Angiotensin II AT 2 Receptor Stimulation Extends the Upper Limit of Cerebral Blood Flow Autoregulation: Agonist Effects of CGP 42112 and PD 123319

The effects of the angiotensin II AT₂ receptor ligands CGP 42112 and PD 123319, the AT₁ antagonist losartan, and the nonselective angiotensin II antagonist Sar¹,Ile⁸-angiotensin II on the upper limit of CBF autoregulation were studied in pentobarbital-anesthetized rats. Blood pressure was increased by intravenous phenylephrine infusion, while CBF was measured continuously from the parietal cortex by laser–Doppler flowmetry. Intravenous infusions of CGP 42112 (0.1 and 1 mg kg⁻¹ min⁻¹) and PD 123319 (0.36 and 1 mg kg⁻¹ min⁻¹) shifted the upper limit of CBF autoregulation toward higher blood pressures without affecting baseline CBF. Sar¹,Ile⁸-angiotensin II (4 μg kg⁻¹ min⁻¹) had no effect on baseline CBF or CBF autoregulation but antagonized the effect of CGP 42112 and PD 123319. Losartan (10 mg/kg i.v. bolus) reduced baseline blood pressure and CBF and shifted the autoregulation curve toward higher blood pressures. Sar¹,Ile⁸-angiotensin II blocked the effect of losartan on baseline CBF but not on CBF autoregulation. These results suggest that both CGP 42112 and PD 123319 exert their effects on CBF autoregulation through stimulation of angiotensin II AT₂ receptors. The mechanism by which losartan affects CBF remains unclear.