Comparative studies on the central effects of angiotensin II and of its fragments.

Comparative studies were carried out of the central effects of the octapeptide angiotensin II (AT II) and of its fragments: C-terminal hexapeptide (AT 3-8), middle tetrapeptide (AT 3-6) and initial tripeptide (AT 1-3). The experiments were carried out with respect to the cerebral level of the biogenic amines DA, NA, 5-HT and their metabolites HVA and 5-HIAA in intact mice and in mice pretreated with haloperidol, as well as with respect to the animals' behaviour (haloperidol catalepsy, apomorphine stereotypy, unconditioned jumping reaction, hexobarbital sleep and the threshold of convulsive seizures induced by times intravenous infusion of pentylenetetrazol). The fragments studied were found to manifest activity in the tests used. In some respects this activity is very similar to the activity of AT II. There are also effects which differ from those of AT II, as well as effects which are entirely opposite in some respects, which makes it possible to examine some of these substance as its potential natural antagonists. All this shows that the biological activity of AT II in the brain undergoes a number of qualitative and quantitative changes when its molecule broken to produce peptides with shorter chains. In the effects observed AT II and its fragments interact predominantly with the DA-ergic transmission in the brain.