CART (Cocaine- and Amphetamine-Regulated Transcript) peptides modulate food intake and psychostimulant drug actions. Several CART peptides that contain multiple disulfide bonds were produced by overexpression in Escherichia coli bacteria as fusion products with a C-terminal histidine tag. Since these peptides were found denatured in inclusion bodies, in vitro refolding was used to reconstitute their biological activity. These CART peptides were tested for their ability to inhibit food intake in rats. Of recombinant rat CART peptides 1-102 long, 1-102 short, and 55-102, only CART peptide 55-102 dose-dependently inhibited neuropeptide Y stimulated food intake in rats. This effect was dependent on refolding of the peptide since the unfolded version was unable to inhibit food intake. Unfolded CART peptide 55-102 HIS tag, but not CART peptide 1-102 HIS tag, stimulated food intake in rats treated with NPY or vehicle. This effect of unfolded CART peptide 55-102 was consistent with that of an antagonist and is the first description of one. These studies showed that production of CART peptides by bacterial expression is a viable alternative to current methods. (C) 2003 Elsevier Inc. All rights reserved.