The relationship between hypothalamic prostaglandin E2 or leukotrienes and the body temperature response to lipopolysaccharide in different murine strains

Central leukotrienes modulate fever tolerance to LPS in rats

Leukotrienes mediate several inflammatory events such as neutrophil chemoattraction, leukocyte adhesion, and central-release of cytokines and fever. However, there is no information available about their putative role in lipopolysaccharide (LPS) tolerance. The rational of the present study was to find out if central leukotrienes are involved in the development of LPS tolerance. Thus, we inhibited central leukotriene synthesis in tolerant rats using a pharmacological tool, i.e., a selective inhibitor of leukotriene synthesis MK-886 injected into the third ventricle (3V) of rats. Body core temperature (Tb) was measured using a datalogger placed inside the abdominal cavity. A low-dose of LPS (100 μg/kg ip) was given for 4 consecutive days to induce LPS tolerance. At day 4, rats received a microinjection of MK-886 into the 3V immediately before LPS, whereas control groups were treated with vehicle (saline). We observed that LPS failed to induce plasma cytokines surges, increased hypothalamic PGE₂ levels and fever 3 days post LPS treatment, aptly characterizing the tolerance. When MK-886 was given to control rats treated with saline, no significant change in Tb was observed. However, a full LPS-induced fever was observed in tolerant rats pretreated with MK-886, which was associated with an enhancement in the hypothalamic PGE₂ levels, that were not accompanied by plasma cytokines (IL-1β, and IL-6) and PGE₂ surges. These data are consistent with the notion that central leukotrienes play a role in fever tolerance to LPS.

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.

Differential sensitivities of pyrogenic chemokine fevers to cyclooxygenase isozymes antibodies

It has been proposed that prostaglandin (PG)E(2) production via a process catalyzed by the inducible isoform of cyclooxygenase (COX)-2 and activation of specific PGE(2) receptor subtypes within the preoptic/anterior hypothalamus (AH/POA) is the last step and unique pathway in the induction of a fever. However, many data support the existence of a PG-independent pathway. That is, other more rapid mechanisms, which involve the constitutive COX-1 isozyme, may be more critical for a PG-dependent fever. Thus, we examined the role of both COX isoforms in the AH/POA in fevers induced by macrophage inflammatory protein (MIP)-1beta, a PG-independent pyrogen, and RANTES (regulated on activation, normal T-cells expressed and secreted), a PG-dependent pyrogen. In freely moving rats, two independent polyclonal antibodies were used which neutralize COX-1 and COX-2. The microinjection of either MIP-1beta or RANTES into the pyrogen-sensitive region of the AH/POA induced an intense fever of rapid onset. Peripheral pretreatment with an antipyretic dose of dexamethasone which prevents COX-2 expression, or the microinjections into the AH/POA of either anti-COX-1 or anti-COX-2, blocked the febrile response induced by RANTES but not that induced by MIP-1beta. These results provide strong evidence for the existence of rapid mechanisms in the AH/POA which involve both COX isozymes during the fever induced by RANTES, and further support the existence of an alternative PG-independent pathway in the febrile response.

The center for multidisciplinary research in aging (CMRA) at Ben Gurion University of the Negev in Israel

The Center for Multidisciplinary Research in Aging (CMRA) was established at Ben Gurion University of the Negev (BGU) in Beer Sheva in 2000, to promote research in the different disciplines of gerontology and geriatrics. It benefits from the special features of that university compared to other academic institutions in Israel and from the regional uniqueness of its location, in the southern part of Israel. CMRA serves as a comprehensive outreach unit for collaborative projects, as well as training programs and organization of professional meetings on aging.

Molecular mechanisms of fever and endogenous antipyresis

This review summarizes recent studies on endogenous antipyretic mechanisms. Fever is the result of a balance between pyrogenic and cryogenic cytokines and hormones. Although there is considerable evidence that fever evolved as a host defense response, it is important that the rise in body temperature not be too high. Many endogenous cryogens or antipyretics that limit the rise in body temperature have been identified during the last 25 years. These include alpha-MSH, arginine vasopressin, glucocorticoids, TNF (under certain circumstances), and IL-10. Most recently, evidence has accumulated that cytochrome P-450 (P-450), part of the alternative pathway for arachidonic acid metabolism, plays an important role in reduction of fever and inflammation. Supporting a role for P-450 in endogenous antipyresis and antiinflammation includes evidence that (1) inducers of P-450 reduce fever, (2) inhibitors of P-450 cause a larger fever, (3) and P-450 arachidonic acid metabolites reduce fever.