Role of the rostroventrolateral medulla in moxonidine-induced changes in cardiochronotropic regulation.

The cardiac component of baroreflex and sympathetic tone of the heart were studied in SHR-SP rats receiving moxonidine intragastrically or into the rostroventrolateral medulla. Moxonidine administered intragastrically in a dose of 10 mg/kg had no effect on cardiac sympathetic tone, but reduced the intracardiac rhythm and enhanced baroreflex bradycardia. Local injection of moxonidine into the rostroventrolateral medulla decreased cardiac sympathetic tone, but did not change the amplitude of baroreflex chronotropic responses. Our results indicate that changes in cardiochronotropic regulation after systemic administration of moxonidine are not mediated by the rostroventrolateral zone of the medulla oblongata.