Increased plasma level of platelet-activating factor (PAF) and decreased serum PAF acetylhydrolase (PAFAH) activity in adults with bronchial asthma.

We evaluated the plasma level of platelet-activating factor (PAF), a chemical mediator that induces various symptoms of bronchial asthma, and the activity of serum PAF acetylhydrolase (PAFAH), an enzyme that specifically inactivates PAF, in adults with bronchial asthma. Measurements were made by radioimmunoassay of samples obtained from 137 adult asthmatic patients (137 cases examined in remission and from among these 41 cases were also measured at the time of an asthmatic attack) 59 adult patients with untreated pulmonary tuberculosis and 106 healthy adult volunteers. It was demonstrated that the plasma PAF level was markedly higher and the serum PAFAH activity markedly lower in the asthmatic patients, both in remission and at the time of asthmatic attack, than in the healthy volunteers. The plasma PAF level was more closely associated with asthma both in remission and at the time of asthmatic attack than with pulmonary tuberculosis, whereas there was no significant difference in the serum PAFAH activity between the two diseases. The low serum PAFAH activity in the asthmatic patients may have been due to saturation as a result of continuous reaction to the increased plasma PAF level in those patients.