Abstract
The appearance of carbonic anhydrase isoenzymes in rat liver and skeletal muscle during fetal and postnatal development was studied with immunohistochemistry. In the 12-day fetus the early strong expression of CA I in hepatocytes was partially replaced by the expression of CA II and CA III during late prenatal development. In the 20-day fetus the staining intensity of CA III was equal to that of a mature female rat. In the male, the staining intensity in hepatocytes clearly increased during sexual maturation. Immunoelectron microscopy showed diffuse cytoplasmic and nucleoplasmic staining of CA III in hepatocytes. The time-dependent expression of the isoenzymes in hepatocytes may reflect a different metabolic function of these structurally closely related isoenzymes. In skeletal muscle, CA III was the only isoenzyme detected during development. In late prenatal and early postnatal stages all muscle fibers contained about equal amounts of CA III. The differentiation of the muscle according to the expression of CA III occurred during the first 3 postnatal weeks.