Involvement of oxytocin in the nucleus tractus solitarii on central cardiovascular control: interactions with glutamate.

Oxytocin (OT) is a peptide involved in several physiological functions in the central nervous system including central cardiovascular regulation. To clarify the role of endogenous OT in cardiovascular control, one group of anesthetized rats received unilateral microinjections of the OT receptor antagonist [d(CH(2))(5),Tyr(Me)(2),Orn(8)]-vasotocin (OTA) in the nucleus tractus solitarii (NTS) and a second group was injected with specific OT antiserum (Anti-OT). Moreover, the modulation of the cardiovascular effect of L-glutamate (GLU) by OT was also evaluated by cardiovascular analysis using effective and threshold doses of GLU. Mean arterial pressure (MAP) and heart rate (HR) were measured from a femoral catheter. OTA significantly (p<0.01) decreased the vasopressor and tachycardiac long-lasting response elicited by an effective dose of OT. Microinjections of Anti-OT antibody did not modify the values of MAP and HR compared with the control group. With regard to the OT/GLU coinjections, a subthreshold dose of OT significantly (p<0.001) counteracted the vasodepressor and bradycardiac responses induced by GLU. The coinjection of subthreshold doses of OT and GLU did not produce a change in MAP or in HR. These findings seem to exclude an endogenous tonic action of OT on central regulation of MAP and HR, although they confirm the significant role of OT on central cardiovascular control within the NTS. In fact, the modulation of GLU responses by OT supports the importance of OT on the central cardiovascular adjustments likely acting on the baroreceptor reflex sensitivity.