H_2S concentrations in the arterial blood during H_2S administration in relation to its toxicity and effects on breathing

摘要

Our aim was to establish in spontaneously breathing urethane-anesthetized rats, the relationship between the concentrations of H_2S transported in the blood and the corresponding clinical manifestations, i.e., breathing stimulation and inhibition, during and following infusion of NaHS at increasing rates. The gaseous concentration of H_2S (CgH_2S, one-third of the total soluble form) was computed from the continuous determination of H_2S partial pressure in the alveolar gas, while H_2S, both dissolved and combined to hemoglobin, was measured at specific time points by sulfide complexation with monobromobimane (CMBBH_2S). We found that using a potent reducing agent in vitro, H_2S added to the whole blood had little interaction with the plasma proteins, as sulfide appeared to be primarily combined and then oxidized by hemoglobin. In vivo, H_2S was undetectable in the blood in its soluble form in baseline conditions, while CMBBH_2S averaged 0.7 ± 0.5 muM. During NaHS infusion, H_2S was primarily present in nonsoluble form in the arterial blood: CMBBH_2S was about 50 times higher than CgH_2S at the lowest levels of exposure and 5 or 6 times at the levels wherein fatal apnea occurred. CgH_2S averaged only 1.1 ± 0.7 muM when breathing increased, corresponding to a CMBBH_2S of 11.1 ± 5.4 muM. Apnea occurred at CgH_2S above 5.1uM and CMBBH_2S above 25.4 muM. At the cessation of exposure, CMBBH_2S remained elevated, at about 3 times above baseline for at least 15 min. These data provide a frame of reference for studying the putative effects of endogenous H_2S and for testing antidotes against its deadly effects.