A, effect of the nonselective NOS inhibitor l-NAME (10 mg/kg i.v.) or induction by PE infusion (2.7 μg/kg/min; 18 μl/min) of a comparable elevation in mean arterial pressure to that caused by l-NAME, on the pressor responses elicited by NMDA (125, 250, 500, or 1000 μg/kg i.v.). *, P < 0.05 versus l-NAME + NMDA. B, intravenous saline (vehicle for NMDA) was injected after l-NAME or phenylephrine administration. C and D, effect of pretreatment, 30 min earlier, with the selective nNOS inhibitor NPLA (150 μg/kg i.p.) (C) or the selective eNOS inhibitor l-NIO (4 or 10 mg/kg i.v.) (D) on the dose-pressor response curve elicited by intravenous NMDA. The vehicle for l-NIO and NPLA (saline) was administered as a control before NMDA. In C, *, p < 0.05 versus saline pretreatment group. Values are means ± S.E.M. of four to six observations.