| OPRD | opiate receptor delta |
|---|---|
| OPRK | opiate receptor kappa |
| ORA | opiate receptor agonist |
| ER | efficiency ratio; epigastric region; ejection rate; electroresection; emergency room; endoplasmic re... |
| RAR | rapidly adapting receptor; rat insulin receptor; retinoic acid receptor; right arm reclining; right ... |