Samuel Edelstein

1,25-Dihydroxyvitamin D3 and the regulation of macrophage function

SummaryVitamin D3 deficient (D−) mice show a depressed inflammatory response and both inflammatory peritoneal macrophages and bone marrow polymorphonuclear leukocytes of D− mice exhibit a decreased spontaneous migration under agarose. The impaired phagocytic response of peritoneal macrophages from D− mice can be corrected by incubation with 1,25-dihydroxyvitamin D3 and is not affected by interaction with other vitamin D3 metabolites. Transfer of mice from the D− to the D+ state results in correction of both the inflammatory and the phagocytic response. Intactness of phagocyte function is thus directly dependent on vitamin D3 metabolism.

Vitamin D and Its Hydroxylated Metabolites in the Rat

Replacing body stores of vitamin D in pregnant rats with radiolabelled cholecalciferol, enabled the measurement of cholecalciferol and its hydroxylated metabolites in fetal tissue. Elevated levels of 24, 25-dihydroxycholecalciferol were found to be present in fetuses, with highest accumulation in the skeleton. A similar finding was observed when tritiated 24,25-dihydroxycholecalciferol was administered continuously to pregnant rats. When tritiated 1,25-dihydroxycholecalciferol was administered, very little was transported into the fetuses, and out of the transported fraction a major portion was found to be esterified. A selectivity pattern was established for the lacteal transport of cholecalciferol and its hydroxylated metabolites, in the order: cholecalciferol > 25-hydroxycholecalciferol > 24,25-dihydroxycholecalciferol > 1,25-dihydroxycholecalciferol. Vitamin D sulfoconjugates were not detected in suckling rat pups, and over 80% of the lacteal-transported 1,25-dihydroxycholecalciferol in suckling pups was found to be esterified. It is suggested that rat fetuses and newborn pups do not require 1,25-dihydroxycholecalciferol, that a protective mechanism against vitamin D intoxication operates in fetuses and pups in the form of esterifying enzymes, and that 24,25-dihydroxycholecalciferol might be associated with bone metabolism.

Maternal-perinatal interrelationships of vitamins D metabolism in rats

In pregnant rats it has been possible to show that the distribution of cholecalciferol metabolites in their fetuses reflects the distribution of these metabolites in the blood. In these experiments, pregnant rats were maintained on a vitamin D deficient diet but were supplemented with radiolabelled cholecalciferol. The metabolites found were 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol and, to a lesser extent, cholecalciferol. 1,25-Dihydroxycholecalciferol was not detected in fetal tissues, despite the ability of fetal kidney homogenates to hydroxylate 25-hydroxycholecalciferol in C-1. Kidney homogenates of newborn pups were found to possess marked activity of 25-hydroxycholecalciferol-24-hydroxylase, which was retained even in hypocalcemic pups born to pregnant rats that were fed a low-calcium diet. Injection of radiolabeled cholecalciferol to newborn pups resulted in the formation of 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol. 1,25-Dihydroxycholecalciferol was not detected. Tissues thought of as target organs for vitamin D (in pregnant rats), namely, intestine, kidney and bone, were found to contain none or very little 1,25-dihydroxycholecalciferol. Mammary glands obtained from lactating rats were found to contain mainly the unchanged vitamin.

The functional metabolism of vitamin D in chicks fed low-calcium and low-phosphorus diets.

Radioactively labelled cholecalciferol was administered continuously to chicks that were fed normal, low-calcium and low-phosphorus diets. It has been possible to show that under such steady state conditions with regard to cholecalciferol, and mineral restriction, the animal reacts by increased accumulation of 1, 25-dihydroxycholecalciferol in the intestinal and the kidney cell, which was associated in the intestine with an increased calcium-binding activity. A similar accumulation of 1, 25-dihydroxycholecalciferol in bone was not noticed. It is proposed that the intestine and the kidney, but not bone, are the main target organs for cholecalciferol in the maintenance of calcium homeostasis, and that both calcium and phosphorus play a role in the regulation of the formation and subsequent function of 1, 25-dihydroxycholecalciferol.

Involvement of cholecalciferol metabolism in birds in the adaptation of calcium absorption to the needs during reproduction

1. The metabolism of calcium and cholecalciferol in quail (Coturnix coturnix japonica) and chicken (Gallus domesticus) during maturation was correlated to gonadal activity and plasma oestrogen levels. 2. Birds with undeveloped ovaries (immature), developed ovaries but not laying (mature), and after laying 3-8 eggs (laying), were used in the first series. 3. Birds in which egg production had been arrested by Nicarbazin, were used in the second series. 4. Plasma 17 beta-oestradiol and calcium were elevated in the mature bird, with no further change in the laying bird. Kidney 25-hydroxycholecalciferol-1-hydroxylase and intestinal calcium-binding protein increased slightly in the mature bird, whereas they were grossly elevated in the laying bird. 5. Calcium and phosphorus absorption were markedly elevated in the laying bird. 6. No changes were noted in plasma 25-hydroxycholecalciferol, at any stage of maturation. 7. During the arrest of egg production by Nicarbazin, 17 beta-oestradiol level, calcium concentration of plasma, and medullary bone were maintained. Kidney 25-hydroxy-cholecalciferol-1-hydroxylase, intestinal calcium-binding protein and absorption of calcium were strikingly reduced. 8. The results suggest that changes in calcium absorption and cholecalciferol metabolism during maturation in birds are not directly affected by gonadal hormones; they appear to represent an adaptation to the increased calcium needs due to medullary bone formation and, more importantly, to the large losses of calcium imposed by shell formation.

