c57/bl mice , which have a lowered sensitivity to morphine but a normal response to peptides with low g.p.i./m.v.d . and nal/leu ratios , had a lowered sensitivity to analogues with high ratios.7 in the alkaloid-like series of narcotic analgesic drugs , ketobemidone , levorphanol , methadone , etorphine and the antagonist mr 2266 had lower nal/leu ratios ( 1.0 to 2.8 ) than morphine , normorphine , naloxone and naltrexone ( 8 to 12 ) .8 it would appear that compounds with low g.p.i./m.v.d . and nal/leu ratios interact mainly with delta-receptors in the brain and peripheral nervous system while compounds with high ratios interact mainly with mu-receptors .
C0870814
series
C0006104
brain