Fig. 5. (A ) Cumulative concentration–response curves to murine tetrameric hemoglobin and PolyHeme (Northfield Laboratories, Evanston, IL) (6 × 10−9to 1.8 × 10−5m) in aortic rings obtained from wild-type (WT) and db/db mice, n = 6–8. *P < 0.05 tetrameric hemoglobin-WT differs from tetrameric hemoglobin (Hb)-db/db. †P < 0.05 tetrameric hemoglobin-db/db differs from PolyHeme-db/db. ‡P < 0.05 tetrameric hemoglobin-WT differs from PolyHeme-WT. §P < 0.05 PolyHeme-db/db differs from PolyHeme WT. (B ) Cumulative concentration–response curves to murine tetrameric hemoglobin and PolyHeme (6 × 10−9to 1.8 × 10−5m) treated with or without l-NAME (10−7m) in aortic rings obtained from WT mice, n = 6–8. **P < 0.05 l-NAME + tetrameric hemoglobin differs versus tetrameric hemoglobin without l-NAME. §§P < 0.05 l-NAME + PolyHeme differs from PolyHeme alone. l-NAME =N G-nitro-l-arginine methyl ester.