Tissue distribution of angiotensinogen mRNA during experimental inflammation

It has been proposed that angiotensinogen is an acute phase protein, because its plasma concentrations increase during some forms of acute inflammation. However, this is not a consistent finding. Furthermore, no specific function of circulating angiotensinogen in the inflammatory reaction is known. This may be different for extrahepatic synthesis of angiotensinogen, as the local generation of angiotensin II has been implicated in inflammation-related processes in some organs. We have therefore examined the expression of the angiotensinogen gene in liver and extrahepatic tissues under the influence of experimental inflammatory stimuli in comparison to the effects of dexamethasone. Dexamethasone (7 mg/kg intraperitoneally) induced a several-fold increase in angiotensinogen mRNA in liver, aorta, heart, adrenal, and a moderate increase in kidney, testis, and brain. Plasma concentrations of angiotensinogen, alpha 1-acid glycoprotein, and alpha 2-macroglobulin increased, whereas albumin concentrations decreased. Lipopolysaccharide (500 micrograms/kg subcutaneously) stimulated angiotensinogen mRNA in hepatic, cardiac, renal, adrenal, and testicular tissues, but not in the brain. Plasma concentrations of angiotensinogen, alpha 1-acid glycoprotein, and alpha 2-macroglobulin increased, those of albumin decreased. In turpentine-treated rats (5 ml/kg subcutaneously), angiotensinogen mRNA was reduced in liver and kidney; stimulated in adrenals, testis, and heart; and not influenced in the brain. Plasma concentrations of the acute phase proteins increased, whereas angiotensinogen and albumin decreased. It is concluded that hepatic and extrahepatic angiotensinogen gene expression seem to be regulated similarly by dexamethasone and lipopolysaccharide. The different response to turpentine may reflect differences in the pattern of cytokines induced by turpentine or be associated with additional pharmacological effects of turpentine or its metabolites.