Regional distribution of noradrenaline and dopamine-beta-hydroxylase in the brain of spontaneously hypertensive rats

Abstract

The catecholamine concentration and dopamine-beta-hydroxylase activity were determined in several nuclei of the brain of spontaneously hypertensive rats (SHR) compared with Wistar Kyoto (WKY) controls. Catecholamines were measured by using liquid chromatography coupled with electrochemical detection. The threshold of detection was 5 X 10(-14) mole. Dopamine-beta-hydroxylase (DBH) was assayed by a sensitive radioenzymatic assay using tyramine as the substrate. The limit of detection was 5 pmoles of octopamine per sample. Significantly lower noradrenaline content was observed in 4 week-old SHR in some medullary and hypothalamic areas which are involved in cardiovascular regulation. This abnormally was no longer detectable in 12 week-old rats. The changes in catecholamine levels observed in young rats were not observed during the development of deoxycorticosterone-salt hypertension and therefore probably do not represent a compensatory mechanism tending to limit the progressive rise blood pressure. No significant difference in DBH activity was observed between the young SHR and WKY in any brain region measured. The altered relationship between noradrenaline content and DBH activity observed in young SHR when compared to WKY suggests a change in noradrenergic neurones activity and/or structure which could correspond to a genetically transmitted neurochemical abnormality associated with the initiation of hypertension in the SHR.