Proteolytic conversion of angiotensins in rat brain tissue

The proteolytic conversion of angiotensins in rab brain preparations was studied. Angiotensin I was converted into angiotensin II by enzymes which were associated with a synaptic membrane preparation, while angiotensin II was relatively resistant to proteolysis by these enzymes. Angiotensin II was rapidly metabolized at both pH 7.4 and pH 5.4 by enzymes in the soluble fraction of a synaptosomal preparation. One of the fragments formed at pH 7.4 was characterized as angiotensin III. At pH 5.4 only one fragment was generated which was characterized as angiotensin-(1-7)-heptapeptide. Enzymatically generated angiotensin II and III displayed pronounced biological activity in the brain, whereas angiotensin-(1-7)-heptapeptide was inactive. These data indicate a route for the generation, and the inactivation of biologically active angiotensins in the brain.