Decrease in bone levels of 1,25-dihydroxyvitamin D in women with subcapital fracture of the femur

SummaryIn a previous study we were able to show that in women over the age of 45 the level of 1,25-dihydroxyvitamin D (1,25(OH)2D) in bone, but not in serum, is significantly reduced when compared with younger women. In the present study we measured the concentration of 1,25(OH)2D in sera and bones of 19 female patients with subcapital fractures of the femur, mean age 78±2 years. We were able to show that serum levels of 1,25(OH)2D were within the normal range, while bone levels were markedly reduced compared to levels in femoral bone obtained from young female cadavers or to the previously reported levels in non-osteoporotic elderly women. Thus, reduced levels of 1,25(OH)2D in bones of elderly women may lead, together with other factors, to subcapital fractures.

Use of the β‐carotene rich alga Dunaliella Bardawil as a source of retinol

Abstract 1. Dunaliella bardawil, a β‐carotene accumulating halo‐tolerant alga, has been tested as a source of retinol in a chick diet. 2. Chicks were fed diets deficient in retinol or supplemented with retinol, synthetic β‐carotene or dry algae. 3. After an initial lag, chicks grew equally well on diets supplemented with algae, retinol or β‐carotene. 4. Serum and liver analyses revealed a normal content of retinol in all chicks except those grown on the retinol‐deficient diet. Chicks fed the algae‐supplemented diet contained lutein but no β‐carotene in their serum, even though the ratio of β‐carotene to lutein in the algae was over 15:1. 5. Laying hens fed with an algae‐supplemented diet showed enhanced egg yolk colour attributable to a higher lutein content. No β‐carotene was present in the egg‐yolk. 6. These studies demonstrate the possibility of using dried Dunaliella bardawil as a dietary supplement which can fully satisfy the retinol requirement and also serve as a yolk‐colour enhancing agent.

Levels of active metabolites of vitamin D3 in the callus of fracture repair in chicks.

The levels of the active metabolites of vitamin D were measured in the callus and in the epiphyseal growth plate of chicks given radioactive cholecalciferol during fracture healing. Those levels were correlated with the histological findings. Three groups of chicks were studied: a control group with no fracture, chicks with fractures fixed by Kirschner wire, and chicks with unfixed fractures. A significant increase in the levels of the active metabolites was found in the callus during the first few days after fracture. The levels of 25-hydroxycholecalciferol [25(OH)D3] and of 24,25-dihydroxycholecalciferol [24,25(OH)2D3] were higher when there was no fixation, while those of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] were higher after fixation. The concentrations of these metabolites in the proximal epiphysis of the tibia were similar to those found in the callus. Based on these findings it is suggested that the active metabolites of vitamin D are directly involved in the process of fracture repair.

Response of renal calcium-binding protein. Independence of kidney vitamin D hydroxylation.

Dietary calcium and dietary phosphorus restriction were studied in chicks fed either cholecalciferol or 1alpha-hydroxycholecalciferol. Intestinal calcium absorption and calcium-binding protein of 1alpha-hydroxycholecalciferol-treated chicks remained unchanged under dietary calcium restriction, but increased under dietary phosphorus restriction. Kidney calcium-binding protein was not altered by dietary caclium restriction in chidks treated with either cholecalciferol or 1alpha-hydroxycholecalciferol, but increased under dietary phosphorus restriction independent of the vitamin D source. In contrast to the intestine, calcium-binding activity of the kidney was found to be poorly related to the calcium-binding protein concentration. It is suggested that kidney calcium-binding protein is regulated by a mechanism different from that of intestinal calcium-binding protein, and that its concentration in renal tissue is related to renal caclium excretion or plasma calcium level.

Contrasting effects on bone formation and on fracture healing of cholecalciferol and of 1 α-hydroxycholecalciferol

SummaryExperimental fractures were performed on tibiae of vitamin D-depleted chicks. The chicks were divided into three groups; they were treated daily with (a) cholecalciferol or (b) 1α-hydroxycholecalciferol (1α(OH)D3), or (c) they received no treatment. Microscopic examination of the calluses formed at the fractured sites and of the proximal tibiae of the contralateral legs showed that treatment with 1α(OH)D3 failed to heal most of the rachitic signs seen in the nontreated chicks, despite normal plasma concentrations of calcium and of inorganic phosphorus.In a second experiment, experimental fractures were performed on tibiae of chicks that were fed a vitamin D-deficient diet, but were dosed continuously with radioactive cholecalciferol. Analysis of cholecalciferol metabolites in the callus tissue showed perferential accumulation of 25-hydroxycholecalciferol (25(OH)D3) and of 24,25-dihydroxycholecalciferol (24,25(OH)2D3). Very little 1α, 25-dihydroxycholecalciferol (1α,25(OH)2D3) was detected in bones or in calluses.Based on the data obtained, the following conclusions were drawn: (a) that cholecalciferol is directly involved in bone formation; and (b) that 1α, 25(OH)2D3 is not the sole metabolite of cholecalciferol involved in this process.