Opposite changes in blood histamine and force expiratory volume during bronchial inhalation challenge.

Lack of in vivo data on blood histamine changes in subjects during induced attacks of asthma prompted serial determinations of blood histamine levels and of the forced expiratory volume of the first second (FEV1) in 2 asthmatic undergoing antigen (house dust) inhalation challenge and in 3 subjected to methacholine inhalation. In 1 of 2 dust-sensitive asthmatics inhaling house dust (10(4) pnu), a prominent histamine spike occurred 5 minutes after challenge termination, coinciding with a fall in FEV1 by about 15%. In the other, blood histamine had risen steeply at 7 minutes, FEV1 not falling, due presumably to increased bronchial tolerance acquired by hyposensitization therapy. In 1 of 3 asthmatics inhaling methacholine, 0.75 cumulative units/5 breaths (c.u.) entailed a blood histamine spike coinciding with a fall in FEV1 by 26%; after return of both variables to control levels, a second histamine rise preceded a second FEV1 fall. In another, a blood histamine spike coinciding with a fall in FEV1 by 19% occurred 6 1/2 minutes after the methacholine increment affording 99.15 c.u. In the third, FEV1 from the outset fell progressively before blood histamine rose steeply, reaching its lowest value (-26%) likewise with 99.15 c.u. The mechanisms and the source(s) of the histamine accounting for its short-lived increases in blood remain to be determined.