This study will investigate basic mechanisms underlying cellular and subcellular responses of pituitary cells to corticotropin releasing hormone (CRH) and specific modulators of CRH action. It is focused on anterior lobe corticotropes and will study CRH binding and internalization (with quantitative electron microscopic cytochemical analyses) and hormone storage (with immunocytochemistry). The study will determine if inhibitors (glucocorticoids) or potentiators (vasopressin) of ACTH release alter the rate or route of CRH processing by corticotropes. The reserve cell population that is activated to bind CRH in the presence of the potentiator, vasopressin, will be identified. The study will test the hypothesis that potentiation of CRH action is dependent upon the activation of unique vasopressin sensitive cells that have the potential to produce ACTH. Another hypothesis that will be tested is that glucocorticoid inhibition of CRH action, in its early stages, includes either a block in the transport of CRH receptors to the plasma membrane or a rerouting of CRH-receptor complexes to lysosomes for rapid degradation. Changes in CRH binding will be identified with a biotinylated CRH ligand and labelled avidin stains. All cytochemical stains will be analyzed with the Bioquant System IV and image analysis system. The results of this research will enhance the understanding of basic mechanisms regulating the release of hormone by one type of pituitary cell, the corticotrope.
