Dopamine inhibits the release of immunoreactive beta-endorphin from rat hypothalamus in vitro.
Mediobasal hypothalamus tissue (MBH) from adult male rats was incubated in Krebs-Ringer bicarbonate medium (KRB). KRB was changed at 15 min intervals and the concentration of immunoreactive beta-endorphin (beta-ENDi) in the medium was measured by radioimmunoassay. Incubation of MBH tissue in normal KRB resulted in a constant release rate of beta-ENDi of approximately 1% of the tissue content per h. KRB containing 45 mM K+ causes a two fold increase in the release rate of beta-ENDi which was Ca2+ dependent. Dopamine (0.01-1.0 microM) inhibits both the spontaneous and the K+-stimulated release of beta-ENDi in a dose related manner. The dopamine receptor blocking agent haloperidol prevents this inhibitory effect of dopamine. The selective D-1 receptor agonist SKF 38393 does not affect the release rate of beta-ENDi; whereas the selective D-2 receptor agonist LY 141865 inhibits both the spontaneous and K+-stimulated release of beta-ENDi. The effects of LY 141865 can be blocked by (-)-sulpiride, a selective D-2 receptor antagonist. Norepinephrine only weakly inhibits the K+-stimulated release of beta-ENDi, an effect that can be blocked by haloperidol but not by the alpha-adrenoceptor blocker phentolamine. At concentrations tested (0.01-1.0 microM), isoproterenol, 5-hydroxytryptamine, carbachol and 8-Br-cAMP (1.0 microM) do not affect beta-ENDi release. It is concluded that dopamine can inhibit the release of beta-ENDi from hypothalamic neurons via a D-2 receptor mechanism.
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D000818:Animals; D004298:Dopamine / Q000494:pharmacology* / Q000502:physiology; D004723:Endorphins / Q000378:metabolism*; D006220:Haloperidol / Q000494:pharmacology; D007033:Hypothalamus, Middle / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000502:physiology; D017448:Receptors, Dopamine D2; D001615:beta-Endorphin
D004723:Endorphins; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D001615:beta-Endorphin; D006220:Haloperidol; D004298:Dopamine; D009638:Norepinephrine