Differential influence of iNOS and nNOS inhibitors on rostral ventrolateral medullary mediated cardiovascular control in conscious rats.

We evaluated the cardiovascular effects of nitric oxide (NO) inhibitors microinjected into the rostral ventrolateral medulla (RVLM) of conscious rats. Application of L-NAME or aminoguanidine (AG) induced an increase in arterial blood pressure (MAP) and an increase in heart rate, whereas 7-nitroindazole (7-NI) decreased MAP and HR. Microinjection of glutamate produced an increase in MAP which was followed by either a tachycardia or a bradycardia. Such responses were blocked totally by prior administration of L-NAME and attenuated (approximately 50%) by 7-NI. In contrast, glutamate responses were enhanced by following AG. We conclude that in conscious rats, NO has tonic effects in the RVLM and may participate in the modulation of the actions of glutamate through iNOS and nNOS pathways.