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Updated: Jul 22, 2026
Isolated Lung Perfusion System in the Rabbit Model
Published on: July 15, 2021
Oxygen dependency of monoamine oxidase activity in the intact lung
S H Audi1, C A Dawson, S B Ahlf
1Department of Biomedical Engineering, Marquette University, Milwaukee 53201-1881, USA. audis@marquette.edu
Abstract:
Hydrogen peroxide generated by monoamine oxidase (MAO)-mediated deamination of biogenic amines has been implicated in cell signaling and oxidative injury. Because the pulmonary endothelium is a site of metabolism of monoamines present in the venous return, this brings into question a role for MAO in hyperoxic lung injury. The objective of this study was to evaluate the O(2) dependency of the MAO reaction in the lung. To this end, we measured the pulmonary venous effluent concentrations of the MAO substrate [(14)C]phenylethylamine and its metabolite [(14)C]phenylacetic acid after the bolus injection of either phenylethylamine or phenylacetic acid into the pulmonary artery of perfused rabbit lungs over a range of PO(2) values from 16 to 518 Torr. The apparent Michaelis constant for O(2) was approximately 18 microM, which is more than an order of magnitude less that measured for purified MAO. The results suggest a minimal influence of high O(2) on MAO activity in the normal lung and demonstrate the importance of measuring reaction kinetics in the intact organ.
Insights
Monoamine oxidase (MAO) activity in the lung is minimally affected by high oxygen levels. This study investigated MAO
Area of Science:
- Biochemistry and Physiology
- Pulmonary Medicine
- Oxidative Stress Research
Background:
- Hydrogen peroxide from monoamine oxidase (MAO) activity is linked to cell signaling and oxidative injury.
- The pulmonary endothelium metabolizes biogenic amines, suggesting a potential role for MAO in hyperoxic lung injury.
Purpose of the Study:
- To investigate the oxygen (O2) dependency of monoamine oxidase (MAO) activity within the lung.
- To determine if MAO contributes to hyperoxic lung injury.
Main Methods:
- Perfused rabbit lungs were used to measure MAO substrate and metabolite concentrations.
- Phenylethylamine or phenylacetic acid was injected into the pulmonary artery across a range of oxygen partial pressures (PO2).
- Kinetic analysis was performed to determine the Michaelis constant for O2.
Main Results:
- The apparent Michaelis constant for O2 in the lung was approximately 18 microM.
- This value is significantly lower than that observed for purified MAO.
- High oxygen levels demonstrated a minimal influence on MAO activity in the intact lung.
Conclusions:
- MAO activity in the normal lung is not significantly influenced by high oxygen concentrations.
- These findings highlight the importance of studying enzyme kinetics within the context of the intact organ.
- The direct role of MAO in hyperoxic lung injury may be limited under normal physiological conditions.
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