OPPOSITE CHANGES IN BLOOD HISTAMINE AND FORCED EXPIRATORY VOLUME DURING BRONCHIAL INHALATION CHALLENGE

Abstract

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 1st s (FEV1) in 2 asthmatics undergoind antigen (house dust) inhalation challenge and in 3 subjected to methacholine inhalation. In 1 of 2 dust-sensitive asthmatics inhaling house dust (104 pnu [protein N units]), a prominent histamine spike occurred 5 min after challenge termination, coinciding with a fall in FEV1 by about 15%. In the other, blood histamine rose steeply at 7 min, 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 2nd histamine rise preceded a 2nd FEV1 fall. In another, a blood histamine spike coinciding with a fall in FEV1 by 19% occurred 6 1/2 min after the methacholine increment affording 99.15 c.u. In the 3rd 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.