The in vitro formation of carbon monoxide in blood.

Abstract

Summary.Earlier observations of an endogenous formation of carbon monoxide in man have been analysed with reference to the possibility that the carbon monoxide is formed in the blood by the breakdown of haemoglobin. The following results were obtained. The COHb concentration of blood calculated from determinations of the CO pressure in alveolar air, agrees with the COHb concentration determined directly from blood. The partial pressure of carbon monoxide in the alveolar air is, however, considerably greater than that of ordinary atmospheric air, which means that carbon monoxide is constantly exhaled during respiration.If blood is incubated at 38o C for 20–24 hours, an increase of 40–165 % can be shown in the COHb concentration, this increase being particularly pronounced after haemolysis. This apparent formation of carbon monoxide in blood is considerably increased at acid or alkaline pH's or by addition of sodium azide.If the blood is shaken with carbon monoxide before incubation at 38o C, the carboxyhaemoglobin concentration after 20 hours is decreased. If sodium azide is added to samples containing 5–30 % COHb. before incubation, the concentration is however increased, and at higher COHb‐concentrations there is a decrease, less than that observed without azide.The formation of carbon monoxide was found to parallel the spontaneous formation of methaemoglobin on alteration of the pH or addition of sodium azide.Addition of ascorbic acid and hydrogen peroxide greatly increases the CO formation. The amount of CO produced corresponds to a conversion of up to 15 per cent of the haemoglobin to COHb, calculated from the original haemoglobin concentrations.The formation of CO seems to be parallel to the breakdown of haemoglobin to choleglobin (verdoglobin). This observation can be explained by the assumption that the opening of the tetra‐pyrrole ring occurs with the liberation of the a‐C‐atom after oxidation to CO.It was possible to demonstrate in one subject that the amounts of CO produced and haemoglobin decomposed bear a quantitative relation of approximately 1 molecule CO: 1 haemin group.