Adrenalin activation of β2-adrenoceptors stimulates morphological changes in astrocytes (pituicytes) cultured from adult rat neurohypophyses

Abstract

Neurohypophysial astrocytes, the pituicytes, are known to undergo morphological changes in vivo in response to stimuli that increase the demand for hormone secretion. Similar changes have been induced by beta-adrenergic stimulation both in the isolated, but otherwise intact, neural lobe and in pituicytes cultured from adult rats. Since the predominant beta-receptor subtype in the neural lobe is beta 2, we investigated the possibility that beta 2-receptor activation is mainly responsible for the observed pituicyte responses. In one experiment, cultured pituicytes were induced by noradrenalin to change from flattened amorphous to stellate morphology. Addition of the beta 2-antagonist IPS 339, but not the beta 1-antagonist practolol, significantly reduced (by 30-60%) the number of cells transformed by noradrenalin. In a second experiment, adrenalin, by definition a more potent beta 2-agonist, transformed significantly more pituicytes into stellate shapes than did noradrenalin at the same concentrations (100% vs. 60% increase, respectively). These results support the idea that beta 2-adrenergic receptors are involved in neurohypophysial plasticity. Also, since the neural lobe is outside of the bloodbrain barrier, these findings suggest that adrenal catecholamines participate in altering pituicyte morphology.