Calcium regulation in the embryonic chick. III. Calcium and phosphate in serum and allantoic fluid of normal and shell-less embryos.

ABSTRACT

Calcium metabolism of chicken embryos was profoundly affected by incubation in shell-less culture, but phosphate metabolism was largely undisturbed. Shell-less embryos exhibited hypocalcemia and hypocalciuria relative to normal embryos but had similar levels of phosphate in serum and allantoic fluid. The concentration of calcium in allantoic fluid declined during incubation in both groups, owing largely to accompanying increases in allantoic volume, but total amounts of calcium in the allantois did not vary with time. Both normal and shell-less embryos maintained higher concentrations of calcium in serum than in allantoic fluid, with shell-less embryos maintaining a larger gradient between serum and allantoic compartments. In contrast, serum and allantoic concentrations of inorganic phosphate increased over time in both normal and shell-less embryos, and both groups maintained generally higher concentrations of inorganic phosphate in the allantoic sac than in serum. Treatment of embryos with parathyroid hormone had no effect on calcium and phosphate metabolism. Embryos maintained in shell-less culture grew more slowly than those incubated normally and consequently had a dry mass about half that of normal embryos on day 18. Shell-less embryos also exhibited abnormalities in fluid balance, which were reflected in their inability to maintain normal allantoic volume and in their higher relative hydration compared to embryos incubated in ovo.