P-299: Angiotensin II (ang II)-induced stimulation of nadph causes a biphasic effect on ERK1/2 in-vivo and in-vitro

We recently found that a 2-week infusion of subpressor doses of Ang II (SP-Ang II) increases pressor responses to simple stimuli without causing sustained hypertension (HTN). Because pressor doses of Ang II (Pres-Ang II) increase NADPH activity, which in turn stimulates ERK1/2, we tested whether SP-Ang II-enhanced pressor responses are associated with increases in NADPH and ERK1/2 (via the AT1 receptor). Sprague-Dawley rats received an i.v. infusion of either SP-Ang II (50 ng/kg/min; n=15), Pres-Ang II (300 ng/kg/min; n=8), or vehicle (saline; n=6) via osmotic minipumps. Eight of the SP-Ang II rats also received losartan (30mg/kg/day po). We measured blood pressure (BP) continuously by telemetry, and tested pressor responses by monitoring BP during tail cuff plethysmography (TCP). On day 13, we harvested the aortas for Western Blot analysis of p47phox (a NADPH subunit) and ERK1/2. As in our previous studies, SP-Ang II enhanced pressor responses (by 24±8 mmHg during TCP) without causing sustained HTN (124±3 vs. 127±5 mmHg). Pres-Ang II increased pressor responses (by 47±20 mmHg) and caused sustained HTN (130±3 vs. 174±15 mmHg). As expected, Ang II caused a dose-dependent increase in p47phox. Interestingly, SP-Ang II decreased ERK1/2, while Pres-Ang II increased it. Losartan prevented the Ang II-induced changes. Because of the dissociation between the effect of Ang II on p47phox and ERK1/2, we hypothesized that Ang II causes a dose dependent increase in NADPH, which in turn has a biphasic effect on ERK1/2: inhibition followed by stimulation. To test this, we incubated aortic rings with increasing doses of Ang II (10-10 to 10-4 M) in the presence and absence of either losartan (10-5M) or a NADPH inhibitor (DPI: 10-4 M). We then measured p47phox and ERK1/2. Ang II caused a dose-dependent increase in p47phox. In contrast, Ang II decreased ERK1/2 at low doses (10-8 M decreased it by 35%), but increased it at high doses (10-4 M increased it by 40%). Losartan prevented Ang II-induced increases in p47phox and the biphasic changes in ERK1/2. The NADPH inhibitor also reversed both the inhibitory and stimulatory effects on ERK1/2. In conclusion, in vivo or in vitro activation of the AT1 receptor by Ang II, progressively increases NADPH activity, which in turn has a biphasic effect on ERK1/2: it inhibits ERK at low levels but stimulates it at higher levels. Am J Hypertens (2004) 17, 141A–142A; doi: 10.1016/j.amjhyper.2004.03.374