MODULATION BY OPIOID-PEPTIDES OF MECHANOSENSORY PATHWAYS SUPPLYING THE GUINEA-PIG INFERIOR MESENTERIC GANGLION

1. Radioimmunological techniques were used in isolated guinea-pig infe rior mesenteric ganglion (IMG)-colon preparations to determine whether opioid peptides and neurotensins(8-13) (NT8-(13)), the C-terminal reg ion of NT1-13 recognized by neurotensin receptors, modulate distension -induced release of substance P (SP)- and vasoactive intestinal polype ptide (VIP)-like immunoreactive (LI) material. 2. Colonic distension s ignificantly increased the amount of SP- and VIP-LI material released in the ganglionic superfusate. A low-Ca2+ (0.1 mM), high-Mg2+ (15 mM) solution blocked their release. 3. In vivo capsaicin pretreatment abol ished release of SP-LI material during colonic distension but had no s ignificant effect on distension-induced release of VIP-LI material. 4. The addition of [Leu(5)]enkephalin, [Met(5)]enkephalin, PL017 (a mu-r eceptor agonist) and DPDPE (a delta-receptor agonist) to the ganglion side of a two-compartment chamber blocked distension-induced release o f SP-LI material. The addition of naloxone and ICI-174,864 (a delta-re ceptor antagonist) to the ganglion compartment reversed the inhibitory effect of the mu- and delta-receptor agonists. 5. Addition of [Leu(5) ]enkephalin and [Met(5)]enkephalin to the ganglion compartment had no significant effect on release of VIP-LI material during colonic disten sion. 6. Addition of NT8-13 to the ganglion compartment significantly increased in the amount of XP-LI material released during colonic dist ension but had no affect on distension-induced release of VIP-LI mater ial. 7. The results suggest the hypothesis that under in vivo conditio ns, enkephalinergic nerves decrease and neurotensinergic nerves increa se the release of SP from peripheral branches of primary afferent sens ory nerves.