Lack of Cross Talk Between α1-Adrenergic and Angiotensin Type 1 Receptors in Neurons of Spontaneously Hypertensive Rat Brain

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Abstract
Norepinephrine causes downregulation of angiotensin II (Ang II) receptors in Wistar-Kyoto rat (WKY) brain neuronal cultures. The aim of this study was to compare the cross talk between Ang II and α1-adrenergic receptors in these neuronal cultures. Norepinephrine causes a 66% decrease in Bmax of Ang II type 1 (AT1) receptors in neuronal cultures of WKY brain. This decrease is mediated by the interaction of norepinephrine with the α1A-adrenergic receptor subtype. Norepinephrine also causes a decrease in mRNA levels for AT1 receptors. A maximal decrease of 83% in AT1 receptor mRNA is observed in 8 hours with 100 μmol/L norepinephrine, is blocked by 5-methyluradipil, and involves inhibition of AT1 receptor transcription. Furthermore, decreases in the AT1 receptor and its mRNA are associated with a significant attenuation of AT1 receptor–mediated stimulation of norepinephrine transporter mRNA in WKY brain neurons. In contrast, norepinephrine does not decrease AT1 receptors or mRNA and has no effect on...