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

Intravenous (I.V.) injection of 10 mug/ 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 90min 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 mug/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 mug/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.