The ontogenesis of calcium-binding protein in fetal rat kidney.

The presence of calcium-binding protein (CaBP) in the nucleus and cytoplasm of epithelial cells of renal tubules varies with the physiologic state. As part of a study to determine whether or not intranuclear CaBP precedes intracytoplasmic CaBP in the same cell, we used peroxidase-labeled antibody against human renal CaBP to localize CaBP in fetal rat kidney tubules. This paper reports examination of kidneys from rats on each day of gestation from the 10th to term (21 days) and on each of the first seven postnatal days. CaBP was first detected in fetal rat kidneys on the 19th gestational day. The histochemical staining reaction that revealed the CaBP was less intense than that produced in kidneys from adult animals, but its distribution was like that in adults, with some cells having no CaBP, others having it in the cytoplasm only, in the nucleus only, or in both. By the seventh postnatal day the staining reaction was similar to the adult patterns in all respects.