DELTA-OPIOID RECEPTOR MESSENGER-RNA EXPRESSION AND IMMUNOHISTOCHEMICAL LOCALIZATION IN PORCINE ILEUM

Opiates have potent antidiarrheal actions that are mediated in part by delta-opioid receptors (DOR). We examined DOR localization within sub regions of porcine ileum, a tissue analogous to human small bowel. A p artial cDNA sequence for porcine DOR was obtained after reverse transc ription-polymerase chain reaction cloning of forebrain RNA; it encoded the end of transmembrane domain 1 through the beginning of transmembr ane domain 7 and exhibited 93% nucleotide identity with human DOR. Pos itive signals for DOR mRNA were found in all subregions of the porcine ileal wall. With an antiserum recognizing an N-terminal epitope in mu rine DOR, DOR-like immunoreactivity was localized in neurons within my enteric and submucous ganglia, longitudinal and circular smooth muscle , and villous lamina propria. The DOR agonist [D-Ser(2), Leu(5), Thr(6 )]enkephalin (DSLET) attenuated circular smooth muscle contractions in porcine ileum that were evoked by electrical stimulation of myenteric cholinergic neurons. These results are consistent with previous repor ts of the DOR-mediated neuromodulation that underlies the antipropulsi ve and antisecretory effects of opioids in the intestinal tract.