ANGIOTENSIN-II REGULATION OF TYROSINE-HYDROXYLASE GENE-EXPRESSION IN THE NEURONAL CULTURES OF NORMOTENSIVE AND SPONTANEOUSLY HYPERTENSIVE RATS

In the present study we investigated the regulation of tyrosine hydrox ylase (TH) by angiotensin a (Aug II) in an attempt to provide cellular and molecular evidence that this hormone has increased neuromodulator y actions in the spontaneously hypertensive (SH) rat brain. Neuronal c ells in primary culture from the hypothalamus-brain stem of both normo tensive [Wistar-Kyoto (WKY)] and SI-I rats have been used. These cultu re mimic in vivo situations. Ang I-I caused a time-dependent increase in TH activity in WKY rat brain neurons. A maximal increase of 2.5-fol d was observed with 100 nM Ang II in an actinomycin- and cycloheximide -dependent process. In addition, Ang II caused a parallel increase in TH messenger RNA (mRNA) levels, with a maximal stimulation of 5-fold i n 4 h by 100 nM Ang II in WKY rat brain neurons. The stimulation of TH mRNA was mediated by the AT, receptor subtype, resulted from an incre ase in its transcription, and involved activation of phospholipase C a nd protein kinase C. Antisense oligonucleotide for c-fos attenuated An g II stimulation of TH mRNA in a time- and dose-dependent fashion, ind icating an involvement of c-fos as a putative third messenger in Ang I I stimulation of TH. Ang II also caused stimulation of TH activity and its mRNA levels in neuronal cultures of SH rat brain by a mechanism s imilar to that observed for neuronal cultures of WKY rat brain, involv ing AT(1) receptors, protein kinase C, and c-fos. However, the stimula tion of TI-I activity and that of TH mRNA were similar to 30% and 80% higher, respectively, in the SH rat br ain neurons than those in the W KY rat brain neurons. In vivo experiments have been carried out to val idate the elevated response of TH gene expression to Ang II in SH rat brain neuronal cultures. Ang II stimulated both TW activity and TH mRN A levels in the hypothalami and brain stems of adult WKY and SH rats. The level of stimulation in the bl ain of the SH rat was significantly higher than that in the WKY rat. These observations are consistent wi th an increase in AT(1) receptor gene expression and suggest that incr eased TH gene expression could be the cellular/molecular basis for the greater neuromodulatory action of Ang II in the SH rat brain.