Angiotensin-converting enzyme in macro- and microvessels of the rat.

1. Angiotensin-converting enzyme (ACE) was measured in the aorta, cerebral and mesenteric microvessels of Wistar-Kyoto rats using a specific radioligand assay. 2. Ligand binding studies revealed a four-fold increase in concentration of ACE in mesenteric microvessels, compared with aorta or brain microvessels. The dissociation constant (Kd) was similar in all tissues. 3. The effects of oral administration of the ACE inhibitor S9650 on vascular ACE in vivo were measured. 4. S9650 produced a dose-dependent inhibition of vascular ACE from brain and mesenteric microvessels.