Expression of the Subtype 2 Angiotensin (AT2) Receptor Protein in Rat Kidney

In situ hybridization studies have suggested that the subtype 2 angiotensin (AT2) receptor gene is expressed in fetal and newborn rat kidney but is undetectable in the adult animals. In the present study, we investigated the expression of AT2 receptor protein in the fetal (days 14 and 19 of fetal life), newborn (day 1 postpartum), and adult (4-week-old and 3-month-old) rat kidney. Polyclonal anti-peptide antiserum was raised against the amino terminus of the native AT2 receptor. The selectivity of the antiserum was validated by recognition of the AT2 receptor in a stably transfected COS-7 cell line by Western blot and immunocytochemical analysis. As a positive control, the AT2 receptor signal was detected strongly in the adrenal gland. Positive immunohistochemical staining was observed in the mesenchymal cells and ureteric buds of the 14-day fetal kidney and in the glomeruli, tubules, and vessels in the 19-day fetal and newborn kidney. Glomeruli expressing the AT2 receptor were localized mainly in the outer layer of the renal cortex. In the young (4-week-old) and mature (3-month-old) adult rat on normal sodium intake, renal AT2 receptor immunoreactivity was present in glomeruli but substantially diminished compared with that of newborn rats. In both young and mature adult rats, dietary sodium depletion increased the renal AT2 receptor signal, mainly in the glomeruli and interstitial cells. Preimmune and preadsorption controls were negative. Western blot analysis detected a single 44-kD band in the fetal and newborn rat kidney and in the young and mature adult rat kidney. Dietary sodium depletion increased the density of the AT2 receptor band in mature adult rat kidneys. These data provide evidence that the AT2 receptor protein is expressed in the fetal and newborn rat kidney, diminishes in adult life, and is reexpressed in the adult in response to sodium depletion.