An ultrastructural study of the effect of thyroxine on embryonic chick liver development
Smith, Stephen Lee
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The effect of thyroxine, injected on day 6 of incubation, on embryonic chick liver development was examined morphologically and histologically. An ultrastructural comparison of thyroxine-treated to nqn-treated was done on prepared liver specimens in addition to body weight and liver weight gains. Liver weight increased in thyroxine-treated embryos substantially on day 11 of incubation and continued through day 14 of incubation. No increase in body weight was observed in comparison to non-treated embryos. As early as day 10 of incubation, embryonic chick hepatocyte mitochondria were shown to be capable of binding thyroxine and responded by swelling, suggesting that thyroxine receptor development precedes thyroxine synthesis and secretion. Total mitochondrial membrane surface area, as a result of mitochondrial swelling, in relation to hepatocyte cytoplasmic area was found to be more important than individual parameters, such as total number of mitochondria per hepatocyte and individual mitochondrial area. Mitochondrial swelling and subsequent increase in membrane surface area may be significant in terras of oxidative phosphorylation and ATP synthesis.