Estradiol and thermoregulation in adult endotoxemic rats exposed to lipopolysaccharide in neonatal life

Aims: Early life immune challenge has been considered an adaptive defense strategy against potential pathogens when the innate immune system is not completely developed. This study assesses whether neonatal endotoxin challenge alters body temperature response in adult female rats during endotoxemic shock and also, whether ovarian hormones may participate in this response. Methods: Rats were intraperitoneally injected with lipopolysacharide (LPS) or saline at post‐natal day 14, then as adults they were submitted to endotoxemic shock. Results: The LPS injection in adult neonatal Saline rats caused an initial hypothermia, followed by a febrile response. However, neonatal LPS showed an increased hypothermic response and an attenuation of fever. The bilateral ovariectomy abolished the difference in body temperature between the neonatal LPS and saline rats. To determine the dependence of ovarian hormones, ovariectomized rats treated with estradiol cypionate (ECP) restored hypothermia and the suppressed febrile response. However, the same results were not obtained when the animals were supplemented with ECP and medroxyprogesterone acetate (MPA). The neonatal LPS rats displayed a significant reduction in TNF‐α levels and an increase in IL‐10 levels when compared with saline animals. The ECP injection significantly enhanced IL‐10 and suppressed TNF‐α in neonatal LPS, but it did not change the inflammatory response in the saline rats. The ECP + MPA regiment in the neonatal LPS rats reduced TNF‐α, but eliminated IL‐10 stimulation in comparison with the saline group. Conclusion: The present investigation shows that neonatal LPS challenge alters the thermoregulatory response during endotoxemic shock in adulthood and the mechanism for this difference could be mediated by sex hormones, especially estradiol.     

Restoration of normal febrile response to endotoxin in pyrogen-tolerant rabbits by injection with human beta interferon.

Early-phase pyrogen tolerance was induced in rabbits by two consecutive daily injections of 125 ng of endotoxin per kg of body weight. The second injection of the same dose of endotoxin evoked only a monophasic fever with a peak response 1.5 h after the injection; no second peak was observed. The rabbits were released from the tolerance to develop a typical biphasic fever by an injection of 125 ng of endotoxin along with human beta interferon (HuIFN-beta), although the tolerance-inducing amount of endotoxin alone could not. The profile of the febrile response of tolerant rabbits injected with both endotoxin and HuIFN-beta could not be distinguished from that of normal rabbits. There was no essential difference between natural and recombinant HuIFN-beta in breaking tolerance. Heat-stable (70 degrees C, 30 min) endogenous pyrogen or tumor necrosis factor was increased significantly in concentration in the serum of tolerance-broken rabbits. These results suggest that HuIFN-beta stimulates the production of tumor necrosis factor in tolerant rabbits to elicit the second peak of febrile response.     

Modulation of leukocyte-endothelium interaction by nitric oxide synthase inhibitors: effects on leukocyte adhesion in endotoxin-induced uveitis

OBJECTIVE AND DESIGN: To examine the effects of the nitric oxide synthase (NOS) inhibitors aminoguanidine (AG) and L-NAME on leukocyte adhesion in endotoxin-induced uveitis (EIU). MATERIAL: Uveitis was induced in Lewis rats (n = 124) by LPS injection (Salmonella typhimurium). TREATMENT: Rats either (1) did not receive any LPS or other treatments (controls), received (2) only subcutaneous saline injections with LPS administration, (3) a single s.c. dose of AG (100 mg/kg body weight) at the time of LPS administration, (4) a single s.c. injection of AG 8 h after LPS injection, (5) s.c. injections of AG at the time of LPS administration and 8 h after LPS injection or (6) received a single dose of L-NAME (75 mg/kg body weight) at the time of LPS administration. METHODS: Intravital microscopy (IVM) of iris vessels was performed at 2, 4, 8, 16, 24 and 48 h after endotoxin injection. Aqueous humor analysis for protein concentration and cell count was performed after IVM. RESULTS: At 2 h after the induction of uveitis, significantly more rolling leukocytes were detected in the AG and L-NAME-treated group than in untreated EIU (4.8 +/- 0.31 and 9.83 +/- 0.64 vs. 2.85 +/- 0.37%, mean +/- SEM, p < 0.01). However, at 16 h the percentage of rolling leukocytes was significantly reduced in all groups which had received AG (LPS: 8.08 +/- 0.37%; LPS/AG 0 h: 3.78 +/- 0.25%; LPS/AG 8 h: 5.34 +/- 0.3%; LPS/AG 0+8h: 3.86 +/- 0.31%). L-NAME enhanced leukocyte rolling even at 24 h after LPS (12.38 +/- 0.64%). Early treatment of EIU with AG significantly reduced the number of sticking leukocytes at 4, 8 and 24 h (306 +/- 13 vs. 571 +/- 41, 228 +/- 12 vs. 345 +/- 19 and 240 +/- 14 vs. 469 +/- 23 cells/mm2, respectively). L-NAME inhibited LPS-induced sticking of leukocytes at all observed time points and this effect was most pronounced at 24 h (147 +/- 10 vs. 469 +/- 23 cells/mm2). CONCLUSIONS: In EIU, administration of AG or L-NAME causes enhanced leukocyte rolling in the early inflammatory response. However, firm adhesion of leukocytes to the vascular endothelium decreases and this effect prevails, ameliorating leukocyte infiltration.     

