Immunological analysis of angiotensin AT2 receptors in peripheral tissues of neonatal and adult rats.

The peptide hormone angiotensin II (Ang II) is an important regulator of cardiovascular and body fluid homeostasis. Circulating Ang II mediates its physiological actions by activating Ang II receptors in both the periphery and the brain. Previous studies have demonstrated that Ang II receptor expression is high in neonates and decreases to adult levels as the animal matures. A greater proportion of this decline is due to reduced expression of the Type 2 (AT2) receptor subtype. In order to further investigate the expression of this receptor subtype, AT2-directed antisera were utilized to determine the expression of AT2 receptors in both neonatal and adult rat peripheral tissues by immunoblot analysis. The pattern of AT2 receptor immunoreactivity was largely consistent with previous studies employing autoradiographic and radioligand binding assays in peripheral tissues. However, AT2 receptor immunoreactivity was not seen in the adrenal, despite earlier reports of AT2 receptor expression in this peripheral tissue. These immunohistochemical studies also suggested that AT2 receptors undergo tissue-specific post-translational processing during development. Collectively, these results identify immunoreactive AT2 receptor populations in neonatal and adult rat peripheral tissues and further strengthen the hypothesis of AT2 receptor heterogeneity.