AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 6 1358-R1363, Copyright © 1991 by American Physiological Society
Role of gram-negative and gram-positive gastrointestinal flora in temperature regulation of mice
C. A. Conn, B. Franklin, R. Freter and M. J. Kluger
Department of Physiology, University of Michigan Medical School, Ann Arbor 48109.
An earlier study showed that the presence of gut flora elevates body
temperature of mice and rats. In these experiments, we questioned whether
the signal coming from the gut was endotoxin from gram-negative (Gm-)
bacteria or some signal derived from gram-positive (Gm+) microorganisms. To
test the idea that endotoxin is responsible for the effects of flora, we
compared the temperature of the endotoxin-resistant mouse (C3H/HeJ) with
that of endotoxin-sensitive strains of mice (C3H/SnJ and C3H/HeN).
Temperature of C3H/HeJ was not different from that of C3H/SnJ or C3H/HeN
during the light period but was significantly lower during the later hours
of the dark period. We speculated that, if endotoxin leaking across the gut
wall were responsible for elevating temperature, then reduction of gut
flora with nonabsorbable antibiotics would depress the temperature of the
endotoxin-sensitive mice more than that of the endotoxin-resistant mice.
Because antibiotics lowered the temperature of both strains of mice to the
same extent, the signal coming from the gut is unlikely to be endotoxin. To
test whether Gm+ flora can be responsible for elevating temperature, we
inoculated one group of germfree mice with Gm+ organisms. Their mean
temperature was significantly higher than that of mice that remained
germfree. Cecectomy had no effect on temperature, indicating that the
special properties of the germfree cecum were not involved in lowering the
temperature of germfree mice. These data support the hypotheses that Gm+
organisms are a major source of the stimulatory effect of flora on normal
body temperature and that the presence of Gm- organisms is unnecessary.