Evidence that nitric oxide stimulates feeding in the marsupial Sminthopsis crassicaudata.

Nitric oxide (NO) synthase inhibitors reduce food intake in rodents and chickens, suggesting that NO may stimulate feeding. We used two competitive, non-selective inhibitors of NO synthase (NOS), (NG-monomethyl-L-arginine ester [L-NMMA] and NG-nitro-L-arginine methyl ester [L-NAME]), to evaluate the role of NO mechanisms in the control of food intake in a marsupial model previously used in studies of appetite regulation. Adult male Sminthopsis crassicaudata (n = 11-16, 15 +/- 0.3 g, mean +/- S.E.M.) received L-NMMA (50, 100, 200 and 1000 mg/kg), L-NAME (50, 100 and 200 mg/kg), L-arginine (L-arg) the precursor of NO (1000 and 2000 mg/kg), L-NAME (200 mg/kg) in combination with L-arg (2000 mg/kg), or saline (0.9%). All drugs were administered intraperitoneally after 24 h of food deprivation, after which food was immediately made available ad libitum. Food intake was measured 0, 0.5, 1, 2, 4 and 24 h after treatments. In addition, we studied the effect of acute L-NAME administration on hypothalamic, cortical, hepatic and cardiac NOS activity by quantifying citrulline production. L-NMMA (1000 mg/kg) and L-NAME (100 and 200 mg/kg) suppressed food intake by 25%, 21%, and 30%, respectively, over 24 h after treatments (P < 0.05). L-arg (1000 and 2000 mg/kg) by itself had no significant effect on food intake when compared with saline (P > 0.05). When administered in combination with L-NAME (200 mg/kg), L-arg (2000 mg/kg) reversed L-NAME induced suppression of appetite (P> 0.05). Furthermore, L-NAME (200 mg/kg) significantly decreased hypothalamic (P < 0.01), cortical (P < 0.01) and hepatic (P < 0.03) NOS activity. L-NAME had no effect on cardiac NOS activity (P> 0.05). These data show that peripheral administration of L-NAME has a significant central effect, particularly in brain areas involved in appetite regulation, and suggest in marsupials, as in other mammals and birds, that NO plays a role in the regulation of food intake.     

Estrogen influences stimulated water intake by ovariectomized female rats

To further elucidate the influence of estrogen on water consumption, we examined water intake by adult female rats stimulated by water deprivation, injection of hypertonic saline or injection of isoproterenol (ISOP), a beta-adrenergic agonist that activates the renin-angiotensin system (RAS). Rats were ovariectomized (OVX) then injected with estradiol benzoate (EB; 10 microg/0.1 ml oil) or the oil vehicle (OIL; 0.1 ml) for 2 consecutive days. Twenty-four hours after the second injection, rats were deprived of food and water. On the following day, rats were given water and intake was measured after 2 h. EB significantly decreased water intake compared with that by OIL-treated rats following water deprivation. Two additional groups of adult female rats were OVX and treated with EB or OIL. Forty-eight hours after EB or OIL treatment, rats were injected with hypertonic saline (1 ml of 2 M NaCl) or ISOP (30 microg/kg in 0.15 M saline) and water intake was measured after 2 h. EB significantly attenuated water intake following ISOP but not after hypertonic saline. Finally, we examined plasma sodium concentration (pNa) after hypertonic saline and plasma renin activity (PRA) after ISOP in EB- and OIL-treated rats and found no differences in pNa or PRA. These results suggest that the stimuli for water intake after hypertonic saline and ISOP were comparable in EB- and OIL-treated rats. Taken together, these results raise the possibility that EB attenuation of stimulated water intake is specific to water intake elicited by activation of the RAS.     

