Differential actions of angiotensin II and angiotensin-(1-7) on transmitter release

The central cardiovascular and dipsogenic effects of angiotensin II involve interactions with norepinephrine, dopamine, and serotonin. Our findings that angiotensin II receptors and substance P immunoreactivity show a parallel distribution in the dorsal medulla and that angiotensin II releases substance P from perfused rat medulla slices revealed the potential for a functional relation between these peptidergic systems as well. Additional evidence suggests that the heptapeptide angiotensin-(1-7) exerts its biological activities via selective angiotensin receptor subtypes. Thus, we compared the effects of these two peptides on release of substance P and monoamines in perfused slices of medulla and hypothalamus from 77 male Sprague-Dawley rats. Transmitter levels were determined in 6-minute collections of perfusate before (basal), during (experimental), and after (recovery) perfusion with either angiotensin-(1-7), angiotensin II, or Krebs' solution alone (control). Substance P was measured by radioimmunoassay and monoamines and their metabolites by high-performance liquid chromatography with electrochemical detection. In the medulla, 2 microM angiotensin II but not angiotensin-(1-7) significantly increased efflux of substance P (221 +/- 87% of basal) and norepinephrine (130 +/- 17% of basal) during the experimental period. The effect of angiotensin II on substance P was sustained into the recovery period. Dopamine and its metabolite 3,4-dihydroxyphenylacetic acid were not detected in this brain region. In the hypothalamus, both angiotensin-(1-7) and angiotensin II increased substance P (169 +/- 30% and 141 +/- 35% of basal, respectively); the effect of angiotensin II was sustained throughout the recovery period.(ABSTRACT TRUNCATED AT 250 WORDS)