Respiratory effects of 5'-ethylcarboxamidoadenosine, an analog of adenosine, following microinjections into the nucleus tractus solitarius of rats.

Microinjections of 5'-ethylcarboxamidoadenosine (NECA), an adenosine analog, were made into respiratory-related regions of the nucleus tractus solitarius (NTS) of spontaneously breathing rats and cardiorespiratory parameters were recorded during a 60-min test period. Microinjections of NECA, in the dose range of 0.35-350 picomol per rat, produced significant dose-related reductions in respiratory rate which were accompanied by correlative increases in tidal volume. At the end of the 60-min test period following the administration of NECA, the respiratory rate remained profoundly depressed, whereas blood pressure and heart rate were not significantly affected compared to preinjection control values. The data from this study suggest that adenosine may exert modulatory influences in brainstem respiratory control regions.