Antagonism by neuro-amino acids of the central effects of angiotensin II and renin in rats was investigated. Angiotensin II (100 ng), injected into the preoptic area, stimulated the intake of water but not salt, to a lesser extent and with a shorter duration as compared with that induced by renin (5 mU), injected into the preoptic area. This angiotensin II-induced intake of water was markedly inhibited by [Sar1, Ile8]-angiotensin II, an angiotensin II receptor antagonist, but not by captopril, an angiotensin-converting enzyme inhibitor, previously administered through the same cannula. The angiotensin II-induced intake of water was also inhibited in a dose-dependent manner by gamma-aminobutyric acid (GABA) (50-100 micrograms), muscimol, a GABA agonist, (100-200 ng), taurine (100-200 micrograms) and hypotaurine (100-200 micrograms), administered into the cerebroventricle and by GABA (5-10 micrograms), muscimol (10-20 ng) and taurine (10-20 micrograms) injected into the preoptic area in smaller doses. Renin (5 mU), injected into the preoptic area, elicited a marked increase in the intake of water and salt, which lasted for about 3 days. The effect of renin was inhibited by [Sar1, Ile8]-angiotensin II (10 micrograms) and was eliminated by captopril (25 micrograms) injected into the preoptic area. This effect of renin was not influenced by the peripheral administration of captopril. The effect of renin was also inhibited by GABA, muscimol or taurine injected into the cerebroventricle, in larger doses, or into the preoptic area in smaller doses.(ABSTRACT TRUNCATED AT 250 WORDS)