Developmental changes in the distribution of corticosteroid-binding globulin in fetal and newborn sheep tissues

Developmental changes in immunohistochemical localization of corticosteroid-binding globulin (CBG) in fetal and newborn sheep tissues were studied. Tissue samples have been harvested at days 63-64, 100-103, 125-128 and 142-144 of gestation or 2 postnatal days. In the liver, immunoreactive CBG (irCBG) has been identified in hepatocytes. The intensity of CBG staining was highest at 63-64th gestation days and then was lowered gradually down to negligible level in newborn lambs. Within kidney, irCBG was selectively localized to the epithelium of proximal and distal convoluted tubules. Its amount in the course of development followed a pattern similar to that in the liver. By contrast, fetal sheep lung and pancreas demonstrated noticeable rise of irCBG late in gestation. irCBG has been detected in respiratory epithelium of tertiary bronchi, bronchioles and terminal bronchioles, meanwhile alveoli and other lung tissues were CBG-immunonegative. In the pancreas, irCBG staining was associated with acinary cells, whereas Langerhans islets contained no irCBG at all examined stages of pregnancy. Developmental changes in irCBG did not follow reported triphasic profile of fetal sheep plasma CBG concentrations thereby showing the existence of independent cellular mechanisms regulating CBG level in the tissues. Peculiarities of intraorgan distribution and developmental changes in irCBG suggest that intracellular CBG may regulate bioavailable cortisol concentrations in the sheep tissues during fetal and early postnatal life.