ABSTRACT
The early work of Frey and Werle in the 1920s and 1930s revealed the presence of a hypotensive factor, which they called kallikrein, in urine, blood, pancreas, and salivary glands. In the late 1930s, Werle and colleagues characterized this factor as an enzyme that released an active component from a blood-borne precursor which then gradually disappeared. They called the active decapeptide “kallidin”, while Rocha e Silva named the nonapeptide released from plasma kininogen “bradykinin” (Bk). A second Bk-degrading enzyme in blood and kidney was discovered soon after and named kininase II, which was later shown to be identical with the angiotensin-converting enzyme (ACE). The potentiation of Bk effects by ACE inhibitors appears to go beyond protecting Bk against breakdown by ACE, because it is not necessarily due to inhibition of enzymatic inactivation alone.
