The octapeptide angiotensin II (AII) is a well-known circulating hormone. Its generation in the blood involves a cascade in which the kidney enzyme renin cleaves angiotensinogen (secreted by the liver) into angiotensin I (AI). Converting enzyme then converts AI and AII. The main action of circulating AII is to increase vascular tone and promote salt and water retention. However, in addition to this system which produces the majority of circulating AII, many endocrine organs have been shown to contain renin and generate AII locally. Previous reports support the hypothesis that locally-generated AII may have paracrine effects in these organs. Nonetheless, much more work is needed to understand (1) what is the exact physiological importance of locally-generated AII; (2) which factors regulate the local production of AII; (3) what is the exact biochemical pathway leading to the local generation of AII. In the proposed study, we will address these questions in three endocrine organs where there is strong evidence for local renin- angiotensin systems (RAS), namely, the anterior pituitary gland, the adrenal cortex and the testicular Leydig cells in the rat. We have developed the appropriate techniques that enable us to (1) detect AII in tissues by immunocytochemistry, radioimmunoassay and HPLC; (2) detect renin in tissues by immunocytochemistry and enzymatic assay; (3) detect angiotensinogen in tissues by immunocytochemistry and enzymatic assay; (4) detect renin or angiotensinogen mRNA's in tissues, by in situ hybridization histochemistry. By combining the techniques, we will seek to determine which components of the RAS are present (or absent) in these tissues, where they are located and how they interact. In order to understand what regulates the local production of AII, we will determine the effect of various conditions on the concentration of AII, renin, angiotensinogen and their respective messenger RNA's in these endocrine organs. Finally, we will seek to determine whether various Leydig cell lines can be used as an experimental model to study the intracellular generation of AII.
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