Histochemical studies of enzymes of the energy metabolism in postimplantation rat embryos.

Using histochemical procedures for the detection of lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), and cytochrome c oxidase (cytox), we investigated the levels of these enzymes of the energy metabolism in postimplantation rat embryos (9.5-12.5 days of gestation). On day 10.5 of gestation, the neural tube, somites, myocardium, and mesenchyme displayed moderate levels of LDH activity; this activity gradually increased in strength, so that, on day 12.5 of gestation, intense LDH activity was uniformly distributed in these intraembryonic tissues. In contrast to LDH, distinct regional differences in the distribution of SDH and cytox were detected. On day 10.5 of gestation, the myocardium exhibited weak to moderate SDH and cytox activity, and on day 11.5, the myocardial activity of these enzymes had become moderate to intense. However, in all other embryonic tissues, e.g., the neural tube and somites, only weak SDH and cytox activity was present. On day 12.5 of gestation, the myocardium displayed very intense SDH and cytox activity, whereas the mantle layer of the neural tube, the spinal ganglia, and the myotomes exhibited only moderate levels of SDH and cytox activity. In the matrix of the neural tube and mesenchyme, these enzyme activities remained at low levels. At electron microscopy, cytox activity was detectable in the spaces between the inner and outer membranes as well as in the intracristal spaces of mitochondria. In general, cytox activity increased in parallel with the differentiation of mitochondria (i.e., increased mitochondrial numbers and size, and the development of mitochondrial cristae), but when the distribution of the cytox activity was considered in detail, it was found to differ among mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)