Angiotensin-(1-7) Elicits a Long-Term Effect on Norepinephrine Neuronal Uptake in Spontaneously Hypertensive Rats: 5c.07

Objective: Sympathetic overactivity, a primary contributor to hypertension development, results from an increase in synaptically released neurotransmitters. We have previously shown that angiotensin (Ang) (1-7), an antihypertensive component of the renin-angiotensin system, decreases norepinephrine (NE) release. Since this effect may be correlated with an augmented NE removal from the synaptic cleft our aim was to investigate the effect of Ang-(1-7) on neuronal NE uptake and NE transporter (NET) expression in spontaneously hypertensive rats (SHR). Design and Method: 3H-NE neuronal uptake was measured in isolated hypothalami incubated with 3H-NE in the absence and presence of Ang-(1-7) during 5 min or 3 h. NET expression was evaluated in hypothalamic neuronal cultures by Western-blot. Results: Hypothalami incubated with 0.1 to 1 μM Ang-(1–7) during 5 min showed no changes in NE neuronal uptake. Conversely, 0.1 μM Ang-(1-7) caused an increase in NET expression after 3 and 5 h incubation (40 ± 7% and 30 ± 9%, respectively) in hypothalamic neuronal cultures from SHR. This effect was blocked by a Mas receptor antagonist and not by an AT1 or AT2 receptor antagonist, suggesting the involvement of Mas receptors. The phosphoinositide 3-kinase (PI3-kinase) inhibitor LY294002 blocked the Ang-(1-7)-stimulated NET expression, suggesting that the PI3K/Akt pathway is involved. In fact, Ang-(1-7) induced Akt phosphorylation. 1 μM actinomycin-D as well as 1 μM cycloheximide blocked the Ang-(1-7)-stimulated NET expression, suggesting that Ang-(1-7) stimulates NET gene transcription and translation. In this way, Ang-(1-7) may elicit a long-term effect on NE neuronal uptake. To test this, the effect of Ang-(1-7) on NE neuronal uptake was evaluated after 3 h incubation. In this condition, Ang-(1-7) increased NE neuronal uptake, and this effect was blocked by the gene translation inhibitor cycloheximide. Conclusions: Ang-(1-7) does not evoke an acute effect on neuronal NE uptake, but induces a long-term effect by increasing NET expression. This effect is coupled to Mas receptor activation through the PI3K/Akt pathway and may involve stimulation of NET gene transcription and translation.