Repeated lipopolysaccharide administration produces tolerance to anorexia and fever but not to inhibition of thirst in rat

In 24 h water and food deprived rats, a single lipopolysaccharide treatment (0.25, 0.50 and 1 mg/kg, i.p.) induced inhibition of thirst and hunger as well as fever. Moreover, the same treatment increased serum cytokines, plasma nitrite/nitrate and corticosterone and urinary prostaglandin levels. In another group of 24 h water and food deprived rats, a repeated lipopolysaccharide treatment (0.25, 0. 50 and 1 mg/kg, i.p.), given at 0, 2, 6, 12 and 24 h, induced tolerance to inhibition of food intake and fever, but not to antidipsogenic effect. Moreover, the same repeated treatment stopped the increase in serum cytokines, plasma corticosterone and urinary prostaglandin concentrations and failed to reduce plasma nitrite/nitrate levels. This data, together with the evidence that a pretreatment with N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) (5 and 10 microg per rat) reverses the antidipsogenic effects in lipopolysaccharide tolerant rats, suggests that the persistent reduction of water intake after a repeated lipopolysaccharide treatment is due to the antidipsogenic action of nitric oxide in the brain.     

Inconsistency and possible habituation of CCK-induced satiety

Rats injected daily with cholecystokinin initially inhibited food intake in the first 30 min after injection, but after several days showed an increase in food ingested to an amount that approached their preinjection baseline food intakes and that did not differ from that of rats injected with isotonic saline. This effect occurred with the synthetic C-terminal octapeptide of cholecystokinin and to a lesser extent with injections of natural cholecystokinin extract. It occurred with wet mash and to a lesser extent with liquid diets. When injections were spaced at twice per week, there was an inconsistent response to cholecystokinin but no evidence of habituation. This finding of possible habituation and inconsistent responding to repeated injections of cholecystokinin questions its role as a physiological satiety signal.     

Drinking and eating in rats following chronic atropine administration

Rats which were non-deprived or deprived of food or water were injected daily for 7 days with atropine sulphate (10 mg/kg). The drug period was preceded and followed by 10 days of saline injections. Atropine sulphate caused a decrease in water intake in the 1 hr immediately following injections in all animals, but in non-deprived rats there was a significant increase in water intake in the remaining 23 hr of the day. The latter result corroborated the finding of Soulairac [5] but further shows that the increased water intake was caused by a delayed effect of the drug, and was dependent on the animals having both food and water available ad lib.     

