The importance of early microcirculatory changes in the rat colon after exposure to
acetic acid was investigated. Administration of 4%
acetic acid for 15 sec into an exteriorized colonic segment induced a marked, transient (starting 2 min after the challenge with
acetic acid and persisting for 15 min) decrease in the colonic blood flow as estimated by a
laser-Doppler
flowmeter. Four days after
acetic acid administration, a uniform
colitis had developed in the exteriorized colonic segment with a total morphological score (TMS) of 15.1 +/- 0.8,
myeloperoxidase activity (MPO) increased more than threefold, and plasma exudation into the colonic lumen increased sevenfold. Administration of
hydrochloric acid (HCl) with the same pH as the
acetic acid or
sodium acetate (pH 7.0) did not affect colonic blood flow or produce
colitis. Mechanical colonic
ischemia, induced by a controlled increase in the intraluminal pressure, resulted in several pathological features of
colitis with a TMS of 7.3 +/- 0.2, combined with a significant increase in MPO activity. The TMS and MPO were further increased when mechanical colonic
ischemia was combined with HCl or
sodium acetate. Pretreatment with SOD and
catalase 5 or 15 min before
acetic acid administration did not affect the transient
ischemia immediately following
acetic acid administration. However, it partially prevented the development of
colitis. It is concluded that immediate transient
ischemia accompanied by the generation of
oxygen free radicals might be of importance in the pathogenesis of
acetic acid-induced
colitis in the rat.