Interactions between the renin-angiotensin system and the brain

Changes of plasma renin activity by intracerebroventricular administration of biological active peptides in conscious rats

We studied the effects of intracerebroventricular administration of angiotensin II (ANG II), bradykinin (BK), leucine-enkephalin (Leu-ENK) and neurotensin (NT) on plasma renin activity (PRA), blood pressure and heart rate in conscious and unrestrained rats. Five microliters of each peptide solution was injected into the lateral cerebral ventricle. These four peptides all produced pressor effects after intracerebroventricular injection. ANG II and NT significantly suppressed PRA, BK did not affect PRA, and Leu-ENK significantly increased PRA. The central peptidergic stimulation caused by these four peptides increased blood pressures in conscious rats but showed different effects on PRA.

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.