Naturally occurring opioid peptides modulate H+-production by isolated rat parietal cells.
The rationale for the present study was to determine the effects of naturally occurring opioid peptides on H+-production by isolated rat parietal cells as indirectly measured by [14C]-aminopyrine uptake. In crude preparations (18 to 25% parietal cells) and in enriched (80 to 90%) parietal cell fractions stimulation by submaximal histamine- or dibutyryl cAMP-concentrations (10(-6)-10(-4) mol/l) was augmented by 20-30% in the presence of methionine-enkephalin (Met-Enk) and Met-Enk Arg6Phe7 (10(-7) to 10(-5) mol/l). This augmentation was blocked by the opiate receptor antagonist (-)naloxone (10(-6) mol/l) suggesting specificity of the action of Met-Enk and Met-Enk Arg6Phe7. At 10(-6) mol/l (-)naloxone did not exert nonspecific toxic effects. Yet, even in the absence of exogenous opioids, histamine-induced H+-production was inhibited by 3 X 10(-5) or 10(-4) mol/l (-)naloxone. Since similar inhibition occurred with (+)naloxone, an inactive stereoisomer which does not interact with opiate receptors, effects of (-)naloxone at concentrations above 10(-5) mol/l must be considered nonspecific. We conclude that Met-Enk and Met-Enk Arg6Phe7 have no effect on basal, but augment stimulated H+-production by a direct effect on the parietal cells. At nontoxic concentrations (-)naloxone antagonizes this augmentation indicating that it is mediated by specific opiate receptors on the parietal cells.
D000632:Aminopyrine / Q000378:metabolism; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D005260:Female; D005744:Gastric Acid / Q000378:metabolism*; D005753:Gastric Mucosa / Q000166:cytology* / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D000632:Aminopyrine; D009270:Naloxone; D004744:Enkephalin, Methionine; D003994:Bucladesine; C027511:enkephalin-Met, Arg(6)-Phe(7)-; D006632:Histamine