ESR SPECTRAL TRANSITION BY ARTERIOVENOUS CYCLE IN NITRIC-OXIDE HEMOGLOBIN OF CYTOKINE-TREATED RATS

Nitric oxide (NO) generation was induced in rats by Escherichia coli l ipopolysaccharide (LPS) as detected by electron spin resonance (ESR) s ignals of NO hemoglobin (HbNO). However, there were inconsistencies in ESR spectral. shape among them. We have therefore carried out a syste matic study to clarify the in vivo spectral changes. First, the spectr a of the alpha-NO heme species had the distinct three-line hyperfine s tructure in venous blood but not in arterial blood in all rats treated with tumor necrosis factor, interleukin-1, and/or LPS, and methemoglo bin was not detected at the g = 6 (high-spin methemoglobin) region. Se cond, when the treated rats died, the three-line hyperfine structure w as very distinct even in arterial blood. Third, even if HbNO was forme d by injection of nitrite to rats, the three-line hyperfine structure of HbNO in venous blood was more marked than that in arterial blood, i ndependent of the appearance of the methemoglobin signal. Fourth, an e x vivo study using whole blood demonstrated that the three-line hyperf ine structure intensified lineally when O-2 saturation of hemoglobin d ecreased but disappeared on reoxygenation of hemoglobin. These results directly demonstrate in vivo quaternary structural transition of the hemoglobin tetramer from the high-affinity state in the arterial cycle to the low-affinity state in the venous cycle. The transition makes t he diverse ESR spectra of HbNO in vivo.