ANGIOTENSIN-II-INDUCED NORADRENALINE RELEASE FROM ANTERIOR HYPOTHALAMUS IN CONSCIOUS RATS - A BRAIN MICRODIALYSIS STUDY

Interaction with aminergic transmitter substances has been implicated in the central actions of angiotensin II (ANG II). We used the novel technique of brain microdialysis in conscious rats to investigate whether ANG II influences the release of endogenous catecholamines (CA) from the anterior hypothalamus (AH). Intracerebroventricular (i.c.v.) administration of ANG II (1 ng and 100 ng) increased mean arterial pressure. ANG II at 1 ng had no effect on the release of noradrenaline (NA) from the AH but ANG II at 100 ng significantly increased NA release. Intracerebroventricular pretreatment with the ANG II-receptor antagonist sarilesin (Sar1, Ile8-ANG II; 3-mu-g) prevented the ANG II-induced NA release. The release of the intraneuronal NA and dopamine (DA) metabolites 3,4-dihydroxphenylethyl glycol (DOPEG) and 3,4-dihydroxyphenylacetic acid (DOPAC) from the AH was not altered by i.c.v. ANG II. Our results provide the first in vivo evidence for NA release from the hypothalamus induced by periventricular ANG II receptor stimulation. They support the hypothesis that hypothalamic noradrenergic mechanisms are involved in the central actions of this peptide.