Abstract
The antidiarrheal and constipating effects of opiates are partly attributed to reductions in active anion secretion across the intestinal mucosa that are modulated by submucosal neurons. In this study, the opioid receptor mediating the actions of opioids on ion transport was characterized in mucosa-submucosa sheets from porcine ileum. Electrical transmural stimulation evoked transient increases in short-circuit current, an electrical measure of neurogenic ion transport, in this preparation. After serosal addition, the peptidic δ-opioid agonists [d-Ala2]-deltorphin II (pIC50 = 8.4 ± 0.7), [d-Ala2,d-Leu5]-enkephalin (DADLE), [d-Pen2,d-Pen5]-enkephalin (DPDPE), and [d-Ser2,Leu5,Thr6]-enkephalin (DSLET), and the μ-opioid agonists [d-Ala2,N-methyl-Phe4,Gly5-ol]-enkephalin (DAMGO) (pIC50 = 8.0 ± 0.1), endomorphin I, and PL-017 inhibited short-circuit current elevations. Nonpeptidic μ- or δ-opioid agonists (morphine, loperamide, and SNC80) and κ-opioid agonists (U-50,488H and U-69,593) were <360-fold less potent than deltorphin II. At 100 nM, the δ1-opioid antagonist 7-benzylidenenaltrexone reduced the potencies of DPDPE and DAMGO by 13.5- and 15.5-fold, respectively; at an identical concentration naltriben, a δ2-opioid antagonist, or the μ-opioid antagonistd-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr-NH2(CTOP) reduced DPDPE potency by 4.1- and 3.4-fold, respectively, but had no significant effect on DAMGO potency. Using primary antisera directed toward cloned opioid receptors, δ-opioid receptor immunoreactivity was immunohistochemically localized in submucosal neurons and nerve fibers, but immunoreactivities to κ- or μ-opioid receptors were not detected in the mucosa-submucosa. These results suggest that a novel 7-benzylidenenaltrexone-sensitive opioid receptor is expressed in submucosal neurons of the porcine ileum, which mediates the inhibitory effects of peptidic μ- and δ-opioid agonists on neurogenic ion transport.
Footnotes
-
Send reprint requests to: David R. Brown, Ph.D., Department of Veterinary PathoBiology, University of Minnesota, 1988 Fitch Ave., St. Paul, MN 55108-6010. E-mail:brown013{at}tc.umn.edu
-
This investigation was supported by National Institutes of Health Grant R01 DA-10200 to D.R.B. and R01 DA-01533 to P.S.P. S.P. was supported by a Royal Thai Government scholarship.
- Abbreviations:
- OR
- opioid receptor
- DADLE
- [d-Ala2,d-Leu5]-enkephalin
- DPDPE
- [d-Pen2,d-Pen5]-enkephalin
- DSLET
- [d-Ser2,Leu5,Thr6]-enkephalin
- DAMGO
- [d-Ala2,N-methyl-Phe4,Gly5-ol]-enkephalin
- PL-017
- [methyl-Phe3,d-Pro4]morphiceptin
- TIPP
- Tyr-1,2,3,4-tetrahydroisoquinoline-Phe-Phe-OH
- CTOP
- d-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr-NH2
- SNC80
- (+)-4-[(αR)-α(2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl-3-methoxybenzyl)-N,N-diethylbenzamide
- U-50,488H
- trans-(±)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl]cyclohexyl) benzene-acetamide methanesulfonate
- U-69,593
- (5α,7α,8β)-(+)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl)]-benzeneacetamide
- NTB
- naltriben
- BNTX
- 7-benzylidenenaltrexone
- BSINTX
- 7-(5′,6′-benzo-2′-spiro-indanyl)naltrexone
- Isc
- short-circuit current
- Gt
- tissue electrical conductance
- ETS
- electrical transmural stimulation
- PBS
- phosphate-buffered saline
- Received September 19, 2000.
- Accepted January 17, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|