Selective local action of angiotensin II on dopaminergic neurons in the rat hypothalamus in vivo.

Microdialysis was used to investigate whether angiotensin II modulates the basal and K+-induced release of endogenous noradrenaline, dopamine and their metabolites 3,4-dihydroxyphenylglycol (DOPEG) and 3,4-dihydroxyphenylacetic acid (DOPAC) from the anterior hypothalamus of the anaesthetized rat. The release of the amines was stimulated twice (ST1 and ST2) with either 50 mmol/l or 100 mmol/l K+. The release of each amine induced by K+ was reproducible and concentration-dependent. Angiotensin II when present in the perfusion fluid after ST1 at a concentration of 0.1 and 10 mumol/l (chosen after in vitro experiments had shown that the recovery of the peptide across the dialysis membrane was only 3.6%), had no significant effect on amine release. However, 10 mumol/l angiotensin II induced an immediate, significant increase in basal DOPAC outflow which reached a maximum of 89% in the 100 mmol/l K+ and 53% in the 50 mmol/l K+ experiments. No such effect was observed with DOPEG outflow. In a separate experimental series, addition of angiotensin II without a preceding K+ stimulation period did not significantly affect the outflow of the amines and metabolites. The results suggest that angiotensin II can selectively influence dopamine metabolism in the anterior hypothalamus in vivo but does not act locally to acutely facilitate the release of endogenous catecholamines from this brain area.