Electrogenic Cl– and K+ secretion in isolated mucosa from guinea pig distal colon measured as short-circuit current (Isc) and transepithelial conductance (Gt) were stimulated by epinephrine (epi), prostaglandin-E2 (PGE2) and carbachol (CCh). neuropeptide-Y (NPY) and peptide-YY (PYY) inhibited by 60% Cl– secretion activated by either PGE2 or PGE2+CCh with EC50’s of 16nM and 6nM, respectively. Neither peptide markedly inhibited the transient component of the PGE2+CCh response. Immunoreactivity (IR) for NPY was present in enteric ganglia and in proximity with crypts. Basolateral membranes of colonic crypt and surface epithelial cells had distinct IR for neuropeptide-Y receptors Y1 and Y2. Receptor expression was supported further by immuno-blot showing bands at molecular weights consistent with monomer and oligomer. Sub-type selective antagonists BVD10 (Y1) and BIIE0246 (Y2) indicated that secretory suppression occurred through Y2 receptors. The Y2 selective peptide PYY(3-36) also suppressed Cl– secretion with a EC50 of 9nM. BIIE0246 addition increased Isc and Gt during PGE2 or PGE2+CCh activation consistent with the presence of in vitro released PYY or NPY. PYY addition increased the epi EC50 to 18nM compared with BIIE0246 treated tissues, 4nM. Thus, PYY or NPY suppressed Cl– secretory capacity and desensitized the adrenergic K+ secretory response, providing a negative feedback for secretory activation. [supported by NIH, DK65845]