Sodium salicylate: alternate mechanism of central antipyretic action in the rat

Ibuprofen in the Management of Viral Infections: The Lesson of COVID-19 for Its Use in a Clinical Setting

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used for the management of fever, pain, and inflammation. However, they have always been considered to have a double-faced role, according to their capacity to manage inflammation but also their possible reduction of immune system response and diagnosis delay. This last point could favor a dramatic increase of viral infection diffusion, possibly leading to a more severe outcome. The advent of severe acute respiratory syndrome coronavirus 2 excluded the use of NSAIDs, particularly ibuprofen, and then indicated this drug as the better NSAID to manage infected outpatients and prevent complications. Several authors described the role of NSAIDs and ibuprofen in preventing cytokine storm and modulating the immune system. However, the development of both adverse drug reactions (i.e., gastrointestinal, renal, hepatic, and cardiovascular) and drug interaction recalled the necessity of prescribing the better NSAID for each patient. In this narrative review, we describe the role of NSAIDs, particularly of ibuprofen, in the management of viral symptoms, suggesting that the NSAID may be chosen considering the characteristics of the patient, the comorbidity, and the polytherapy.

Metabolism, temperature, and ventilation

In mammals and birds, all oxygen used (VO2) must pass through the lungs; hence, some degree of coupling between VO2 and pulmonary ventilation (VE) is highly predictable. Nevertheless, VE is also involved with CO2 elimination, a task that is often in conflict with the convection of O2. In hot or cold conditions, the relationship between VE and VO2 includes the participation of the respiratory apparatus to the control of body temperature and water balance. Some compromise among these tasks is achieved through changes in breathing pattern, uncoupling changes in alveolar ventilation from VE. This article examines primarily the relationship between VE and VO2 under thermal stimuli. In the process, it considers how the relationship is influenced by hypoxia, hypercapnia or changes in metabolic level. The shuffling of tasks in emergency situations illustrates that the constraints on VE-VO2 for the protection of blood gases have ample room for flexibility. However, when other priorities do not interfere with the primary goal of gas exchange, VE follows metabolic rate quite closely. The fact that arterial CO2 remains stable when metabolism is changed by the most diverse circumstances (moderate exercise, cold, cold and exercise combined, variations in body size, caloric intake, age, time of the day, hormones, drugs, etc.) makes it unlikely that VE and metabolism are controlled in parallel by the condition responsible for the metabolic change. Rather, some observations support the view that the gaseous component of metabolic rate, probably CO2, may provide the link between the metabolic level and VE.

Arginine vasopressin, fever and temperature regulation

While central administration of arginine vasopressin (VP) to the non-febrile rat at high doses can cause hypothermia, there is little evidence for a role for endogenous VP in normal thermoregulation. In contrast, VP arising from cell bodies in the bed nucleus of the stria terminalis and innervating the ventral septal areas and possibly the amygdala appears to be an endogenous antipyretic, i.e. a substance capable of reducing fever. As the synthesis of VP in bed nucleus neurons is dependent upon circulating androgens, female rats have much less VP in these cells and their projections than do male rats. In keeping with this, females may make use of VP to a lesser extent than do males to bring about antipyresis. The phenomenon whereby the VP receptor can become sensitized by previous exposure to VP may be responsible for some states of endogenous antipyresis, in which fevers are suppressed through overactivity of the vasopressinergic system. States of endogenous antipyresis can be revealed around the time of parturition in both the neonate and the mother.

Impaired febrile response in mice lacking the prostaglandin E receptor subtype EP3

Fever, a hallmark of disease, is elicited by exogenous pyrogens, that is, cellular components, such as lipopolysaccharide (LPS), of infectious organisms, as well as by non-infectious inflammatory insults. Both stimulate the production of cytokines, such as interleukin (IL)-1beta, that act on the brain as endogenous pyrogens. Fever can be suppressed by aspirin-like anti-inflammatory drugs. As these drugs share the ability to inhibit prostaglandin biosynthesis, it is thought that a prostaglandin is important in fever generation. Prostaglandin E2 (PGE2) may be a neural mediator of fever, but this has been much debated. PGE2 acts by interacting with four subtypes of PGE receptor, the EP1, EP2, EP3 and EP4 receptors. Here we generate mice lacking each of these receptors by homologous recombination. Only mice lacking the EP3 receptor fail to show a febrile response to PGE2 and to either IL-1beta or LPS. Our results establish that PGE2 mediates fever generation in response to both exogenous and endogenous pyrogens by acting at the EP3 receptor.

