Carbonic anhydrase in the human fetal gastrointestinal tract.

Tissues from human fetuses with a gestational age of 19-26 weeks were studied by histochemical and biochemical methods. In gastric homogenates both the catalytic activity and the immunoassayable amount of carbonic anhydrase increased with gestational age. The enzyme activity and isoenzyme pattern in a fetus of 26 weeks were similar to those found in adult gastric mucosa. High enzyme activity was demonstrated histochemically in the gastric surface epithelium at a gestational age of 19 weeks. At this age, the number of stained parietal cells was low, but it increased considerably with gestational age. In all fetal gastrointestinal tissues tested there was a total lack of capillary staining for carbonic anhydrase activity, which contrasts to the clear staining found in adult tissues. The amounts of carbonic anhydrase in the small intestine were lower in the isoenzyme HCA-B than for HCA-C. Histochemically, the staining of jejunal epithelial cells in the fetuses was clearly reduced, both on the villi and in the crypts. In the ileum, single epithelial cells on the villi were distinctly stained, a finding similar to that in adult ileal epithelial cells in the fetuses was clearly reduced, both on the villi and in the crypts. In the ileum, single epithelial cells on the villi were distinctly stained, a finding similar to that in adult ileal epithelium. The colon showed the most striking differences between fetal and adult tissues, with much lower levels of both isoenzymes HCA-B and HCA-C and less staining of the epithelium in the fetal colon. Thus, the developmental pattern of carbonic anhydrase varied considerably among the intestinal tissues. The functional significance of the differences between fetal and adult tissues is only partly understood at present.