Leukocyte-endothelial interactions in environmental hypoxia

Area of Science:

• Physiology
• Pathophysiology
• Altitude Medicine

Background:

• Hypoxia, or low oxygen, rapidly affects microcirculation, increasing leukocyte activity and vascular permeability.
• This response is generalized across various microvascular beds.

Purpose of the Study:

• To investigate the microvascular response to hypoxia and the mechanisms of acclimatization.
• To understand the role of reactive oxygen species (ROS) and nitric oxide (NO) in hypoxia-induced inflammation and resolution.

Main Methods:

• Inducing hypoxia by reducing inspired oxygen partial pressure (PIO2).
• Observing microvascular responses (leukocyte rolling, adherence, emigration, vascular permeability).
• Measuring reactive oxygen species (ROS) and nitric oxide (NO) levels, and assessing the effects of antioxidants and nitric oxide synthase inhibitors.

Main Results:

• Initial hypoxia (PIO2 70 Torr) caused increased leukocyte-endothelial interactions and vascular permeability, linked to a rise in ROS.
• Acclimatization to hypoxia (3 weeks) resolved these responses, even with further PIO2 reduction (50 Torr).
• Acclimatization involved inducible nitric oxide synthase (iNOS) upregulation; iNOS inhibition exacerbated leukocyte-endothelial interactions and ROS.

Conclusions:

• Hypoxia initially disrupts the ROS/NO balance, leading to microvascular inflammation.
• Acclimatization restores the ROS/NO balance, likely through iNOS upregulation, resolving inflammation.
• These findings are relevant to altitude-related illnesses like acute mountain sickness and edema.