Neoplastic fever

Neoplastic fever, that is fever arising solely as a manifestation of malignancy, is not as common as was thought but still constitutes a troublesome symptom and is difficult to manage. The mechanism of neoplastic fever production involves cytokines such as tumour necrosis factor (TNF), interleukins 1 and 6 (IL-1, IL-6) and interferon (IFN), produced either by host macrophages in response to tumour, or sometimes by the tumour itself. The cytokines stimulate production of prostaglandins which act on the hypothalamus causing a change in the thermostatic set point. This mechanism is similar to that of infective fever. Paracetamol (acetaminophen) will often only partially lyse neoplastic fever but nonsteroidal anti-inflammatory drugs have been shown to be effective. On the basis of small studies, naproxen has been proposed as a useful test to discriminate between neoplastic and infective fever. If this is so, it must be acting through a pathway hitherto undescribed and specific to neoplastic fever. Other work shows that this group of drugs effectively lyses both types of fever. Therefore larger studies are needed to confirm or refute the "Naproxen test' and neoplastic fever remains a diagnosis of exclusion. In the future, cytokine antagonists may have a role in managing neoplastic fever, but, until their actions are better understood, nonsteroidal anti-inflammatory drugs remain the medication of choice if standard antipyretics have failed.

Alteration of the physiological responses to indomethacin by endotoxin tolerance in the rat: a possible role for central vasopressin

1. Previous studies suggest that arginine vasopressin (AVP) is released into the ventral septal area (VSA) of the rat brain during the antipyresis induced by the cyclo-oxygenase inhibitor indomethacin. In addition, there is evidence for increased AVP transmission in the VSA of animals having a reduced pyretic response following three intravenous injections of bacterial endotoxin (LPS) (endotoxin tolerant). Since ventral septal AVP receptors can also become 'sensitized' following exposure to AVP, we questioned whether the antipyretic action of indomethacin would increase, via an action involving central AVP, if this drug were administered into LPS-tolerant rats. 2. Intraperitoneal indomethacin (7.5 mg kg-1) was effectively antipyretic when administered 2 h after an intravenous challenge with LPS (50 micrograms kg-1) into conscious unrestrained rats. This dose of indomethacin had no effect on the core temperature of non-febrile rats given intravenous 0.9% pyrogen-free saline. 3. Three intravenous injections of LPS over a period of 3 days resulted in rats that were tolerant to the pyrogenic effects of LPS. When indomethacin was administered 2 h following the third LPS injection, a dose-dependent hypothermia was observed. This effect was age dependent, as profound hypothermia was seen in 8 week but not 20 week old rats. 4. A mortality rate of 41% (P = 0.02) was observed within 24 h of indomethacin treatment in 8 week old tolerant rats compared with 0% in 8 week old non-tolerant and 20 week old tolerant rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Fever: causes and consequences

The present review distinguishes pathogenic, neurogenic, and psychogenic fever, but focuses largely on pathogenic fever, the hallmark of infectious disease. The data presented show that a complex cascade of events underlies pathogenic fever, which in broad outline - and with frank disregard of contradictory data - can be described as follows. An invading microorganism releases endotoxin that stimulates macrophages to synthesize a variety of pyrogenic compounds called cytokines. Carried in blood, these cytokines reach the perivascular spaces of the organum vasculosum laminae terminalis (OVLT) and other regions near the brain where they promote the synthesis and release of prostaglandin (PGE2). This prostaglandin then penetrates the blood-brain barrier to evoke the autonomic and behavioral responses characteristic of fever. But then once expressed, fever does not continue unchecked; endogenous antipyretics likely act on the septum to limit the rise in body temperature. The present review also examines fever-resistance in neonates, the blunting of fever in the aged, and the behaviorally induced rise in body temperature following infection in ectotherms. And finally it takes up the question of whether fever enhances immune responsiveness, and through such enhancement contributes to host survival.

The effectiveness of arginine vasopressin and sodium salicylate as antipyretics in the Brattleboro rat

The infusion of either 30 micrograms/microliters (approx. 100 micrograms/kg/h) of sodium salicylate or 10 ng/microliters (10(-5) M) arginine vasopressin within the ventral septal area of the Brattleboro rat brain reduced a centrally induced prostaglandin E1 (PGE1) hyperthermia when compared with infusions of artificial cerebrospinal fluid. Conversely, the infusion of a related peptide, oxytocin (10 ng/microliters (10(-5) M), or 33 ng/kg/h) failed to alter the rise in core temperature following the PGE1 injection. These results suggest that the vasopressin receptors reported to be present in the Brattleboro rat may respond normally to exogenously administered vasopressin, thus allowing for the antipyretic action. Moreover, the antipyretic effects of sodium salicylate suggest that aspirin-like drugs may induce the release of alpha-melanocyte-stimulating hormone which, in turn, attenuates the PGE1-evoked fever. Given recent evidence, however, which suggests that the Brattleboro rat may contain vasopressin both peripherally and within the brain, the antipyretic action of sodium salicylate may be alternatively explained through the endogenous release of vasopressin.