LUMINAL PEPTIDE YY-RELEASING FACTORS IN THE ISOLATED VASCULARLY PERFUSED RAT COLON

Peptide YY (PYY) is produced in endocrine L cells primarily localized in the distal bowel. These open-type L cells make contact with the int estinal chyme which may thus affect their secretory activity. The aim of the present study was to examine a large variety of luminal compoun ds found in colonic contents for their potential as PYY-releasing fact ors, using the isolated vascularly perfused rat colon. The release of PW into the portal effluent was measured by a specific RIA. Luminal ad ministration of 5 mM glucose or 0.5% (w/v) starch for 30 min did not i nduce significant release of PYY. Oleic acid (10 and 100 mM) also did not significantly increase PW secretion. A pharmacological concentrati on of glucose (250 mM) and a mixture of amino acids (total concentrati on 250 mM) both induced PW secretion (200% of basal). Pectin, a polyga lacturonic acid, evoked dose-dependent secretion of PYY-like immunorea ctivity over the range 0.1-0.5% (w/v). The maximal response was observ ed after infusion of 0-5% pectin which induced a prompt and sustained release of PW (300% of basal). Galacturonic acid itself (5%) produced marked PW secretion. Gum arabic (0.5%) induced a gradual increase in p ortal PW concentration (maximal response 250% of the basal value) wher eas cellulose (0.5%) did not elicit PW secretion. Luminal n-butyrate o ver the range 0.5-5 mM produced a dose-dependent release of PYY (maxim al response 300% of the basal value with 5 mM n-butyrate). Increasing the concentration of n-butyrate to 100 mM provoked a gradual decrease in PW secretion. Propionate was a less potent stimulant than n-butyrat e, and acetate did not increase PW secretion above the basal value. At a concentration of 2 or 20 mM, taurocholate, cholate and deoxycholate brought about PW secretion while hyodeoxycholate was without effect. In conclusion, glucose and amino acids may mediate PW release but only when they are present at high supraphysiological concentrations in th e colon while oleic acid does not produce any PW secretion. Physiologi cal concentrations of fibers (pectin, gum arabic), shea-chain fatty ac ids (n-butyrate, propionate) and bile salts (taurocholate, cholate, de oxycholate) are all potent stimulants of PW release. Whether the relea se of PW by luminal factors is coupled to water and electrolyte transf er via a local/paracrine pathway remains an open question which requir es additional work with the isolated vascularly perfused colon prepara tion.