The Angiotensin Type 1 and Type 2 Receptor Families

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Abstract
Angiotensin II (AngII) is one of the key hormones involved in the regulation of cardiovascular and body fluid homeostasis. Several naturally occurring stimuli such as hypovolemia, hyponatremia and hypotension are well known to activate the renin-angiotensin system (RAS) (cf. (1)). The rate-limiting step in the synthesis of AngII is the release of renin from the juxtaglomerular cells of the kidney. Renin converts the plasma α-globulin protein angiotensinogen to AngI, which subsequently is converted to AngII by a carboxyl dipeptidase known as angiotensin converting enzyme. AngII has numerous peripheral target organs and actions including vasoconstriction, aldosterone release, and augmentation of sympathetic nervous system function. Circulating AngII also has important central nervous system (CNS) effects although, like the other peptide hormones, it has restricted access to most cerebral structures because of the blood-brain barrier. However, by acting on the circumventricular organs (CVOs) that possess fenestrated capillaries, blood-borne AngII can act centrally to regulate pituitary function, elicit a central pressor response that likely involves descending activation of the sympathetic nervous system, and stimulate thirst and salt appetite (cf. (2)). In addition to the well-established peripheral RAS, AngII and related smaller peptides also can be directly generated in the CNS where the peptide appears to participate in the regulation of cerebral blood flow, neurohypophysial hormone release, and in the pathophysiology of some forms of hypertension (2–4).

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