A kinetic study of the effects of δ-aminolevulinic acid upon the synthesis of embryonic and fetal hemoglobins in the blood islands of the developing chick blastodisc

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Abstract
Chick blastodiscs contained and synthesized a functional (embryonic) hemoglobin as early as the stage of the definitive primitive streak. The rate of hemoglobin synthesis in ovo rose dramatically at about the stage of the 3-somite embryo.Embryos explanted onto solid media at the 3-somite stage of development continued to synthesize hemoglobin in vitro for at least 12 h. The rate of synthesis rose markedly at the 6-somite stage of development, coincident with the onset of rapid synthesis of fetal hemoglobin. A supplement of exogenous aminolevulinic acid markedly stimulated the synthesis of hemoglobin before the 6-somite stage of development, but had little or no effect thereafter. These responses were obtained on both minimal and rich media. Levels of hemoglobin formed were characteristic of the final stages of development attained, regardless of initial stage of development, medium used, or time of incubation required to attain the final level of development.A new regulatory process resulting in elimination of a requirement for continuous presence of egg homogenate for maximal rates of hemoglobin was revealed. This took place between the 6- and 8-somite stages of development at the time of onset of rapid synthesis of fetal hemoglobin.
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