DISTRIBUTION OF OPIATE-LIKE SUBSTANCES IN RAT-TISSUES

Rat tissues were tested for their ability to inhibit the binding of [3H]dihydromorphine or [3H]naloxone to membrane-bound opiate receptors. By this criterion, morphine-like substances were found in lung, heart, liver, and kidney as well as in brain. The relative activity of the extracts, based on initial tissue weight, differed with the radioactive ligand employed. With dihydromorphine, the order was as above. With naloxone, lung was most active, followed by heart, brain, liver, and kidney. The ability of all tissue extracts to inhibit opiate binding was reduced by 100 mM NaCl and slightly reduced by 1 mM MnCl2. Gel filtration using Sephadex G-25 indicated that the inhibitory Substances were heterogeneous in molecular weight. Only with brain and kidney extracts was there significant activity at the elution volume where enkephalins would be expected. Fraction tion using Amberlite XAD-2, a resin which selectively absorbs hydrophobic materials, again indicated that the major portion of activit in all tissue extracts was due to substances other than enkephalins. © 1979 Plenum Publishing Corporation.