The establishment of essential and metabolically derived @entity535 profiles in developing XXXX embryo organs.

@entity2226 @entity1522 @entity1246 @entity1160 @entity368 @entity535 @entity2230 @entity1853 @entity1573 @entity6778 @entity367 @entity4857 @entity815 @entity669 @entity2574
The accumulation of certain essential and metabolically derived @entity1522 in the free @entity535 pools of three excitable tissues has been studied in the @entity1573 embryo. Valine together with @entity368 are at the onset present in the yolk at higher concentrations than any of the other essential @entity1522 . By 15 days all the @entity1522 studied have accumulated in the embryonic pools at a higher rate than valine, although certain @entity1522 , such as @entity815 or @entity1853 , always remain at lower relative concentrations than @entity4857 . This reflects their low supply in the yolk, rather than a more rapid rate of disappearance (utilization). During early embryogenesis (E2-E4), tissues preferentially concentrate @entity367 , besides @entity2226 and @entity2230 (6). The next distinct stage of development (E4-E7) is marked in the brain by a gradual rise in @entity367 , @entity1160 and @entity2574 ; the same three @entity1522 do not demonstrate a further increase in the pool of the heart, while in the whole eye the @entity535 profile begins to resemble the blood. @entity368 in all three tissues declines rapidly, to reach @entity6778 levels by day 7 of development; @entity669 increases slowly in apparent reciprocity to an equally gradual @entity815 decrease. Into the second week of embryo growth (E7-E15), @entity1246 appears in the mesencephalon (E7) and the eye (E9-E10). In the mesencephalon, the free @entity535 pool composition exhibits a rather sudden increase of most metabolically derived @entity1522 .(ABSTRACT TRUNCATED AT 250 WORDS)
