Angiotensin II concentration in cerebrospinal fluid after intraventricular injection of angiotensinogen or renin.

To determine if the brain enzyme which has renin-like activity in vitro can form angiotensin in vivo, angiotensin II concentration in cerebrospinal fluid (CSF) was measured before and at various intervals after injection of partially purified renin substrate (angiotensinogen) into the third cerebral ventricle of anesthetized dogs. The injection increased CSF angiotensinogen concentration 3-fold, but despite this, CSF angiotensin II concentration, which was undetectable (less than 6.25 fmol/ml) before injection, did not change. Arterial blood pressure was also unchanged after the injection. In contrast, both CSF angiotensin II concentration and arterial pressure increased after an inventricular injection of renin. These results demonstrate that angiotensin II is formed centrally after administration of exogenous renin but not after injection of angiotensinogen. The results thus fail to demonstrate renin activity in the brain in vivo.