Adrenergic regulation of hypothalamic proenkephalin neurons: evidence for opposite effects in subpopulations terminating in median eminence and neurointermediate pituitary.

The effect of adrenergic influences on Met-enkephalin concentrations in median eminence, neurointermediate pituitary and hypothalamus outside median eminence were examined. Met-enkephalin levels in median eminence were augmented by administration of the alpha 1-adrenergic agonist methoxamine acutely or chronically and decreased by the selective depletion of adrenergic transmitters by 6-hydroxydopamine. Met-enkephalin levels in neurointermediate lobe were decreased by methoxamine but unaffected by depletion of noradrenaline/adrenaline. These results indicate that adrenergic mechanisms maintain Met-enkephalin concentrations tonically in median eminence and deplete Met-enkephalin concentrations in neurointermediate lobe. These results suggest differential adrenergic regulation of hypothalamic proenkephalin neurons terminating in median eminence and neural lobe of pituitary.