Vascular _2B-adrenoceptors (_2B-AR) may mediate vasoconstriction and contribute to the development of hypertension. Therefore we hypothesized that blood pressure would not increase as much in mice with mutated _2B-AR as in wild type (WT) mice following nitric oxide synthase (NOS) inhibition with N--nitro-L arginine (L-NNA, 250 mg/L in drinking water). Mean arterial pressure (MAP) was recorded in heterozygous (HET) _2B-AR knockout mice and WT littermates using telemetry devices for 7 control and 14 L-NNA treatment days. MAP in HET mice was increased significantly on treatment days 1 and 4 to 14 while MAP did not change in WT mice (days 0 and 14 = 113±3 and 114±4 mmHg in WT, 108±0.3 and 135±13 mmHg in HET, p < 0.05). MAP was significantly higher in HET than in WT mice days 10 through 14 (p<0.05). Thus mice with decreased _2B-AR expression became more hypertensive rather than less following NOS-inhibition. We therefore examined constrictor responses to phenylephrine (PE, 10-9 to 10-4 M) with and without NOS-inhibition to determine basal NO contributions to arterial tone. In small pressurized mesenteric arteries (inner diameter = 177 ±5 µm), PE constriction was decreased in untreated HET arteries compared to WT (p< 0.05). L-NNA (100 µM) augmented PE constriction more in HET than in WT arteries and responses were not different between groups in the presence of L-NNA. Acetylcholine dilated preconstricted arteries from HET mice more than arteries from WT mice. Endothelial NOS (eNOS) expression was increased in HET compared to WT mesenteric arteries by Western analysis. Griess assay showed increased NOx concentrations in HET plasma compared to WT. These data demonstrate that diminished _2B-AR expression increases the dependence of arterial pressure and vascular tone on NO production and that vascular _2B-AR either directly or indirectly regulate vascular endothelial NOS function.