Table 2

Concentration of DOPAC and ratio DOPAC/DA in left atria 30 min after naloxone (1 mg/kg s.c.) or saline administration in rats chronically treated with placebo or morphine pellets

TreatmentDOPAC (ng/g)DOPAC/DA
Placebo + saline27.0  ± 5.80.68  ± 0.08
Placebo + naloxone15.4  ± 0.80.67  ± 0.1
Morphine + saline19.0  ± 2.00.80  ± 0.05
Morphine + naloxone8.80  ± 0.82-a,2-b 1.18  ± 0.22-c

  • Mean ± S.E.M. of 5 to 6 experiments for each experimental group.

  • ↵2-a P < .01 vs. morphine + saline.

  • ↵2-b P < .001 vs. placebo + naloxone.

  • ↵2-c P < .05 vs. morphine + saline.