Lipopolysaccharide-induced fever in rats prolonged by a needle prick

We studied the effect of an abdominal prick with a needle on LPS-induced fever in freely-moving rats. LPS was injected intraperitoneally by the following 3 methods: 1) through a hypodermic needle pricked into the abdominal cavity, 2) through a catheter chronically indwelt in the abdominal cavity, and 3) through a catheter chronically indwelt in the abdominal cavity immediately after an abdominal prick was made. In the second method, core body temperature (Tb) began to rise about 1 h after the injection, reaching a maximal level at around 2.5 h and decreasing gradually thereafter. In the first and third methods, Tb rose again to make a second peak after making the first peak of fever. This was the same when LPS was injected through a hypodermic needle pricked into the abdominal cavity under restrained condition. These results suggest that the abdominal prick with a needle is responsible for the development of the second peak (or prolongation) of LPS-fever in rats.