Angiotensin Converting Enzyme Activity in Brain Microvessels of Rats

Abstract

Angiotensin converting enzyme (ACE) is a carboxyl terminal dipeptidyl dipeptidase, which is known to convert angiotensin I to angiotensin II (Ang II) and to hydrolyze bradykinin and enkephalin. In the brain, ACE is located in endothelial cells of capillaries throughout the brain, in the subfornical organ, and in the brush border of choroidal epithelial cells in contact with cerebrospinal fluid [1]. Administration of Ang II into the brain ventricles induces thirst [2], a rise in arterial blood pressure, and secretion of vasopressin [3]. Recently, the specific binding of Ang II to the membrane fraction of canine brain microvessels was detected, suggesting the role of Ang II in regulation of the brain microcirculation and transport across the blood-brain barrier [4]. Since ACE in the brain microvessels might affect the brain microcirculation by modulating the local production of Ang II, we measured ACE activity in brain microvessels obtained from 13-week-old spontaneously hypertensive rats (SHR), Wistar-Kyoto rats, and SHR of the same age under antihypertensive therapy to clarify the effect of hypertension on the brain microvessels.