Characteristics of pyrogen fevers are altered in the aged rabbit

Brain eicosanoids and LPS fever: species and age differences

The results of the present study, summarized in Table 2, demonstrate that different species and strains of rodents (rats and mice) and birds (chickens) exhibit rather specific fever response. Systemic administration of LPS caused monophasic elevation in Tb of chickens, biphasic changes in Tb of rats (initial drop followed by an increase in Tb), whereas mice failed to develop hyperthermia and responded by a decreased Tb. The LPS-induced alterations in hypothalamic prostanoid synthesis were also rather species-specific and differ markedly even between the two strains of mice. We failed to find a common direct correlation between LPS-induced changes in Tb and hypothalamic prostanoid production in rodents (rats and mice). This observation is supported by our recent study on age-related changes in fever response in rats, where we found that hypothalami of LPS-treated old and young adult rats produced similar amounts of PGE2 and PGI2, in spite of more pronounced and prolonged hypothermia, and a delayed elevation in Tb of old rats, as compared with young (Fraifeld et al., 1995b). Moreover, the hypothalamus of febrile chickens did not display any detectable activation of PGE2 production, suggesting that PGE2 is not a common central mediator of fever in homeotherms (Fraifeld et al., 1995a). Apparently, the actual body temperature not always reflects the functional state of central thermostat, and increased PGE2 production in hypothalamus would not directly, at least in rodents, lead to body temperature elevation. Furthermore, peripheral effects, including PG-mediated ones, of pyrogens can interfere and even overcome their centrally-mediated effects (Morimoto et al., 1991; Burysek et al., 1993). Previously, we have shown that no additional elevation in hypothalamic PGE2 production occurs in response to doses of LPS over 10 micrograms in rats and 25 micrograms in mice, while the increased doses led to further changes in Tb response (Kaplanski et al., 1993). Morimoto et al. (1991) have considered that PGE2 acts centrally to cause fever and peripherally to cause hypothermia, and, hence, these opposing actions, both being induced by LPS, may act together to determine the final thermoregulatory response. Other possibilities could be related to counterbalance of endogenous antipyretics (Kluger, 1991; Kozak et al., 1995), that may occur not only at the level of thermoregulatory center but also outside the CNS (Klir et al., 1995), and to the existence of PG-independent mechanisms of LPS fever. The latter have been shown for IL-8 (Rothwell et al., 1990; Zampronio et al., 1994) and MIP-1 (Davatelis et al., 1989; Minano et al., 1990; Hayashi et al., 1995; Lopez-Valpuesta and Myers, 1995), which are, apparently, mediated via CRF (Strijbos et al., 1992; Zampronio et al., 1994), and INF-alpha, mediated via the opioid receptor mechanisms (Hori et al., 1991, 1992). However, it has been shown recently that in different species the same pyrogenic cytokines (IL-8) may induced fever via different, PG-independent (in rats; Zampronio et al., 1994) or PG-dependent (in rabbits; Zampronio et al., 1995) mechanisms. It should be noted that fever response is not always accompanied by an elevation in Tb. The final effect of pyrogens on body temperature depends upon the balance between heat production and heat loss, which in turn is highly dependent upon body size and ambient temperature, especially in small animals. Perhaps, the hypothermic response observed in our mice and rats at 22 degrees C may be in part attributed to ambient temperature, which was below a thermoneutral zone. The reduced febrile response is considered, at least in part, to contribute to an increased mortality and prolonged recovery from infections (Kluger, 1986). From this point, it is difficult to suggest whether the hypothermia observed in our mice and rats could be of somewhat adaptive significance. It has been shown that at the ambient temperature of 30 degrees C, Swiss Webster mice can re

Fever in the elderly

Fever in elderly persons is only one clinical presentation that can be used to assist the clinician at suspecting a serious disease, such as an infection. Infections, like all other illnesses in the geriatric patient, may occur with a variety of nonspecific, atypical, nonclassic, and unusual manifestations. The clinician caring for elderly patients should be aware of these nonclassical presentations of infections in this age group. Unexplained change in functional capacity, worsening of mental status, weight loss or failure to thrive, weakness and fatigue, falls, and generalized pain are only some of the clues that may aid the clinician in considering infection in elderly persons. Key concepts of fever in older adults are: Fever generally indicates presence of serious infection, most often caused by bacteria. Fever may be absent in 20%-30% of elderly patients harboring a serious infection. Criteria for fever in elderly patients should also include an elevation of body temperature of at least 2 degrees F from baseline values. FUO in elderly persons is caused by infections (30%-35%), CTD (25%-30%), and malignancies (15%-20%) in the majority of cases.

