Enzyme histochemistry in the developing suprarenal gland of human embryos.

The localization of the activities of some selected phosphatases, peptidases and dehydrogenases were studied in cryostat sections of the developing anlage of the suprarenal gland of human embryos from 8 to 20 weeks of the intra-uterine life. In the youngest fetuses under our notice (weeks 8-12), the activity of alkaline phosphatase (AP) on the cellular membranes of the fetal cortex was very low. In contrast, the activity of acid phosphatase (AcP) was comparatively high. Peak activity was found in the cells of the central zone of the fetal cortex. Compared to the activity of the latter, the activity of non-specific esterase (ANE) was somewhat lower. Both its localization and the gradient were identical with those of acid phosphatase. Of the peptidases studied, only dipeptidyl peptidase IV (DPP IV) exhibited slight activity in deeper layers of the primitive fetal cortex after week 8. The other peptidases exhibited only traces of activity. As early as in the first stages followed, the activity of glycero-3-phosphate-dehydrogenase (alpha-GPDH) was very high in all cells of the differentiating fetal cortex. The intensity of the activity of succinate dehydrogenase (SDH) was markedly lower. In older fetuses (weeks 13-20) there was a gradual increase in the activities of most enzymes, seen, after week 15 of the intrauterine life, also in the cells of the so-called definitive cortex. Most pronounced were the increases in the activities of acid phosphatase and non-specific esterase. The relatively low activities of the enzymes under study point to a relatively low degree of cell differentiation of both the primitive and, after week 15, the definitive cortex. Pronounced morphological and functional changes occur after the 20th week of the intrauterine life.