Regulation of norepinephrine transport system by angiotensin II in neuronal cultures of normotensive and spontaneously hypertensive rat brains

Brain angiotensin II (Ang II) plays a key role in blood pressure control in part by interacting with catecholamines (CA) and by stimulation of sympathetic pathways. The significance of Ang-CA interaction is further heightened by the presence of a hyperactive brain Ang II system in spontaneously hypertensive (SH) rat, a genetic model for essential hypertension. Neuronal cells in primary culture from the hypothalamus-brainstem that mimic in vivo situations in so far as many cellular actions of Ang II are concerned, have been used in the present study to elucidate Ang II regulation of CA by determining its cellular action on the norepinephrine transporter (NET) system. Ang II causes both acute and chronic stimulation of [H-3]-norepinephrine (NE) uptake in neuronal cultures of Wistar Kyoto (WKY) rat brain. Acute stimulation begins as early as 5 min, reaches maximal levels in about 30 min in the presence of 100 nM Ang II, and is blocked by losartan, a specific antagonist for AT(1) receptor subtype. In addition, this acute stimulation appears to be a posttranscriptional event and does not involve protein kinase C (PKC) or NET gene transcription. Chronic stimulation of [H-3]-NE uptake by Ang II persists throughout the duration of Ang II incubation (24 h), is dose dependent, and is also mediated by AT(1) receptor subtype. However, chronic stimulation of [H-3]-NE uptake involves PKC, cfos, and NET gene transcription. Ang II also stimulates [H-3]-NE uptake in neuronal cultures of SH rat brain, both acutely and chronically, by mechanisms similar to those observed in neuronal cultures of WKY rat brain. The stimulation of NET by Ang II is 8-fold higher than that seen in WKY and is consistent with increased AT(1) receptor gene transcription and increased functional AT(1) receptors in SH rat brain neurons compared with WKY rat brain neurons. The Ang II stimulation of the NET system is also higher in adult SH compared with WKY rats in vivo. These observations show that 1) Ang II stimulates the NET system both acutely and chronically, the former involving activation of preexisting transporters and the latter involving NET gene transcription and translation; and 2) Ang II stimulation of the NET system is elevated in SH rat brain neurons.