Angiotensin II receptors: Angiotensin II regulates cerebral blood flow through AT2 receptors. The selective ligands PD 123319 and CGP 42112 act as agonists and shift the autoregulation curves towards higher blood pressures. Administration of PD 123319 improves survival in the gerbil model of stroke. Cerebrovascular AT2 receptors reduce cGMP, and their stimulation constricts the isolated rat basilar artery. Angiotensin (3-8) (angiotensin IV) administration improves cerebrovascular flow after hemorrhage. A new radioligand, [125I]CGP 42112, has been used to quantify and characterize brain AT2 receptors. AT1 and AT2 receptors in the visual system (superior colliculus) are modulated by the optic nerve afferents. After denervation, the expression of AT2 is decreased, and that of AT1 receptors is increased. AT2 receptors have been purified to homogeneity from the neonatal rat kidney by solubilization, gel filtration, affinity chromatography. After balloon-injury of the carotid and aorta, high expression of AT1 receptors is restricted to the proliferating cells in the neointima. Reproductive hormones (estrogen-progesterone) regulate the expression of AT1 receptors in the dorsal arcuate nucleus. AT1 receptors are highly express in mice breast tumors of ductal origin, whereas AT2 receptors associate with connective tissue in tumors of lobular origin. Immature kidney glomeruli express AT2 receptors; fully functional, vascular glomeruli express AT1 receptors. Other receptors: Binding to melatonin receptors in rat cerebral arteries is sensitive to guanine nucleotides. Stimulation of these receptors inhibits CAMP production. Endothelin receptor expression is enhanced in carotid artery after balloon injury.
