to understand further the action of opioids on growth , s20y neuroblastoma cells in tissue culture were exposed to i ) [ met5 ] -enkephalin , a naturally occurring opioid pentapeptide , at a concentration ( 10 ( -6 ) m ) that inhibits cell replication by 66 % of control levels , ii ) [ met5 ] -enkephalin ( 10 ( -6 ) m ) and the opioid antagonist naloxone ( 10 ( -6 ) m ) which blocks opioid agonist action , or iii ) naltrexone ( 10 ( -6 ) m ) , a potent antagonist that disrupts endogenous opioid-opioid receptor interaction and increased cell number 76 % above control values .
C0027358
naloxone
C0027360
naltrexone