Resistin (resistanceto insulin), also known as adipocytespecific secretory factor (ADSF) and found in inflammatory zone 3 (FIZZ3), is a 10kD member of a small family of secreted cysteinerich peptide hormones. These molecules purportedly play some role in inflammation, glucose metabolism, and angiogenesis (1, 2, 3, 4). Human Resistin precursor is 108 amino acids (aa) in length. It contains an 18 aa signal sequence plus a 90 aa mature region. The mature region shows an Nterminal ahelical tail (aa 23 44) and a Cterminal Bsheet globular head (aa 47 108) (5 7). The Resistin molecule circulates as either a noncovalent trimer (minor form), or a disulfidelinked homohexamer (major form). Noncovalent trimers are generated when the ahelical segments selfassociate to form a threestranded coiledcoil structure. Covalent hexamers subsequently appear when the free Cys at position #26 is engaged by adjacent trimers. It is hypothesized that the hexamer is the inactive form of the molecule, and bioactivity is achieved at the target site by disulfide bond reduction (5). Although Resistin family molecules can noncovalently interact to form heterotrimers in vitro, there is no evidence to suggest this occurs in vivo with Resistin (8, 9). Mature human Resistin shares 56% and 54% aa identity with mouse and rat Resistin, respectively. Rat Resistin possesses an alternate start site at Met48; this Met is not found in the mouse molecule, however (10). Rodent Resistin is expressed by white adipocytes, splenocytes, astrocytes, and anterior pituitary epithelium (6, 11, 12). Although the function of Resistin is unclear, it would seem to block insulinstimulated uptake of glucose by adipocytes and promote glucose release by hepatocytes (6, 13, 14). As such, it has been proposed to participate in dietinduced insulinsensitivity. Diets high in fat promote an increase in overall adipocyte size. Hypertrophic adipocytes are known to secrete TNFa which acts locally to block ACRP30 production. Since ACRP30 is an insulinsensitizer, a drop in ACRP30 availability leads to insulininsensitivity, which drives increased insulin production (a compensatory mechanism). High insulin induces Resistin secretion which now antagonizes insulin action, prompting more insulin production and more Resistin secretion (15).