Plasma Histamine Levels Under Hypoxic Stress

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Abstract
Whether the action of hypoxia on pulmonary blood vessels is due to release of a mediator like histamine was studied. Male subjects (30) in the age group 20-30 yr were selected. They were divided into 3 groups with 12 men in each group. The 1st group included those who had previously had high altitude pulmonary edema (POHA). The 2nd group included those who never suffered from POHA in spite of high altitude living for over 2 yr. The 3rd group consisted of men who had never been at a high altitude. Basal arterial plasma histamine levels were estimated in all the subjects. The same estimation was done in samples of blood taken 10 min after hypoxic breathing for each subject. The basal histamine levels were more or less the same in all 3 groups. After hypoxia there was significant rise in plasma histamine levels in all 3 groups. There was no significant difference in the rise in the histamine levels on comparing the values for the 3 groups. The significant rise in plasma histamine levels probably is responsible for the rise in pulmonary vascular resistance. The rise in pulmonary vascular resistance is apparently dependent more on the reactivity of the pulmonary arterioles rather than on the amount of histamine released. Hyperreactivity of the pulmonary vasculature is the factor that determines the degree of vascular constriction and consequent development of POHA.

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