Central nitric oxide donors attenuate cardiovascular and central norepinephrine responses to stress

An earlier study showed that norepinephrine (NE) was released in the paraventricular nucleus (PVN) and posterior hypothalamus (PH) along with increases of mean arterial pressure (MAP) and heart rate (HR) during shaker stress (SS). Here we investigated the possibility that nitric oxide (NO) donors, infused into hypothalamus, could modulate responses to SS. In conscious rats, an injector-microdialysis probe, for direct application of donor and collection of extracellular NE, respectively, was inserted into PVN or PH; MAP and HR were recorded continuously from conscious rats. The NO donor, molsidomine (Mel), infused 5 or 30 min before SS, did not alter baseline values of NE, MAP, or HR, but did attenuate changes elicited by 5 min of SS; methylene blue blocked the effects of Mel. The NO donor, sodium nitroprusside, was much less effective than Mol as a modulator of stress-related effects. The results indicate that MAP, HR, and hypothalamic NE responses to environmental stress, but not baseline values, can be modulated by NO donors in the hypothalamus.