Inhaled [13N]nitric oxide: a positron emission tomography (PET) study

Area of Science:

• Nuclear medicine
• Pulmonary physiology
• Pharmacokinetics

Background:

• Nitric oxide (NO) plays a crucial role in cardiovascular and respiratory regulation.
• Understanding the in vivo distribution and kinetics of inhaled NO is essential for its therapeutic applications.
• Previous studies have limited data on inhaled NO uptake by lung tissue.

Purpose of the Study:

• To investigate the distribution and kinetics of inhaled nitric oxide (NO) in anesthetized dogs using positron emission tomography (PET).
• To differentiate NO uptake by lung tissue from simple gas washout.
• To identify the metabolic products of NO in plasma.

Main Methods:

• Positron emission tomography (PET) imaging was employed.
• Nitric oxide radiolabeled with nitrogen-13 (¹³N-NO) was inhaled by anesthetized dogs.
• The washout kinetics of ¹³N-NO were compared to those of ¹³N-nitrogen gas.
• Radioactivity in plasma was analyzed to determine metabolic products.

Main Results:

• Inhaled ¹³N-NO exhibited a significantly slower washout from the lungs compared to ¹³N-nitrogen gas.
• This slower washout indicates substantial uptake of NO by lung tissue.
• The radioactivity detected in plasma was primarily in the form of ¹³N-nitrate.
• The administered NO concentration was below the threshold for significant vasorelaxation.

Conclusions:

• Inhaled nitric oxide is significantly taken up by lung tissue, not merely exhaled.
• The primary circulating metabolite of inhaled NO in this model is nitrate.
• The study provides valuable insights into the fate of inhaled NO in the lungs, relevant for respiratory medicine.