Distribution of angiotensin-converting enzyme activity in specific areas of the rat brain stem.

Angiotensin-converting enzyme (ACE) activity was measured by a radiochemical assay in 30 specific areas of the rat brain stem. ACE activity is unevenly distributed, with a 60-fold difference between the lowest and the highest activity. The area postrema exhibits the highest activity. The substantia nigra (pars reticulata), the locus coeruleus, the areas A1 and A2, the nuclei commissuralis, and tractus solitarii have a substantial ACE activity, whereas the lowest activity is found in the raphe nuclei and the nuclei of the reticular formation.