高同型半胱氨酸诱导血管内皮功能障碍促进微循环障碍和微血栓形成

目的：采用蛋氨酸灌胃复制高同型半胱氨酸血症(hyperhomocysteinemia,HHcy)致内皮功能障碍,在此基础上，联合脂多糖（lipopolysaccharide，LPS）和角叉菜胶（carrageenan，Ca）造成大鼠体内广泛微血栓形成，观察血管内皮损伤和功能障碍对大鼠体内微血栓形成的促进作用。方法: ①内皮损伤模型的建立。SD大鼠随机分为对照组（control）、内皮功能障碍组（HHcy）。HHcy组采用蛋氨酸灌胃4周复制HHcy致内皮功能障碍模型，对照组以等量纯净水灌胃。4 周后检测血浆同型半胱氨酸（homocysteine，Hcy）水平，并取大鼠胸主动脉段进行血管舒张功能检测，同时检测血浆一氧化氮（NO）和血管性假血友病因子（von Willebrand factor，vWF）水平，以评价血管内皮功能状况。②Ca/LPS诱导微血栓形成。SD大鼠随机分为对照组（control）、微血栓组（Ca/LPS）、内皮功能障碍加微血栓组（HHcy＋Ca/LPS）。Ca/LPS组大鼠腹腔注射Ca，16 h再腹腔注射LPS。注射LPS 20 h后心脏采血检测凝血功能和血小板计数，镜下观测肠系膜微循环，24 h大鼠颈动脉采血结束实验，检测血浆NO和vWF值。对照组腹腔注射等量生理盐水，检测指标同模型组。HHcy＋Ca/LPS组大鼠经蛋氨酸灌胃持续4周后，再按照上述方法注射Ca/LPS，观察内皮功能障碍对大鼠微循环障碍和微血栓形成的影响。结果： ①蛋氨酸灌胃4周导致HHcy,血浆vWF水平显著升高，NO水平降低，内皮依赖性血管舒张功能显著降低，提示血管内皮功能受损，大鼠内皮功能障碍模型复制成功。②Ca/LPS组肠系膜微循环可见广泛微血栓形成，注射LPS后20 h ，通过检测凝血指标可见血液处于高凝状态。而与之比较，HHcy＋Ca/LPS组微循环障碍进一步加强，血小板计数减少，血浆NO值降低，vWF升高；注射LPS 20 h后可见血液处于继高凝状态之后的消耗性低凝状态。结论： 蛋氨酸灌胃4周导致HHcy,诱导血管内皮功能障碍。联合Ca/ LPS 造模可建立微循环障碍和微血栓形成的动物模型，而内皮功能障碍能加速加重微循环障碍和微血栓形成。     

The role of nitrinergic connections in central cardiovascular responses mediated by physostigmine infused into posterior hypothalamus

In the last few decades, cholinergic connections located into posterior hypothalamus (PH) have been implicated in the central regulation of blood pressure (BP). Here we investigated the role of nitric oxide (NO) in the blood pressure response elicited by infusion of physostigmine into PH of normotensive rats. In freely moving rats, physostigmine (60-200 nM) produced a dose- and time-dependent elevation of BP which was antagonized by the antimuscarinic drug scopolamine (60 nM) and by L-NAME (100 microM), an inhibitor of NO synthase, both infused into the same site. In contrast, L-arginine (L-Arg; 100 microM), the precursor of NO, and glyceryltrinitrate (GTN; 140 nM), an NO donor, infused into the PH did not affect physostigmine-related pressor response. In rats pre-treated with Escherichia coli lipopolisaccharide (LPS; 0.5 microg i.p. 24h beforehand), however, scopolamine, L-Arg and GTN produced a decrease of BP, an effect antagonized by L-NAME. This suggests that NO only slightly modulates physostigmine-related pressor response elicited into PH of LPS-untreated rats. In contrast, the release of large amounts of NO generated by pre-treating rats with LPS, down-regulates cholinergic connections located at the PH, thus contributing in the central dysregulation of BP which can be found when high circulating endotoxin levels may occur.     

Endotoxin tlerance inhibits lipopolysaccharide-initiated acute pulmonary inflammation and lung injury in rats by the mechanism of nuclear factor-kappaB

In this study, the effect of endotoxin tolerance on lipopolysaccharide (LPS)-initiated pulmonary inflammation, the local production of tumour necrosis factor-alpha (TNF-alpha) and the cytokine-induced neutrophil attractant (CINC), as well as the activation of nuclear factor-kappaB (NF-kappaB) and its subunit composition, were examined in vivo. Endotoxin tolerance was reproduced by four consecutive daily intraperitoneal injections of 0.6 mg/kg of Escherichia coli 055:B5 LPS. Compared with control rats, endotoxin-tolerant rats failed to increase the permeability of pulmonary microvascular or recruit neutrophil to lung tissue upon restimulation with 6 mg/kg of LPSs. Pretreatment with LPSs inhibited the protein level of TNF-alpha in bronchoalveolar lavage fluid (BALF) and mRNA expression of CINC in lung tissue in response to subsequent LPS stimulation. These changes were accompanied by the suppression of activation of NF-kappaB, including the low level of total amount of DNA-binding activity and high percentage of non-transactive p50 homodimers. These data demonstrate that endotoxin tolerance can alleviate the LPS-induced acute neutrophilic pulmonary inflammation in rats and can inhibit the proinflammatory cytokines in lung and suggest that endotoxin tolerance might result from the unresponsiveness of NF-kappaB and persistent high percentage of p50 homodimers. Therefore, the phenomenon of endotoxin tolerance might be used as a strategy for the prevention or treatment of LPS-associated acute respiratory distress syndrome in which excessive or dysregulated inflammation leads to acute lung injury.     

