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Cardoso LM, Colombari DS, Menani JV, Toney GM, Chianca DA Jr, Colombari E: Cardiovascular responses to hydrogen peroxide into the nucleus tractus solitarius. Am J Physiol Regul Integr Comp Physiol. 2009 Aug;297(2):R462-9. Epub 2009 Jun 10.
The nucleus tractus solitarius (NTS), a major hindbrain area involved in cardiovascular regulation, receives primary afferent fibers from peripheral baroreceptors and chemoreceptors. Hydrogen peroxide (H (2) O (2)) is a relatively stable and diffusible reactive oxygen species (ROS), which acting centrally, may affect neural mechanisms. In the present study, we investigated effects of H (2) O (2) alone or combined with the glutamatergic antagonist kynurenate into the NTS on mean arterial pressure (MAP) and heart rate (HR). Conscious or anesthetized (urethane and alpha-chloralose) male Holtzman rats (280-320 g) were used. Injections of H (2) O (2) (125 to 1500 pmol/40 nl) into the intermediate NTS of anesthetized rats evoked dose-dependent and transient hypotension (-18 +/- 3 to -55 +/- 11 mmHg) and bradycardia (-16 +/- 5 to -116 +/- 40 bpm). Injection of the catalase inhibitor 3-amino-1,2,4-triazole (100 nmol/40 nl) into the NTS also produced hypotension and bradycardia. Previous injection of the ionotropic L-glutamate receptor antagonist kynurenate (7 nmol/40 nl) attenuated by 48% the bradycardic response, without changing the hypotension evoked by H (2) O (2) (500 pmol/40 nl) in anesthetized rats. The antioxidant L-ascorbate (600 pmol/80 nl) injected into the NTS attenuated the bradycardic (42%) and hypotensive (67%) responses to H (2) O (2) (500 pmol/40 nl) into the NTS. In conscious rats, injection of H (2) O (2) (50 nmol/100 nl) into the NTS also evoked intense bradycardia (-207 +/- 8 bpm) and hypotension (-54 +/- 6 mmHg) that were abolished by prior injection of kynurenate (7 nmol/100 nl). The results show that H (2) O (2) into the NTS induces hypotension and bradycardia probably due to activation of glutamatergic mechanisms. |
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