Intermedin/Adrenomedullin-2 Inhibits Growth Hormone Release from Cultured, Primary Anterior Pituitary Cells

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Abstract
Intermedin (IMD), a novel member of the adrenomedullin (AM), calcitonin gene-related peptide (CGRP), amylin (AMY) peptide family, has been reported to act promiscuously at all the known receptors for these peptides. Like AM and CGRP, IMD acts in the circulation to decrease blood pressure and in the brain to inhibit food intake, effects that could be explained by activation of the known CGRP, AM, or AMY receptors. Because AM, CGRP, and AMY have been reported to affect hormone secretion from the anterior pituitary gland, we examined the effects of IMD on GH, ACTH, and prolactin secretion from dispersed anterior pituitary cells harvested from adult male rats. IMD, in log molar concentrations ranging from 1.0 pm to 100 nm, failed to significantly alter basal release of the three hormones. Similarly, IMD failed to significantly alter CRH-stimulated ACTH or TRH-stimulated prolactin secretion in vitro. However, IMD concentration-dependently inhibited GHRH-stimulated GH release from these cell cultures. The effects of IMD, although requiring higher concentrations, were as efficacious as those of somatostatin and, like somatostatin, may be mediated, at least in part, by decreasing cAMP accumulation. These actions of IMD were not shared by other members of the AM-CGRP-AMY family of peptides, suggesting the presence of a novel, unique IMD receptor in the anterior pituitary gland and a potential neuroendocrine action of IMD to interact with the hypothalamic mechanisms controlling growth and metabolism.