Binding capacities and affinities at mu-, delta- and kappa-opioid sites in membrane suspensions from guinea-pig brain regions.
Binding capacities and affinities (KD) of ligands at mu-, delta- and kappa-opioid binding sites were determined by selective labelling techniques together with analysis of saturation curves in seven regions of the guinea-pig brain. The kappa-sites predominated over the other sites in most regions and were 90% of the total in the cerebellum; binding capacities at kappa-sites were highest in the cortex, intermediate in the cerebellum, striatum and mesencephalon and lowest in the diencephalon, hippocampus and pons-medulla. At the mu-sites, binding capacities were highest in the diencephalon and mesencephalon, with intermediate levels in the pons-medulla, cortex and striatum, and low levels in the hippocampus and cerebellum. The highest binding capacity at the delta-sites was in the striatum, intermediate in the cortex, diencephalon and hippocampus, low in the mesencephalon and pons-medulla and not detectable in the cerebellum. No regional differences in binding affinities were found at mu-, delta- and kappa-sites with [3H]-[D-Ala2,MePhe4,Gly-ol5]enkephalin (KD = 1.10-2,61 nM), [3H]-[D-Ala2,D-Leu5]enkephalin (KD = 0.81-1.94 nM) and [3H]-(-)-bremazocine (KD = 0.083-0.185 nM). Thus in guinea-pig brain there are regional differences in opioid binding capacity and in the distribution of mu-, delta- and kappa-sites, but not in binding affinities.
La Regina
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Istituto di Ricerche Farmacologiche Mario Negri, Milano, Italy.
Colombo
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M
Petrillo
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P
Tavani
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A
D000818:Animals; D001575:Benzomorphans / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016308:Enkephalin, Leucine-2-Alanine / Q000378:metabolism; D004745:Enkephalins / Q000378:metabolism; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D011957:Receptors, Opioid / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu
D001575:Benzomorphans; D004745:Enkephalins; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016308:Enkephalin, Leucine-2-Alanine; C027248:bremazocine