The present study tested the hypothesis that nitric oxide contributes to the impaired baroreflex gain of pregnancy and that this action is enhanced by angiotensin II. To test these hypotheses, we quantified baroreflex control of heart rate in non-pregnant and pregnant conscious rabbits before and after: 1) blockade of nitric oxide synthase (NOS) with N-nitro-L-arginine (20 mg/kg, iv), 2) blockade of the angiotensin II AT₁ receptor with L158-809 (5 µg/kg/min, iv, 3) infusion of angiotensin II (1ng/kg/min non-pregnant, 1.6-4 ng/kg/min pregnant, iv), 4) combined blockade of angiotensin II AT₁ receptors and NOS, and 5) combined infusion of angiotensin II and blockade of NOS. To determine the potential role of brain neuronal NOS (nNOS), mRNA and protein levels were measured in the paraventricular nucleus, nucleus of the solitary tract, caudal ventrolateral medulla and rostral ventrolateral medulla in pregnant and non-pregnant rabbits. The decrease in baroreflex gain observed in pregnant rabbits (from 23.3 ± 3.6 to 7.1 ± 0.9 beats/min/mmHg, P<0.05) was not reversed by NOS blockade (to 8.3±2.5 beats/min/mmHg), angiotensin II blockade (to 5.0±1.1 beats/min/mmHg), or combined blockade (to to 12.3±4.8 beats/min/mmHg). Angiotensin II infusion with (to 5.7±1.0 beats/min/mmHg) or without (to 8.4±2.4 beats/min/mmHg) NOS blockade also failed to improve baroreflex gain in either group. In addition, nNOS mRNA and protein levels in cardiovascular brain regions were not different between nonpregnant and pregnant rabbits. Therefore, we conclude that nitric oxide, either alone or via an interaction with angiotensin II, is not responsible for the decrease in baroreflex gain during pregnancy.