Tissue-specific dopaminergic regulation of the glucocorticoid receptor in the rat pituitary

The rat intermediate pituitary lobe is one of the rare tissues that is not a known glucocorticoid target and is devoid of immunoreactive glucocorticoid receptor. The intermediate lobe is poorly vascularized and receives a dopaminergic and serotonergic innervation from the hypothalamus. In previous studies we demonstrated that removal of this hypothalamic input results in the appearance of immunoreactive glucocorticoid receptor in the intermediate lobe, as demonstrated with the use of in vitro intermediate pituitary cultures and two in vivo experimental situations. We now show that this appearance of the glucocorticoid receptor is presumably due to removal of hypothalamic dopamine from the intermediate lobe cells, since in this study dopamine (or its potent agonist bromocriptine) inhibits expression of the glucocorticoid receptor in intermediate pituitary cells in primary culture, as demonstrated by [3H] dexamethasone binding and immunocytochemistry. The dopamine antagonist haloperidol blocks the inhibitory effects of the dopamine agonist. In contrast to the intermediate pituitary cells, bromocriptine does not affect glucocorticoid receptor expression in anterior pituitary cells in culture. The differential dopaminergic regulation of glucocorticoid receptor expression in the pituitary gland raises questions about possible effects of dopamine on glucocorticoid receptor levels and glucocorticoid response in other dopamine target tissues, especially in the brain.