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Development of the amino acid pools in chick embryo brain, heart, and eye: Taurine, valine, glutamine, and phosphoethanolamine
Author(s) -
van Gelder N. M.,
Bélanger F.
Publication year - 1988
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.490190115
Subject(s) - glutamine , valine , amino acid , medicine , biology , embryogenesis , endocrinology , embryo , taurine , yolk sac , choroid plexus , embryonic heart , biochemistry , embryonic stem cell , microbiology and biotechnology , central nervous system , gene
The redistribution of valine, from the nonrenewable yolk supply into excitable tissues, was studied during the first 15 days of chick embryogenesis. Valine levels in the extraembryonic circulation (the vitelline plexus) peak between days 7–9 (E 7–9 ) and then decline steeply. In their first phase of differentiation (E 2 –E 4 ), all embryonic tissues contain more valine than the blood plexus. From E 4 to E 7 , the heart and brain exhibit initially a rapid fall in valine, but from day 7 on the decrease becomes more gradual. The eye during the same period reaches an equilibrium with circulating valine; as these levels fall from E 9 to E 15 , the eye retains the valine that accumulated. Against this pattern of change, characteristic for an essential amino acid during embryogenesis, glutamine levels are at any time from two‐ to threefold higher than valine in all tissues. In the circulation, this ratio remains constant throughout the 15 days of embryonic development. Eye glutamine, higher on day 4, by E 7 has entered into an equilibrium with glutamine in the plexus. A steady but two times higher glutamine level is maintained in the heart, although during the later stages of development it gradually tends to approach the plexus content. In sharp contrast, starting on E 7 and accelerating on E 9 , a large increase of glutamine relative to valine or other essential amino acids is seen in developing brain tissue. This appears typical for most metabolic amino acids, suggesting that by days 9–10 the essential acid supply in the brain is being exhausted. Phosphoethanolamine, present in very low concentrations in the nutritional supply, is actively extracted by the plexus and other embryonic tissues. By day 4, tissue levels are five times higher than in the circulation. From then on, apparently sequestered pools of phosphoethanolamine in the heart and eye gradually diminish as the embryo matures. The brain continues to accumulate the metabolite until day 9. Taurine sequestration in the eye is saturated by day 4, and then appears to enter into an exchange equilibrium with the circulation. The heart steadily accumulates taurine during the entire embryonic period when levels are three to four times higher than in the plexus. Brain tissue is most active in taking up taurine, but the process has reached its limits by day 7. This limit is determined by the amount of taurine available in the yolk, since injections of taurine in the nutritional supply result on day 7 in a further increase in the brain. The heart, too, is able to sequester extra taurine but not before day 9 of embryogenesis. The eye, however, does not seem to develop a further capacity to sequester more taurine than is usually supplied by the circulation.