Functional consequences of neuropeptide Y Y 2 receptor knockout and Y 2 antagonism in mouse and human colonic tissues

Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) differentially activate three Y receptors (Y 1 , Y 2 and Y 4 ) in mouse and human isolated colon. The aim of this study was to characterise Y 2 receptor‐mediated responses in colon mucosa and longitudinal smooth muscle preparations from wild type (Y 2 +/+) and knockout (Y 2 −/−) mice and to compare the former with human mucosal Y agonist responses. Inhibition of mucosal short‐circuit current and increases in muscle tone were monitored in colonic tissues from Y 2 +/+ and Y 2 −/− mice±Y 1 (( R )‐ N ‐[[4‐(aminocarbonylaminomethyl)phenyl)methyl]‐ N 2 ‐(diphenylacetyl)‐argininamide‐trifluoroacetate (BIBO3304) or Y 2 ( S )‐ N 2 ‐[[1‐[2‐[4‐[( R , S )‐5,11‐dihydro‐6(6H)‐oxodibenz[b,e]azepin‐11‐yl]‐1‐piperazinyl]‐2‐oxoethyl]cyclopentyl]acetyl]‐ N ‐[2‐[1,2‐dihydro‐3,5(4H)‐dioxo‐1,2‐diphenyl‐3H‐1,2,4‐triazol‐4‐yl]ethyl]‐argininamide (BIIE0246) antagonists. Predictably, Y 2 −/− tissues were insensitive to Y 2 ‐preferred agonist PYY(3‐36) (100 n M ), but unexpectedly Y 4 ‐preferred PP responses were right‐shifted probably as a consequence of elevated circulating PP levels, particularly in male Y 2 −/− mice (Sainsbury et al ., 2002). BIBO3304 and BIIE0246 elevated mucosal ion transport, indicating blockade of inhibitory mucosal tone in Y 2 +/+ tissue. While BIBO3304 effects were unchanged, those to BIIE0246 were absent in Y 2 −/− mucosae. Neither antagonist altered muscle tone; however, BIIE0246 blocked NPY and PYY(3‐36) increases in Y 2 +/+ basal tone. BIBO3304 abolished residual Y 1 ‐mediated NPY responses in Y 2 −/− smooth muscle. Tetrodotoxin significantly reduced BIIE0246 and PYY(3‐36) effects in Y 2 +/+ mouse and human mucosae, but had no effect upon Y‐agonist contractile responses, indicating that Y 2 receptors are located on submucosal, but not myenteric neurones. Tonic activation of submucosal Y 2 receptors by endogenous NPY, PYY or PYY(3‐36) could indirectly reduce mucosal ion transport in murine and human colon, while direct activation of Y 2 receptors on longitudinal muscle results in contraction.British Journal of Pharmacology (2003) 139 , 863–871. doi: 10.1038/sj.bjp.0705298