic rabbits nitrendipine stimulated release of prostacyclin-like substance without effect on proaggregatory concentrations of arachidonic acid and adenosine diphosphate. In rats nitrendipine inhibited the development of atherosclerotic changes in the aorta evoked by the atherogenic diet with ergocalciferol (vitamin D2). It is suggested that nitrendipine may promote formation of prostacyclin in arteries and inhibit the development of atherosclerosis.

Animals↗
PubMed1985

Improved radioimmunoassay for vitamin D and its use in assessing vitamin D status.

We describe a faster, more-sensitive radioimmunoassay for vitamin D in plasma. Antibodies were generated in rabbits immunized with a new vitamin D analog, the 23,24,25,26,27-pentanor-C(22)-carboxylic acid of vitamin D, coupled directly with bovine serum albumin. After several months, Rivanol-treated sera from the rabbits contained high-titer antibodies, as determined by their abilities to bind 25-hydroxy-[3H]cholecalciferol. The antibody, used at a 1:15 000 final dilution, cross reacted equally with all cholecalciferol and ergocalciferol metabolites tested except 1,25-dihydroxycalciferol metabolites and the parent calciferols. 25-Hydroxycalciferol and similar forms were efficiently extracted from plasma or serum with acetonitrile. We separated bound from free 25-hydroxy-[3H]cholecalciferol by using a second antibody: goat antiserum to rabbit serum. The detection limit of the assay was 3.0 pg of 25-hydroxycholecalciferol and its equivalents per tube; thus only 1 microL of plasma is needed per assay tube. Results compared well with those from a liquid-chromatographic procedure involving specific ultraviolet detection of 25-hydroxycalciferol in plasma.

Animals↗
PubMed1994

[Glucocorticoid-induced osteopenia].

This article reviews the pathogenesis of glucocorticoid-induced osteopenia (GIO). GIO is a result of direct and indirect mechanisms leading to: 1) decreased intestinal calcium absorption, 2) decreased renal calcium reabsorption, 3) increased osteoclast activity with increased bone resorption, 4) decreased osteoclast activity with decreased bone formation. The mainly osteoclast activity is raised on the basis of secondary hyperparathyroidism. The different possible treatments in order to prevent GIO are reviewed on the basis of the results of the most important studies about the subject. We conclude that before a secure recommendation about prophylactic treatment can be made more prospective studies with fracture incidence as a measure should be made. However, on the basis of the studies that have already been made, it seems rational to give patients in longterm glucocorticoid treatment a calcium supplement of 0.5-1 g/day either in tablet form or by changing the diet, combined with a vitamin-D supply: either ergocalciferol 600-800 IU/day (e.g. in the form of 2 multivitamin tabs/day) or calcitriol 0.5 microgram/day.

Bone Diseases, Metabolic↗
PubMed1994

[Convulsions and neonatal hypoparathyroidism revealing maternal hyperparathyroidism].

BACKGROUND: Severe prolonged hypocalcemia may occur in neonates whose parathyroid hormone production has been blocked by maternal hyperparathyroidism. This report describes such a case. CASE REPORT: A 7 day-old girl was admitted suffering from dyspnea and repeated convulsions that had continued for 2 days. Her birthweight was 3,500 g and her height 50 cm. Her mother had been given an iron preparation and calcium during pregnancy. Clinical examination of the newborn at birth revealed a cleft palate and micrognathia. The baby had been given milk-formula plus ergocalciferol, 1,200 IU/day. At admission, the baby was hypotonic. Her serum total calcium was 1.27 mmol/l; total proteins 61 g/l; ionized calcium 1.1 mmol/l; phosphorus 2.14 mmol/l; intact PTH 21 pg/ml (N = 10-65) and 25(OH)D 8 ng/ml (N = 8-30). She was given intravenous calcium gluconate (1 g/m2/d), diazepam (0.5 mg/kg) rectally, intravenous phenobarbital (20 mg/kg) but intravenous phenytoin was needed to stop clinical and electrical seizures. Her blood calcium was normalized 5 days later. Her mother, who was clinically normal, had: total serum calcium: 2.72 and 2.77 mmol/l; total proteins: 71 g/l; phosphorus: 0.85 mmol/l; intact PTH: 73 pg/ml; 25(OH)D: 6 ng/ml; Ultrasonography showed an adenoma of the right parathyroid. Further studies on the baby showed no signs of Di George syndrome. CONCLUSION: Neonatal hypocalcemia always requires investigation of both the infant and mother. Measurements of vitamin D metabolites and intact PTH are required to recognize maternal hyperparathyroidism.

Female↗
PubMed1993

Determination of vitamin D status by radioimmunoassay with an 125I-labeled tracer.

We report here the first radioimmunoassay for a vitamin D metabolite utilizing a radioiodinated tracer. Antibodies were generated in a goat immunized with the vitamin D analog 23, 24, 25, 26, 27-pentanor-C(22)-carboxylic acid of vitamin D, coupled directly with bovine serum albumin. The 125I-labeled tracer was prepared by reacting a 3-amino-propyl derivative of vitamin D-C(22)-amide with Bolton-Hunter reagent. The primary antiserum, used at a 15,000-fold final dilution, cross-reacted equally with all cholecalciferol and ergocalciferol metabolites tested except 1,25-dihydroxycalciferol metabolites and the parent calciferols; the antiserum did not cross-react with dihydrotachysterol. Calibrators were prepared in vitamin D-stripped human serum. 25-Hydroxycholecalciferol was quantitatively extracted from serum or plasma (50 microL) with acetonitrile. The assay consists of a 90-min incubation at room temperature with primary antiserum, followed by a 20-min incubation with a second antiserum and separation of bound from free fractions by centrifugation. The detection limit of the assay was 2.8 micrograms/L for 25-hydroxycholecalciferol. Results with the present assay compared well with those from a liquid-chromatographic procedure involving specific ultraviolet detection of 25-hydroxycalciferol in plasma.

25-Hydroxyvitamin D 2↗
PubMed1995

Phytosterols as growth regulators.

Starting from squalen and gonan structures, nature produces by enzymatic transformation a great variety of P--and subsequently also of "animal" sterols. This wonderful chain of biosyntheses comprises a number of provitamins such as beta-carotene and ergosterol and has an endpoint in the vitamin D compounds ergocalciferol (ercalciol, vit D2) and cholecalciferol (calciol, vit D3). On the other hand, we have has an endpoint the most important compound cholesterol and its derivatives, like androsterone, testosterone and 17 beta-estradiol. The members of this family of chemical compounds perform the most diverse biological functions, if properly "directed" or transported to their respective sites of action. Since all of these compounds are hardly soluble in water, we concentrated our research work on their solubilization and thus on enhancing their bioavailability and bioreactivity. The bioreactivity of P was taken as guiding principle for an investigation into understanding the ways of nature as closely as possible-and, at same time-to interpret the findings in comprehensive context. An effort at integrated system's thinking was made throughout.

Biological Availability↗