Photoperiod alters hypothalamic cytokine gene expression and sickness responses following immune challenge in female Siberian hamsters (Phodopus sungorus)

Rodents that live in changing environments display different immune responses mediated in part by photoperiod (day length) cues. Siberian hamsters maintained in winter-like (short) photoperiods display smaller physiological and behavioral responses to immune challenges as compared with hamsters housed in summer-like (long) photoperiods. We hypothesized that these different response patterns are attributable to altered cytokine production in the hypothalamus in response to photoperiod changes. Female hamsters were housed in long or short days for 10 weeks to induce photoperiodic alterations, then injected with either LPS (a bacterial endotoxin) or saline. Fever and food intake were assessed 3 h post-injection; hypothalami and blood were collected 3, 6, and 12 h post-injection. LPS induced lower fever and reduction in food intake responses in short-day hamsters as compared with long-day hamsters. Additionally, short-day hamsters reduced IL-1beta and Tnfalpha expression in the hypothalamus 6 h after LPS injection, as measured by quantitative RT-PCR. Plasma estradiol concentrations did not differ between long- and short-day hamsters. These data suggest that differences in cytokine production in the hypothalamus may underlie the photoperiod-induced differences in sickness responses, and that these changes are not mediated by estradiol.     

Chronic glucocorticosteroid administration modulates the response of the fibrinolytic system to bacterial lipopolysaccharide

An in vivo rat model was used to study the effect of chronic glucocorticosteroid administration on the response of the fibrinolytic system to lipopolysaccharide (LPS). Male Lewis rats were injected subcutaneously for 30 consecutive days with either saline or saline containing 0.1 μg/g dexamethasone. On the thirty-first day, the rats were challenged with intraperitoneal injections of LPS (0.5 μg/g). Plasma and selected tissues (liver, kidney, heart, lung, muscle, and fat) were removed for analysis at various times after LPS injection. LPS treatment caused a rapid rise in plasma type 1 plasminogen activator inhibitor (PAW) activity in both groups. However, in the dexamethasone-pretreated animals a transient decline in PAI-1 activity was detected at 4 h, coinciding with a transient increase in plasma tissue plasminogen activator (t-PA) activity and a marked elevation of t-PA messenger RNA (mRNA) levels in the lung. Plasma t-PA activity returned below basal levels by 8 h and did not differ between the two groups at later times. At 24h, PAI-1 activity remained significantly elevated in the dexamethasone-pretreated rats while declining in the saline-pretreated rats. A greater induction of PAI-1 mRNA was evident in the dexamethasone-pretreated rats in all six tissues examined. Notably, a 3-fold greater increase in PAI-1 mRNA was detected in the liver at 24h, corresponding with the sustained elevation in plasma PAI-1 activity at this time. Collectively, these data suggest that chronic glucocorticosteroid treatment potentiates the induction of both t-PA and PAI-1 gene expression by LPS, resulting in an initial transient increase in plasma t-PA activity followed by a more sustained elevation in plasma PAI-1 activity.     

Feeding after recovery from 2-deoxyglucose injection: cerebral and peripheral factors

Rats increased food intake 6 h after peripheral and intracerebroventricular injections of 2-deoxy-D-glucose (2-DG) when plasma glucose concentrations had returned to normal from elevated levels. Rats with adrenal demedullation did not become hyperglycemic after injection of 2-DG and increased food intake more than normal animals after peripheral, but not ventricular, injections of 2-DG. Peripheral injections of 2-DG inhibited gastric emptying in normal, but not adrenal demedullated, rats. Intravenous infusions of epinephrine into normal rats, which mimicked some of the physiological effects of peripheral 2-DG injection, did not increase food intake. The results indicate that a prior disruption of cerebral metabolism is sufficient to elicit feeding in the absence of an adrenomedullary response and that increased gastric fill may restrain the increase in food intake produced by a previous cerebral emergency.     

