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Aggressive behaviour (muricidal) induced in rats by local electrolyte lesions of septal brain area was accompanied by changes in angiotensin-converting enzyme (ACE) and total kinin-destroying activity (KDA) in different brain regions. In 2-month-old rats (30 days after septal operation) a decrease in ACE activity was observed in hypothalamus and striatum, while in the cerebellum the activity was increased. KDA in this group of aggressive rats was markedly increased in the pituitary body, hypothalamus and striatum. Half a year after septal lesion in spite of aggressive behaviour retention, ACE activity and KDA did not differ from their activity in nonmuricidal rats of the same age. These data show a distinct role of the peptides studied in the formation and maintenance of muricidal behaviour in rats of different age.

The physiological and biochemical activity of new angiotensin converting enzyme inhibitors is studiedin vitro (in microsomal fractions from the pituitary gland and corpus striatum) andin vivo. Compound PP-09, an N-carboxyalkyl derivative of enalapril, displaying high inhibiting activity towards rat serum and tissue angiotensin converting enzyme and lowering arterial pressure in spontaneously hypertensive rats, is selected.