Psychotropic activity of angiotensin II and its fragments Val-Tyr-Ile-NH2 and Val-Tyr-Ile-His-NH2.

Angiotensin II (A II) significantly enhanced the motor activity of rats in the open field as measured by forward locomotion, rearings and bar approaches while the tripeptide [A II(3-5)] and the tetrapeptide [A II(3-6)] were ineffective in this test. Also, the stereotyped behavior produced by apomorphine (2 mg/kg) or amphetamine (6.5 mg/kg), both given intraperitoneally, was significantly more intense in rats receiving an icv injection of A II but not A II(3-5) or A II(3-6). A II significantly increased the rate of acquisition of active avoidance while AII(3-5) and AII(3-6) were ineffective. Finally, a remarkable improvement of performance in the passive avoidance situation was caused by AII, and none by AII(3-5) and AII(3-6). These results show that 3-5 and 3-6 fragments of AII are not responsible for the psychotropic activity of their parent octapeptide and suggest that AII(3-7) pentapeptide should be the fragment in question.