Interleukin-6 and leptin mediate lipopolysaccharide-induced fever and sickness behavior

Pro-inflammatory cytokines, interleukin (IL)-1beta, IL-6 and tumor necrosis factor-alpha (TNF-alpha) synthesized by activated macrophages and monocytes in response to administration of lipopolysaccharide (LPS), are considered important mediators of fever and sickness behavior. We administered rat-specific antisera for TNF-alpha, IL-1beta, IL-6 and leptin, to determine the involvement of peripherally released cytokines in LPS-induced fever and sickness behavior, measured as suppression of voluntary wheel-running and food intake. Male Sprague-Dawley rats (approximately 200 g) selected for their predisposition to spontaneously run on running wheels were anaesthetized with a combination of ketamine hydrochloride (80 mg/kg i.m.) and xylazine (4 mg/kg i.m.) and implanted intra-abdominally with temperature-sensitive radiotelemeters. Rats were injected intraperitoneally with anti-rat sera to one of the following, TNF-alpha, IL-1beta, IL-6 or leptin or with pre-immune sheep serum, followed by a subcutaneous injection of either LPS (250 microg/kg) or sterile saline. Lipopolysaccharide administration induced a approximately 1.3 (0.2) degrees C fever lasting approximately 10 h and reduced voluntary running by 93 (8.6)% and food intake by 51 (21.3)% compared to the saline response (ANOVA, P<0.05). Injection of anti-IL-6 serum or anti-leptin serum abolished the LPS-induced fever, anti-TNF-alpha serum affected only the early phase of fever and anti-IL-1beta serum had no effect on fever (ANOVA, P<0.05). LPS-induced suppression of voluntary running and food intake were attenuated in rats receiving anti-IL-6 serum, while the decrease in food intake was totally abolished in rats receiving anti-leptin serum (ANOVA, P<0.05). Injection of anti-TNF-alpha or anti-IL-1beta serum had no effect on LPS-induced sickness behavior. Peripherally released IL-6 and leptin therefore appear to be important in regulating LPS-induced fever and sickness behavior.     

Contingent suppression of tolerance to the "anorexigenic" effect of haloperidol

Whether tolerance develops to the "anorexia" induced by haloperidol (HAL) was determined. Rats were given HAL (2.5 or 5 mg/kg) either before or after access to milk for 53 days. Controls were given injections of saline. On Day 54, when all groups received pretest injections of the drug, only rats previously given posttest injections of HAL were tolerant. The absence of tolerance in rats previously given pretest injections suggests that tolerance is suppressed when rats are given access to food in the drugged state. It is concluded that tolerance develops to HAL as a result of pharmacological exposure but is suppressed by the "anhedonic" effect of the drug. The relevance of these findings to the role of reinforcement in behavioral tolerance is briefly discussed.     

Prostaglandins and food intake of rats: A component of energy balance regulation?

Modulation of food intake by signals arising in adipose tissue has been an important component of theories concerning energy balance regulation. Our experiments tested the effects of some prostaglandins (PG) which are produced in adipose tissue, on food and water intakes in rats. Rats were injected intrahypothalamically with 1 μg of either PGE₁ or PGB₁ in 1 μl bilaterally prior to a 2-hr daily meal. PGE₁, but not PGB₁, reduced food intake of the rats in groups with lateral hypothalamic (LH) and anterior commissure (AC) cannulas, but did not reduce food intake in groups with perifornical hypothalamic (PFH) or mammillary body (MB) cannulas. Water intake was reduced in all groups injected with PGE₁ except the LH and MB groups. Anterior and medial hypothalamic groups showed a sustained 2°C rise in rectal temperature following injections of PGE₁. Subcutaneous injections of PGE₁ reduced food intake of three different groups of rats at different levels of adiposity. We hypothesize that some PG's may be components of a signal relating fat depots and energy balance regulation.     

The role of tumor necrosis factor (TNF) in the febrile and metabolic responses of rats to intraperitoneal injection of a high dose of lipopolysaccharide

