The inductive effect of rickets on glycolytic enzymes of rat epiphyseal cartilage and its reversal by vitamin D and phosphate

Dietary boron modifies the effects of vitamin D3 nutrition on indices of energy substrate utilization and mineral metabolism in the chick

An experiment was designed to test part of the hypothesis that physiologic amounts of dietary boron enhance utilization of or, alternatively, compensate for, inadequate concentrations of active vitamin D metabolites to normalize energy substrate utilization and mineral metabolism. Day-old cockerel chicks were fed a ground corn, high-protein casein, corn oil-based diet (< or = 0.18 mg B/kg) supplemented with physiologic amounts of boron (as orthoboric acid) at 0 (non-PSB) or 1.4 (PSB) mg/kg and vitamin D3 (as vitamin D3 powder in corn endosperm carrier) at 3.13 (inadequate, IVD) or 15.6 (adequate, AVD) micrograms/kg. After 26 days, IVD decreased food consumption and plasma calcium concentrations and increased plasma concentrations of glucose, beta-hydroxybutyrate, triglycerides, triiodothyronine, cholesterol, and alkaline phosphatase activity. In the IVD chicks, PSB returned plasma glucose and triglycerides to concentrations exhibited by the AVD chicks and increased food consumption in both IVD and AVD chicks. Histologic findings suggested that PSB enhanced maturation of the growth plate. A ninefold increase in dietary boron yielded only a two-fold increase in plasma boron concentration and no increase in femur boron concentration, which suggests that boron is under homeostatic control. The findings suggest that boron acts on at least three separate metabolic sites because it compensates for perturbations in energy substrate utilization induced by vitamin D3 deficiency, enhances major mineral content in bone, and, independently of vitamin D3, enhances some indices of growth cartilage maturation.

Initiation of endochondral calcification is related to changes in the redox state of hypertrophic chondrocytes

The level of pyridine nucleotides (NADH and NAD+) in the mineralizing growth plate of the chick was ascertained by high-resolution scanning microfluorimetry and biochemical analysis. Scanning electron microscopy and light microscopy were used to relate the concentrations of NADH and NAD+ to stages of chondrocyte maturation. A dramatic increase was found in the relative concentration of reduced pyridine nucleotides in the hypertrophic zone. On either side of this zone, in proliferating and calcifying cartilage, there was a decrease in NADH fluorescence, and the NADH/NAD+ ratio was depressed. The finding that NADH accumulated in the tissue zone associated with the earliest deposition of bone mineral supports the hypothesis that a change in the redox state initiates tissue mineralization.

Bone matrix studies. Influences of parathyroid extract, calcitonin, and cholecalciferol and of rickets and its treatment

Bones from young rats were incubated with radioactive glucosamine and proline. The concentrations and specific activities of matrix glycosaminoglycan fractions, prepared by a cetylpyridinium chloride method, and the specific activity of insoluble collagen hydroxyproline were determined. Acute parathyroid extract treatment increased labelling of hyaluronic acid and a glycopeptide fraction. These effects were partially blocked by calcitonin treatment which had no effect by itself. Parathyroid extract inhibited collagen synthesis and this effect was not blocked by calcitonin. Effects of these two hormones on labelling of chondroitin sulfate fractions were more variable. Vitamin D-3 caused an increase in labelling of all matrix fractions measured in bone from thyroparathyroidectomized rats, but its stimulating effect upon collagen synthesis was blocked by parathyroid extract. Bones from rats made rachitic on a phosphorus and vitamin D-deficient diet were incubated in vitro with radioactive glucosamine and proline. Over a three-week period rachitic bone exhibited a progressive fall in concentration and labelling of a glycopeptide-hyaluronic acid fraction, while pair-fed animals supplemented either with phosphorus alone or with phosphorus and vitamin D-3 not only remineralized their bones, but the bones showed a pronounced increment in concentration and labelling of this fraction. Both treatment regimens also enhanced chondroitin sulfate and collagen labelling.

Changes in organic matrix of bone and of bone and blood ATP in rats fed rachitogenic diets

Vitamin D deficient and phosphate deficient states were produced in young rats by the use of synthetic diets. Whole blood ATP, serum calcium and phosphorus and the ash, phospholipid, hexosamine and hydroxyproline contents of metaphyseal bones of control and rachitic rats were measured after 4 weeks on the diets. There was a decrease in whole blood ATP and serum phosphorus of the rachitic rats, and in the contents of ash, phospholipid and hexosamine of the rachitic metaphyses, while the hydroxyproline contents of the rachitic bones were higher than those of the controls. Subcutaneous injection of ATP or inorganic phosphate in rats, fed a low phosphate diet deficient in vitamin D, caused an increase in serum phosphorus and blood ATP levels and in metaphyseal ash contents. It is suggested that some of the metabolic disturbances in rickets are due to alteration in ATP production.

25-hydroxyvitamin D: autoradiographic evidence of sites of action in epiphyseal cartilage and bone

Tritiated 25-hydroxyvitamin D3 was administered to growing rats to morphologically documents its sites of action. Highly selective incorporation occurred in epiphyseal hypertrophic cells, epiphyseal matrix, osteoid, osteoblasts, and osteocytes of metaphyseal bone spicules. The labeled metabolite appeared in chondrocytic lacunar matrix coincident with hypertrophic cell death as evidenced by histological examination. The tritiated 25-hydroxyvitamin D3 became localized only in areas of active mineralization.

The comparative effects of vitamin d deficiency and ethane-1-hydroxy-1,1-diphosphonate administration on the histology and glycolysis of chick epiphyseal and articular cartilage

A comparison has been made between the effect of a vitamin D--deficient diet and treatment with disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) on the morphology of chick epiphyseal cartilage and on the production of lactate in vitro by epiphyseal and articular cartilage. The cell populations in the growth plate were different following the two treatments. Vitamin D deficiency was characterized by an increase in proliferating cells, with a relative paucity of hypertrophic cells; EHDP treatment was characterized by an increase in hypertrophic cells. When similar cell types were compared, neither treatment changed lactate production from the control value. This stresses the need to correlate the morphology of cell types with their metabolic function. The present results indicate that the major effect of vitamin D deficiency in the chick is to block the differentiation of proliferating to hypertrophic cells. In contrast, EHDP may act by inhibiting calcification directly. Even though EHDP at the doses used is known to interfere with the production of 1,25-dihydroxycholecalciferol there is no block to cell differentiation under EHDP similar to that seen in dietary deficiency of vitamin D.