Role of prostaglandin E2 and indomethacin in the febrile response of pigeons

Intravenous (i.v.) injection of 10 microg/kg Escherichia coli lipopolysaccharide (LPS), applied at 13:00, evoked in pigeons a biphasic rise of core temperature (T(core)), so that LPS induced with a latency of 30 min first a decrease of T(core), and 90 min after LPS, T(core) increased, obtaining maximum values from 18:00 to 20:00. Prostaglandins have been considered to be importantly involved in fevers in mammals. To investigate an involvement of prostaglandins in the cyclic variations of T(core) in birds, pigeons were injected i.v. with either 10 mg/kg indomethacin (INDO) or 100 mg/kg aspirin, or they were treated with intracerebroventricular (i.c.v.) injections of 100 microg/kg INDO at various times before or after LPS. When INDO or aspirin was i.v. injected 30 or 15 min before LPS, it diminished the initial decrease of T(core) by more than 50%, whereas the i.v. injection of these drugs 2 and 4 h after LPS did not affect the febrile rise of T(core). i.c.v. injections of INDO given either before or after LPS neither influenced the initial drop of T(core) nor the following febrile hyperthermia. Both the i.v. injection of 1 mg/kg prostaglandin E(2) (PGE(2)) and the i.c.v. injection of 1 microg/kg PGE(2) lowered T(core). Our observations suggest that prostaglandins are not involved in the febrile elevation of T(core) in pigeons, but appear to participate in the decrease of T(core), which shortly follows the i.v. injection of LPS. This initial drop of T(core) following LPS may be caused by a peripheral action of prostaglandins because it was not influenced by the i.c.v. injection of indomethacin.