High blood levels of nitric oxide in rats subjected to prolonged respiratory arrest and their modulation during adrenocorticotropin-induced resuscitation

Abstract

Anaesthetized rats, endotracheally intubated and mechanically ventilated with room air, were subjected to a 5-min period of asphyxia by turning off the ventilator. The ventilator was then turned back on and, simultaneously, the animals were treated with either the adrenocorticotropin fragment 1-24 [ACTH-(1-24), 160 microg/kg in a volume of 1 ml/kg i.v.] or an equivalent volume of saline. Nitric oxide (NO)-haemoglobin formation was detected ex vivo in arterial blood by electron spin resonance spectrometry; arterial blood pressure, electrocardiogram (ECG) and electroencephalogram (EEG) were monitored for a 60-min observation period, or until prior death. During asphyxia, there was massive formation of NO (red cell concentrations 40-80 microM), associated with a dramatic fall in mean arterial pressure and pulse pressure, marked bradycardia and ECG signs of ischaemic damage, as well as an isoelectric EEG. Treatment with ACTH-(1-24) produced a prompt (within 15 min) and long-lasting drop in NO blood levels, associated with an almost immediate (within 1 min) restoration of cardiovascular function and with a more gradual recovery of EEG, which became normal after 3040 min; all parameters remained stable throughout the 60-min observation period. In saline-treated rats, on the other hand, there was a further increase in NO blood levels, as detected 3 min after treatment, and all died within 5-8 min. Moreover, pretreatment and treatment with S-methylisothiourea sulphate (SMT, 3 mg/kg i.v.), a relatively specific inhibitor of inducible NO synthase, inhibited NO formation, but did not affect the mortality rate (100% within 5-8 min). The present results provide the first evidence that prolonged asphyxia is associated with high blood concentrations of NO, and that the life-saving effect of melanocortin peptides in severe hypoxic conditions is associated with a complete normalization of NO blood levels. However, the lack of SMT protection in this experimental model seems to rule out the possibility that the ACTH-(1-24)-induced resuscitation is due to an effect on NO overproduction.

Effects of Angiotensin II Type 1 Receptor Blockade on the Systemic Blood Nitric Oxide Dynamics in N.OMEGA.-Nitro-L-Arginine Methyl Ester-Treated Rats

“…nous Hb acts as a natural spin-trapping agent for NO (23); 2) neither oxyhemoglobin nor deoxyhemoglobin produces an EPR signal; and 3) the shapes of the EPR signals of methemoglobin and HbNO are completely different, which enables us to distinguish these spectra. Nonetheless, there were still some difficulties in obtaining a fine HbNO signal because of the existence of paramagnetic compounds that give a strong EPR signal overlapping the same magnetic region as HbNO (24)(25)(26)(27)(28)(29). Therefore, we developed an EPR HbNO signal subtraction method based on subtraction of the EPR spectrum of NO-depleted whole blood from that of each sample.…”

Evaluation of systemic blood NO dynamics by EPR spectroscopy: HbNO as an endogenous index of NO

“…Other EPR signals, such as for ceruloplasmin (g ϭ 2.06) and semiquinone radical (g ϭ 2.00), overlap the magnetic field of HbNO (g Z ϭ 2.01) (5,7,10,13,19,42). Because the basal HbNO level is quite low (M range) (11,25), and its EPR signal overlaps with the strong EPR signal of ceruloplasmin ( Fig.…”

“…However, there were still some difficulties in obtaining a fine HbNO signal, because of existing of paramagnetic compounds that give a strong EPR signal overlapping the same region to HbNO (5,7,10,13,19,42). In the present study, we developed an improved method to detect this HbNO signal in whole blood by EPR spectroscopy.…”