Immunohistochemical Localization ofAT1a,AT1b, andAT2Angiotensin II Receptor Subtypes in the Rat Adrenal, Pituitary, and Brain with a Perspective Commentary

Abstract

Angiotensin II increases blood pressure and stimulates thirst and sodium appetite in the brain. It also stimulates secretion of aldosterone from the adrenal zona glomerulosa and epinephrine from the adrenal medulla. The rat has 3 subtypes of angiotensin II receptors:AT1a,AT1b, and AT2. mRNAs for all three subtypes occur in the adrenal and brain. To immunohistochemically differentiate these receptor subtypes, rabbits were immunized with C-terminal fragments of these subtypes to generate receptor subtype-specific antibodies. Immunofluorescence revealedAT1aand AT2receptors in adrenal zona glomerulosa and medulla.AT1bimmunofluorescence was present in the zona glomerulosa, but not the medulla. Ultrastructural immunogold labeling for theAT1areceptor in glomerulosa and medullary cells localized it to plasma membrane, endocytic vesicles, multivesicular bodies, and the nucleus.AT1band AT2, but notAT1a, immunofluorescence was observed in the anterior pituitary. Stellate cells wereAT1bpositive while ovoid cells were AT2positive. In the brain, neurons wereAT1a,AT1b, and AT2positive, but glia was onlyAT1bpositive. Highest levels ofAT1a,AT1b, and AT2receptor immunofluorescence were in the subfornical organ, median eminence, area postrema, paraventricular nucleus, and solitary tract nucleus. These studies complement those employing different techniques to characterize Ang II receptors.