Effects of hydralazine on adrenal and cardiac sympathetic nerve activity in anesthetized rats

The present study was carried out to elucidate whether there is a correlation between hydralazine-induced tachycardia and the increase in cardiac sympathetic nerve activity in buffer nerve-intact and debuffered rats. Hydralazine (1 mg/kg, i.v.) produced a significant decrease in mean arterial blood pressure immediately after injection in both buffer nerve-intact rats and debuffered rats. A few min after hydralazine administration, increases in cardiac sympathetic nerve activity and heart rate were observed in both rat groups. Moreover, after hydralazine injection, adrenal sympathetic nerve activity increased in the debuffered rat group. These results suggest that hydralazine-induced tachycardia is not only reflexly induced, but that it is also mediated via direct excitation of the central nervous system in rats.