Interactions of angiotensin II and GABA-ergic agents at the threshold of convulsive reactions.

The effects of angiotensin II (AT II), GABA, muscimol (administered i.c.v.) and of amino-oxiacetic acid (AOAA) and baclofen (administered i.p.), as well as of the combinations of AT II with these substances and bicuculline, were studied with respect to the threshold of the convulsive seizures induced by timed intravenous infusion of pentylenetetrazol (PTZ) in mice. It was found in the experiments that the threshold-increasing effect of GABA, muscimol and AOAA was potentiated by AT II (applied in a dose which did not change essentially the convulsive threshold). The potentiated effect of GABA, muscimol and AOAA on the convulsive threshold, when applied in combination with AT II, was antagonized by bicuculline. The threshold-increasing effect of baclofen was not affected substantially by AT II; in this case bicuculline had no effect. On the basis of the results obtained it may be assumed that AT II performs the functions of an antocoid predominantly for the GABA-A receptors in the central nervous system.