Regional changes in brain noradrenergic activity elicited by a decrease in blood pressure.

Using high performance liquid chromatography with electrochemical detection, the level of 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), an index of noradrenaline release, was determined in regions of the brainstem and hypothalamus of rats after acute hypotension induced by hydralazine. In hypotensive rats, an increase in MHPG concentrations was observed in the posterior hypothalamus, while no significant changes were seen for all the other regions. These results suggest that hypotension results in an enhancement of noradrenaline release in the posterior hypothalamus in rats.