Effects produced by the administration of high doses of 1,25-dihydroxycholecalciferol to the chick embryo

Abstract

White Leghorn chick embryos were injected on the 15th day of incubation with 70 to 300 pmoles 1,25-(OH)2D3. All doses produced hypercalcemia; with the highest dose, the concentration of calcium in serum started to rise 4 h after the injection, reached a peak 20 h after, and was still high 48 h after. Twenty hours after the injection of the same dose, the concentration of inorganic phosphorus in the serum was significantly lower than in the corresponding controls. The tibias from 17-day-old chick embryos injected with 300 pmoles on day 15 were shorter, lighter, and had a lower ash content than those from controls. Histological signs of resorption appeared to be reduced with respect to controls, but no precise quantitation was conducted. The fact that hypercalcemia was not accompanied by hyperphosphatemia may suggest that the vitamin stimulates resorption of calcium from the shell, which is mainly formed by calcium carbonate rather than from the bone from which calcium and phosphate are usually resorbed together.

The Distal Nephron in the Chick Embryo as a Target Tissue for 1-Alpha-25-DihydroxycholecaIciferoI

“…Narbaitz and Tolnai [1978] showed that the injection of 1,25-DHCC into chick embryos produces hypercalcemia and sug gested that this results from an increase in the resorption of calcium through the chorioallantoic membrane. In support of this suggestion, Narbaitz et al [1980] dem onstrated the presence of receptor cells for 1.25-DHCC in the choriollantois and Nar baitz et al [1981a] showed that the hormone is capable of increasing carbonic anhydrase activity in the membrane; this enzyme is responsible, at least in part, for the solubili zation of the shell mineral.…”

Hypervitaminosis D in the chick embryo: Comparative study on the activity of various vitamin D3 metabolites

“…Similar changes have been observed in young chicks [17]. Narbaitz and Tolnai [8] have shown that the injection of 1,25(OH)2D 3 to chick embryos on the 15th day of incubation produces hypercalcemia but that this is accompanied by hypophosphatemia rather than hyperphosphatemia. Our present results confirm this observation and show that similar response can be obtained as early as the 9th day of incubation.…”

“…A first series of experiments was carried out to find out if the peripheral rim of unmineralized (osteoid) trabeculae which had been described previously [8] in the bones from embryos injected with 1,25(OH)zD 3 on the 15th day of incubation could also be induced at earlier ages. These experiments showed that the characteristic bone changes could be induced only when 1,25(OH)2D 3 was injected on the 1 lth day of incubation or later.…”

“…Since hypercalcemia was accompanied by hypophosphatemia, it was suggested that the hormone acted by increasing calcium absorption from the shell (which contains calcium but not phosphate) rather than from the yolk or bones from which calcium and phosphate are generally resorbed simultaneously [8]. This suggestion was later supported by the demonstration that 1,25(OH)2D 3 produces an increase in carbonic anhydrase activity in the chorioallantoic membrane which follows the same time course as the increase in the concentration of calcium in the blood [9].…”

“…The administration of large doses of 1,25(OH)zD 3 to 15-day-old chick embryos has been shown to produce hypercalcemia and bone alterations characterized by the subperiosteal proliferation of unmineralized trabeculae in the diaphysis of long bones [8]. Since hypercalcemia was accompanied by hypophosphatemia, it was suggested that the hormone acted by increasing calcium absorption from the shell (which contains calcium but not phosphate) rather than from the yolk or bones from which calcium and phosphate are generally resorbed simultaneously [8].…”