DENERVATION HYPERSENSITIVITY TO CENTRALLY ADMINISTERED NORADRENALINE RESULTING FROM INTRAVENTRICULAR ADMINISTRATION OF 6-HYDROXYDOPAMINE WITH SPECIAL REFERENCE TO THE PITUITARY-ADRENOCORTICAL RESPONSE AND ITS DEPENDENCE ON THE BASAL LEVEL OF CORTICOSTERONE IN THE RAT

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Abstract
The dexamethasone-induced suppression of the level of corticosterone in the plasma was slightly, but significantly counteracted by intraventricular administration of noradrenaline [norepinephrine] and the response was more marked in rats pretreated with 6-hydroxydopamine. This result also indicates the development of denervation hypersensitivity and it is noteworthy that the suppression experiments were performed at 15.00 h. These results, together with those from the 08.00 h experiments, suggest that the basal level of corticosterone is more important than the diurnal variability in responsiveness, i.e., lower basal concentrations of hormone are associated with more pronounced responses. It appears that intraventricular administration of 6-hydroxydopamine may cause the development of denervation hypersensitivity and that the responsiveness of the pituitary-adrenococrtical system to the subsequent intraventricular administration of noradrenaline is dependent on the basal level of corticosterone in the plasma at the time of the noradrenaline injection.

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