phosphorus-radioisotopes and Vitamin-D-Deficiency

Topics: Animals; Biological Transport; Calcium; Chickens; Cholecalciferol; Intestinal Absorption; Intestinal Mucosa; Intestine, Small; Phosphates; Phosphorus Radioisotopes; Protein Binding; Vitamin D Deficiency

A new, completely in vivo method of measuring the rate of intestinal phosphate absorption has been developed. As expected from previous in vitro and ex vivo measurements, intestinal phosphate absorption is potently and rapidly stimulated by 1,25-dihydroxyvitamin D3. The response is saturated with as little as 11.3 ng of 1,25-dihydroxyvitamin D3 per day, consistent with a genomic mechanism. The effect of 1,25-dihydroxyvitamin D3 disappears when the dosing solution of phosphate is at 2 M, suggesting that 1,25-dihydroxyvitamin D3 stimulates active transport of phosphate but not diffusion of phosphate. Finally, unlike findings resulting from in vitro or ex vivo experiments, no evidence in vivo was obtained that phosphate absorption requires sodium or is inhibited by potassium.

Topics: Absorption; Animals; Calcitriol; Dose-Response Relationship, Drug; Intestinal Mucosa; Male; Osmolar Concentration; Phosphates; Phosphorus; Phosphorus Radioisotopes; Potassium Compounds; Rats; Rats, Sprague-Dawley; Time Factors; Vitamin D Deficiency

The rates of diffusion of small ions and neutral molecules through isolated calvaria have been determined. Compared with data published on self-diffusion and diffusion through cartilage, H2O, 3-O-methylglucose, lactate, sulfate, and methylamine diffuse at approximately 2/3 the expected rate. Diffusion of H2O and sulfate was unaffected by the administration of the diphosphonate 1-hydroxyethane-1,1-diphosphonate (EHDP), although phosphate fluxes are markedly diminished. Diffusion of water was nearly doubled by vitamin D deficiency. A 1-week treatment with 1,25(OH)2D3 had no effect on H2O diffusion while returning calcium influx to normal. It is concluded that bone matrix permits a flow of small neutral and ionized molecules nearly comparable to that in cartilage. When changes in calcium and phosphate influx are observed, they can be ascribed to the exchange properties of bone mineral and not to changes in matrix permeability.

Topics: 3-O-Methylglucose; Animals; Body Water; Bone and Bones; Calcium; Carbon Radioisotopes; Diffusion; Kinetics; Lactates; Lactic Acid; Male; Methylglucosides; Phosphorus Radioisotopes; Rats; Rats, Inbred Strains; Sulfates; Sulfur Radioisotopes; Tritium; Vitamin D Deficiency

The concentration of inorganic sulfate-sulfur in the serum of vitamin D-deficient rats, 2.6 to 3.5 mg. per cent, was found to be higher than that in the serum of normal rats of the same age, 2.0 mg. per cent. No change was observed following the administration of 25 gamma of vitamin D(2). In accord with the results of others, it was found that a definitely increased deposition of phosphorus in femurs and tibiae had occurred 36 to 48 hours after the administration of vitamin D(2) to vitamin D-deficient rats. An immediate increase in the uptake of sulfate by the skeleton was found using sodium sulfate-S(35). As measured by the specific activity of sulfate-sulfur in samples of chondroitin sulfate isolated from the skeletons of the vitamin D-deficient animals and from normal controls receiving equal doses of sulfur-35, the rate of synthesis of chondroitin sulfate in rachitic rats is similar to the rate in normal rats of the same age. Likewise, the incorporation of labelled sulfate into the sulfomuco-polysaccharides of the pelts was found to be equal at 12 hours to that in normal rats. Following the administration of vitamin D(2) to deficient animals an increase in the rate of synthesis of the chondroitin sulfate of the skeletons was noted. The radiochemical and radioautographic evidence suggest that there is in vitamin D-deficient rats an impaired utilization of chondroitin sulfate and that vitamin D(2) is able to accelerate this process.

Topics: Animals; Cartilage; Chondroitin Sulfates; Ossification, Heterotopic; Osteogenesis; Phosphorus; Phosphorus Radioisotopes; Rats; Sulfates; Sulfur; Sulfur Radioisotopes; Vitamin A; Vitamin D; Vitamin D Deficiency; Vitamins