Plasma nitrate (A) and nitrite (B) levels in awake lambs after infusion of intravenous HBOC-201 alone (n=3), intravenous HBOC-201 with pretreatment by inhaled nitric oxide (80 ppm, 1 h; n=3), intravenous HBOC-201 with pretreatment by inhaled nitric oxide (80 ppm, 1 h) followed by continuously breathing nitric oxide (5 ppm, 2 h; n=5; high/low iNO), or intravenous HBOC-201 after nitrite infusion (n=4). *p<0.05 HBOC-201 with pretreatment by inhaled nitric oxide and HBOC-201 with high/low inhaled nitric oxide differ from HBOC-201 alone, †p<0.05 HBOC-201 after nitrite bolus differs from HBOC-201 alone, ‡p<0.05 HBOC-201 after nitrite bolus differs from its own baseline.