Mitogen-Activated Protein Kinases Mediate Upregulation of Hypothalamic Angiotensin II Type 1 Receptors in Heart Failure Rats

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Abstract
In heart failure (HF), angiotensin II type 1 receptor (AT 1 -R) expression is upregulated in brain regions regulating sympathetic drive, blood pressure, and body fluid homeostasis. However, the mechanism by which brain AT 1 -R are upregulated in HF remains unknown. The present study examined the hypothesis that the angiotensin II (Ang II)–triggered mitogen-activated protein kinases (MAPKs) p44/42, p38, and c-Jun N-terminal kinase contribute to upregulation of the AT 1 -R in the hypothalamus of rats with HF. AT 1 -R protein, AT 1 -R mRNA, and AT 1 -R immunoreactivity increased in the paraventricular nucleus of hypothalamus and the subfornical organ of rats with ischemia-induced HF compared with sham-operated controls. Phosphorylated p44/42 MAPK, c-Jun N-terminal kinase, and p38 MAPK also increased in paraventricular nucleus and subfornical organ. A 4-week ICV infusion of the AT 1 -R antagonist losartan decreased AT 1 -R protein and phosphorylation of p44/42 MAPK, c-Jun N-terminal kinase, and p38 MAPK in the HF rats. A 4-week ICV infusion of the p44/42 MAPK inhibitor PD98059 or the c-Jun N-terminal kinase inhibitor SP600125 significantly decreased AT 1 -R protein and AT 1 -R immunoreactivity in the paraventricular nucleus and subfornical organ, but the p38 MAPK inhibitor SB203580 did not. Treatment with ICV losartan, PD98059, and SP600125 had no effect on AT 1 -R expression by Western blot in sham-operated rats. In untreated HF rats 4 weeks after coronary ligation, a 3-hour ICV infusion of PD98059, SP600125, or losartan reduced AT 1 -R mRNA in paraventricular nucleus and subfornical organ. These data indicate that MAPK plays an important role in the upregulation of AT 1 -R in the rat forebrain in HF and suggest that Ang II upregulates its own receptor by this mechanism.

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