Effect of different ambient temperature and lipopolysaccharide administration on the circadian rhythm of rectal temperature and hypothalamic PGE2 production in aged male rats

Old and young male rats (22 and 7 months respectively) were exposed to ambient temperatures of 4, 22, 27 and 35 degrees C. The rats' rectal temperatures (RTs) were measured periodically, after exposure to the varying temperatures at different hours during the day. The mean circadian value of RTs in the aged rats was different from that of the young rats. Whereas exposure to low temperatures caused a decrease of 2.0 degrees C in the RTs of the old rats, exposure to heat (35 degrees C) caused an increase of 1 degree C in their RTs. An injection of 200 micrograms (intraperitoneally) of E. coli lipopolysaccharide caused them to experience a long period of hypothermia. Elevation in the RTs after the hypothermic period ended was significantly lower in the old rats. However no significant differences in hypothalamic PGE2 production were to be found between the old and young groups 24 h after pyrogen administration.

Delayed febrile response in old rats is not associated with an inability of hypothalamus to produce prostaglandin E2

E. coli lipopolysaccharide (100 micrograms per rat, i.p.) induced a twofold increase in hypothalamic prostaglandin E2 (PGE2) production both in young adult (8 months) and old (28-30 months) male Wistar rats. It seems that the ability of the hypothalamus to produce PGE2 in response to bacterial endotoxin is not affected with aging, and hence delayed febrile response observed in old rats is not related to hypothalamic PGE2 production.

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.

Impaired febrile responses of aging mice are mediated by endogenous lipocortin-1 (annexin-1)

The mechanisms underlying age-related impairments in febrile responses were investigated in female C57Bl/lcrf-a(t) mice. Injection of norepinephrine, to assess total thermogenic capacity, significantly increased oxygen consumption (VO2) in all age groups, although the responses of the aged mice were significantly reduced. Injection of lipopolysaccharide or murine interleukin-1 beta (mIL-1 beta) significantly increased body temperature and VO2 in the young and adult mice but not in the aged mice. The impaired responses to mIL-1 beta in the aged mice were normalized by either injection of the glucocorticoid receptor antagonist RU-38486 or by injection of an antiserum to lipocortin-1 or its purified immunoglobulin G fraction. Injection of prostaglandin E2 significantly increased VO2 and body temperature in all age groups. Resting plasma corticosterone concentrations were significantly elevated in the aged and adult mice, whereas injection of mIL-1 beta significantly raised plasma corticosterone concentrations in all animals. These findings indicate that the impaired febrile response of aged female C57Bl/lcrf-a(t) mice may be caused by increased concentrations and/or sensitivity to endogenous glucocorticoids. The impaired febrile responses of aged mice appear to be mediated by endogenous lipocortin-1.

Fever response in elderly nursing home residents: are the older truly colder?

OBJECTIVE

To test the hypothesis that many nursing home residents with an apparently blunted fever response (maximum temperature less than 101 degrees F) may actually have a significant change in temperature (delta T greater than or equal to 2.4 degrees F) which is not recognized because of a low baseline temperature.

DESIGN

Retrospective chart review for cases of infection that met specific criteria and for chart-recorded baseline and infection temperatures. Chart-recorded baseline temperatures were prospectively compared with re-measurement of morning temperatures.

SETTING

Nursing Home Care Unit of the VAMC West Los Angeles.

PATIENTS

Random review of 40 residents' charts resulted in the detection of 69 infections among 26 residents over a 20-month period. Fifty randomly selected residents prospectively underwent comparison of chart-determined and actual re-measurement of baseline temperatures.

RESULTS

In 50 randomly selected residents, the mean oral baseline temperature of 97.4 +/- 0.2 (degrees F +/- SEM) closely approximated the mean nurse-recorded measures in the charts (97.6 +/- 0.1). Chart review detected 69 infections among 26 residents, with 53 episodes having a temperature recorded during the infection. The mean maximum temperature (Tmax) during an infection was 101.3 +/- 0.3 (degrees F +/- SEM) but 47% (25/53) of the episodes had a "blunted" fever response (Tmax less than 101 degrees F). Of the 25 "blunted" fevers (Tmax less than 101 degrees F), about one-fourth demonstrated an adequate change in temperature from baseline (delta T greater than or equal to 2.4 degrees F) but failed to reach 101 degrees F because of a low baseline. Most infections (89%) had a Tmax greater than 99 degrees F.

CONCLUSION

Establishing a nursing home patient's basal temperature and monitoring for changes in temperature (delta T greater than 2.4 degrees F) and/or lowering the threshold for recognition of fevers (to 99 degrees or 100 degrees F) in nursing home residents with a change in function should assist in early recognition of infections.