Blood vessel specific vaso-activity to nitrite under normoxic and hypoxic conditions

This study uses an organ chamber bioactivity assay to characterise the direct effect of sodium nitrite upon rabbit blood vessels (aorta (Ao), inferior vena cava (IVC) and pulmonary artery (PA)) in a haemoglobin independent/variable oxygen environment. In 95% oxygen constriction to 8g (Ao), 6g (PA) and 4g (IVC) was achieved using 1μM phenylephrine. The same constriction in 1% oxygen required 3μM. During 95% oxygen constriction was consistent and sustained for all vessels. However under 1% oxygen PA was quick to constrict but rapidly gave up this tension whereas Ao was slower to constrict but exhibited a more sustained response. Relaxation of each vessel was assessed post constriction using 10μM sodium nitrite. Results were expressed as a percentage loss in tension compared to the maximum achieved and corrected by controls which received no nitrite. At 95% oxygen PA relaxed greater than Ao (10.04% ± 2.28% vs. 5.25% ± 1.51%). IVC response was varied (2.26% ± 9.43%). At 1% oxygen all vessels relaxed more. However the pattern was reversed with both IVC (14.20% ± 3.63%) and PA (16.55% ± 0.93%) relaxing less than Ao (42.20% ± 5.21%). These results suggest that relatively low concentrations of sodium nitrite can vasodilate blood vessels. This effect is independent of haemoglobin and tissue specific.