Adrenergic activation of electrogenic K⁺ secretion in isolated mucosa from guinea pig distal colon was desensitized by peptide-YY (PYY). Addition of PYY or neuropeptide-Y (NPY) to the bathing solution of mucosae in Ussing chambers suppressed the short-circuit current (Isc) corresponding to electrogenic Cl^- secretion, whether stimulated by epinephrine (epi), prostaglandin-E₂ (PGE₂), or carbachol (CCh). Neither peptide markedly inhibited the large transient component of synergistic secretion (PGE₂+CCh). Sustained Cl^- secretory I_sc was inhibited ~65% by PYY or NPY, with IC₅₀'s of 4.1±0.9nM and 9.4±3.8nM, respectively. This inhibition was eliminated by BIIE0246, an antagonist of the Y2-neuropeptide receptor (Y2-NpR), but not by Y1-NpR antagonist BVD10. Adrenergic sensitivity for activation of K⁺ secretion in the presence of Y2-NpR blockade by BIIE0246 was (EC₅₀'s) 2.9±1.2nM for epi and 13.3±1.0nM for norepinephrine (norepi), ~4-fold greater than in the presence of PYY. Expression of mRNA for both Y1-NpR and Y2-NpR was indicated by RT-PCR of RNA from colonic mucosa; and, protein expression was indicated by immuno-blot. Immuno-reactivity (ir) for Y1-NpR and Y2-NpR was distinct in basolateral membranes of columnar epithelial cells in the crypts of Lieberkühn as well as inter-crypt surface epithelium. Adrenergic nerves in proximity with crypts were detected by ir for dopamine--hydroxylase (DH), and a portion of these nerves also contained NPY^ir. BIIE0246 addition increased secretagogue-activated I_sc consistent with in vitro release of either PYY or NPY. Thus, PYY and NPY were able to suppress Cl^- secretory capacity and desensitize the adrenergic K⁺ secretory response, providing a direct inhibitory counter-balance against secretory activation.