The role of tumor necrosis factor (TNF) in the febrile and metabolic responses of rats to intraperitoneal injection of a high dose of lipopolysaccharide Injection of a high dose of lipopolysaccharide (LPS) induces a septic-shock-like state, which can be accompanied by phases of hypothermia and phases of fever. In the present study we monitored body core temperature and locomotor activity, both by remote radiotelemetry, as well as changes in food intake, body mass and water intake for 3 days after an intraperitoneal (i.p.) injection of a high dose of LPS (5 mg/kg) along with sterile 0.9% saline or a neutralizing form of the soluble tumor necrosis factor (TNF) type 1 receptor (referred to as TNF-binding protein, TNF bp). Intraperitoneal injection of LPS rapidly induced high concentrations of TNF in the plasma and peritoneal lavage fluid. TNF was undetectable in the plasma and peritoneal lavage fluid of animals co-injected with LPS and TNF bp, implying neutralization of peripheral bioactive TNF. Administration of LPS induced hypothermia by about 1.5 degrees C, which lasted for 5 h after injection. During the light-time periods of days 2 and 3 after injection, the rats developed a robust fever. Treatment with TNF bp resulted in a faster recovery from the LPS-induced hypothermia so that the rats developed a pronounced fever on the day of injection. Locomotor activity during night-time periods was suppressed in LPS-treated animals. The LPS-induced depression of night-time activity was not antagonized by co-injection of TNF bp. On day 1 after the injection of LPS, food intake reduced to virtually zero, water intake fell to about 30% of the control value and body mass dropped by 25 g (about 10% of total body mass). With the exception of body mass, these variables recovered slowly during days 2 and 3 after LPS injection, but did not reach the control values. The LPS-induced decreases in food intake, body mass and water intake were significantly attenuated by the treatment with TNF bp. These results confirm that TNF contributes significantly to the rats' responses to intraperitoneal injection of a high dose of LPS. The fact that treatment with TNF bp accelerated and improved the rats' ability to develop a febrile response supports the view that the fever is beneficial, since all other metabolic responses measured in this study were normalized more effectively in those rats that developed a faster and more pronounced increase in body temperature.     

The inhibition of nitric oxide synthase suppresses LPS- and psychological-stress-induced fever in rats

The purpose of this study was to assess the effects of a non-selective nitric oxide synthase (NOS) inhibitor on changes in fever response due to injection of lipopolysaccharide (LPS) or on stress fever caused by exposure to an open field in freely moving biotelemetered rats. N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of all NOS-isoforms, was injected intraperitoneally (ip) at a dose of 50 mg/kg just before intraperitoneal injection of LPS at a dose of 50 microg/kg or exposure to open field. L-NAME at a dose of 50 mg/kg had no effect on normal day-time body temperature (T(b)) and normal night-time T(b). The same dose of L-NAME administered intraperitoneally caused a significant attenuation of LPS-induced fever. The thermal index calculated for rats pretreated with L-NAME and injected with LPS was reduced by approximately 75% compared to that calculated for saline-pretreated and LPS-injected rats. To examine the effect of NOS inhibition on psychological-stress-induced elevation in T(b), rats were injected intraperitoneally with L-NAME and then immediately exposed to open field for 60 min. After exposure to the open field, rats not treated with NOS inhibitor responded with a rapid rise in T(b), and it was accompanied with an increase of motor activity. L-NAME significantly suppressed the stress fever without any effect on changes in motor activity. Presented data provide clear evidence that NO formation is involved in LPS- and psychological-stress-induced fevers in rats.     

Inhibition of nitric oxide synthase within the medial preoptic area impairs pup retrieval in lactating rats

Central suppression of nitric oxide (NO) production by administering 250 microg of Nitro-superw--subL-Argenine Methyl Ether (L-NAME), an inhibitor of NO synthase, into the 3rd ventricle disrupts both pup retrieval and maternal aggression in postpartum rats. In these studies, the authors examined the ability of varying doses of L-NAME to produce these effects on maternal behavior. Doses of L-NAME that were shown to be ineffective when injected into the 3rd ventricle were administered bilaterally into the medial preoptic area (MPOA) of rats on Day 4 postpartum. To assess the specificity of L-NAME's effect within the MPOA, the authors bilaterally injected Nitro-superw--subD-Argenine Methyl Ether (D-NAME), an inactive isomer of L-NAME, into the MPOA. When administered intracerebroventricularly, the 2 highest doses of L-NAME used, 250 microg and 200 microg, disrupted retrieval behavior and maternal aggression. Bilateral injections of L-NAME into the MPOA at doses of 20 microg and 40 microg/side also disrupted pup retrieval, and D-NAME injections into the MPOA had no effect on the maternal behaviors measured. All rats in these experiments showed normal maternal behavior 24 hr after drug administration. These results suggest that NO acts within the MPOA to facilitate retrieval behavior.