Angiotensin-converting enzyme, bradykinin, angiotensin, and cerebral vessel reactivity.

Bradykinin (BK) produced concentration-related relaxations of cat middle cerebral arteries and was ineffective in cat basilar arteries. On rabbit basilar arteries, BK initially produced concentration-related relaxations; however, when repeated at 2-hour intervals, BK eventually produced pure contractile responses. After preincubation of the tissues with cycloheximide, BK produced reproducible relaxation responses. The angiotensin-converting enzyme inhibitors, SQ 14,225, BPP5a, and BPP9a, had no effect on the concentration-effect curves of BK, AII, or 5-HT with any of the preparations, but responses to AI were inhibited. These results suggest that, in these tissues, angiotensin-converting enzyme is important for conversion of AI to AII, but apparently not for the degradation of BK.