Brain angiotensinogen: in vitro synthesis and chromatographic characterization

The capacity of rat brain to synthesize angiotensinogen (renin substrate) was examined in vitro using brain slices (300 micrometers thick) incubated in minimum essential medium (Eagles) at pH 7.4 and 37 degrees C for 2 h. The concentration of angiotensinogen (measured as equivalents of angiotensin I;AI) increased from 5.2 +/- 1.1 ng AI/g of incubated tissue to 40 +/- 4 ng AI/g at 2 h. In the presence of cycloheximide (10 micrograms/ml) or vinblastine sulfate (10 micrograms/ml) the values at the 2 h interval were 24.5 +/- 3.5 ng AI/g and 10.5 +/- 3.5 ng AI/g respectively. The angiotensinogen released by brain slices was pooled and some of its physicochemical properties examined and compared to those of angiotensinogen from plasma and saline-perfused brains. Chromatography on Sephacryl S-200 showed brain and plasma angiotensinogen to be similar in size (mol. wt. approximately 59,000) but large differences in binding activity to Concanavalin A were found. Only 31% of plasma angiotensinogen bound to the affinity medium compared to 63% for the pooled incubation medium. It was concluded that de novo synthesis of angiotensinogen occurs in the rat brain and that the brain protein may differ in its glycoside composition from hepatic angiotensinogen.