Control of guinea pig intestinal electrolyte secretion by a delta-opiate receptor.
The effects of opioids on transepithelial potential difference and short-circuit current across guinea pig ileum stripped of one muscle layer were measured in vitro in Ussing chambers. Opioid peptides such as [DAla2, DLeu5]enkephalin and [DAla2, DMet5]enkephalin, which are primarily agonists at delta-opiate receptors, were able to reduce transepithelial potential difference and short-circuit current at concentrations as low as 1 nM. The narcotic drug etorphine was also very potent in reducing short-circuit current, but fentanyl and morphine, which are primarily agonists at mu-opiate receptors, were almost completely ineffective. Ketocyclazocine was relatively ineffective, and beta-endorphin had intermediate potency. All opioid effects could be reversed by the opiate antagonist naloxone. Somatostatin also reduced short-circuit current, but its effect was not reduced by naloxone. Chloride flux measurements indicated that the effect of etorphine on short-circuit current is associated with an enhancement of active Cl- absorption. The relative effects of opioids in this system suggest that their actions are being mediated by a specific delta-opiate receptor. In contrast, opioid effects on guinea pig intestinal smooth muscle seem to be primarily mediated by a mu-opiate receptor.
D000818:Animals; D002712:Chlorides / Q000378:metabolism*; D004553:Electric Conductivity; D004723:Endorphins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005048:Etorphine / Q000494:pharmacology; D005260:Female; D005283:Fentanyl / Q000494:pharmacology; D006168:Guinea Pigs; D007413:Intestinal Mucosa / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects*; D009020:Morphine / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D011957:Receptors, Opioid / Q000502:physiology*
D002712:Chlorides; D004723:Endorphins; D011957:Receptors, Opioid; D009270:Naloxone; D005048:Etorphine; D009020:Morphine; D005283:Fentanyl