Submitted to: Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 1999
Publication Date: N/A
Interpretive Summary: Adrenomedullin is a newly discovered peptide hormone produced in several tissues in the body and having effects on cardiovascular function, metabolism through effects on insulin and glucose, and growth and differentiation of many tissues and organs. We have discovered that this unique hormone circulates in pplasma bound to a larger protein that we call adrenomedullin binding protein. Other hormones like insulin-like factor--I are also bound to different binding proteins and many of the biological effects of insulin-like growth factor-I are modulated by how these binding proteins assist or retard the hormone in binding to tissues and cells. At this point we have shown that this binding protein is present and conserved across many species from the chicked to humans. We are studying this binding pprotein because of the hope that many of the causes of disease that adrenomedullin is associated with, good and bad effects, could be clinically either better identified or treated with better knowledge of how the biological effects of adrenomedullin are fine tuned by this protein.
More frequently peptide hormones are being demonstrated to circulate in plasma associated with specific binding proteins. Aspects of nonparallel interference with neat serum and plasma in radioimmunoassay procedures for adrenomedullin (AM) prompted a study to determine whether endogenous plasma proteins for AM circulate in association with adrenomedullin. Fundamental 125I-hormone ligand blotting procedures were used to probe for the presence of specific AM binding proteins (AMBPs). Plasma proteins from chicken, cow, dog, goat, human, mouse and pig blood were separated electrophoretically in 10% nonreducing SDS-polyacrylam els, transferred to nitrocellulose, blocked with a BSA/hydrolyzed casein matrix and probed with recombinant human 125I-AM. Phosphoimaging and autoradiogram scanning of blots revealed a 140 kD protein complex in all species tested. Binding of the ligand was specific as judged by a linear competitive displacement of the tracer by increasing molar concentrations of nonlabelled AM in transfer blots of human and bovine plasma. Elution of valid assayable AM from plasma using reverse phase C-18 Sep-Pak7 processing revealed no trace of the high molecular weight AMBP. We conclude that a specific binding protein(s) for AM exist in mammalian blood that might impact on the bioreactivity of AM in health and disease.