Angiotensin II receptors: In the rat brain, the angiotensin II receptor subtype AT2 is heterogeneous and has been subclassified as AT2A (sensitive to guanine nucleotides and DTT) and AT2B (insensitive to guanine nucleotides and DTT). Each subgroup has a specific localization in brain. AT1 and AT2A and AT2B receptors are selectively localized in the rat fetus and their characteristics are similar to those of the adult. Novel sites of localization for AT2B receptors have been found in the deep cerebellar nuclei, the superior sagittal sinus and the cranial nerve nuclei. Both subtypes, AT1 and AT2 angiotensin II receptors, play a role in cerebral blood flow autoregulation. In the rat brain, the median eminence contains exclusively AT1 receptors. These receptors are coupled to PI turnover, but not to the cAMP or cGMP. At a certain age (1 week), the expression of aortic AT2 receptors is enhanced in spontaneously hypertensive rats. In the rat spleen, AT1 receptors are coupled to PI turnover. The adult kidney expressed only AT1 receptors. Conversely, the fetal rat kidney expressed mainly AT2 receptors. High expression of AT2 receptors occurs experimental wound healing in subcutaneous tissues. High expression of AT1 receptors occurs in the aortic neointimal smooth muscle cells formed after balloon angioplasty. In vivo administration of the AT1 antagonist losartan blunts the secretion of ACTH during acute immobilization stress.
