Elevation of plasma ACTH concentration in rabbits made febrile by systemic injection of bacterial endotoxin

Optimization of ultrasonic-assisted ultrafiltration process for removing bacterial endotoxin from diammonium glycyrrhizinate using response surface methodology

Ultrasonic-assisted ultrafiltration (UAU) removing bacterial endotoxin from diammonium glycyrrhizinate, was firstly applied to surfactant separation. Separation efficiency was related with four variables, including ultrafiltration molecular weight cut off (MWCO), ultrasonic power, concentration and pH. The SCQ-9200E ultrasonic system was provided for the study with adjustable ultrasonic power 80 W to 800 W, and the ultrasonic frequency was 40 KHz. On the basis of response surface methodology (RSM), the optimal separation conditions were determined to be the ultrafiltration MWCO as 10 kDa, the ultrasonic power as 570 W, diammonium glycyrrhizinate concentration as 150.00 μg/mL and the pH as 4.70. The experimental rejection of bacterial endotoxin was 94.08%, meanwhile the transmittance of diammonium glycyrrhizinate was 93.65%. Based on the ultrasonic power, solution volume, and ultrasonic container size, the experiments with UAU at different power intensities showed that ultrasonic at a power intensity of 57 W/L and the power density of 0.32 W/cm² could solve the separation contradiction between diammonium glycyrrhizinate and bacterial endotoxin. This study indicated that UAU could be an innovation in ultrasonic separation fields, and had a vast range of prospects for making use in pharmaceutical preparation area.

Effect of natriuretic peptide receptor antagonist on lipopolysaccharide-induced fever in rats: is natriuretic peptide an endogenous antipyretic?

We investigated whether natriuretic peptide (NP) acts as an endogenous antipyretic inside and/or outside the blood-brain barrier in rats made febrile by systemic administration of bacterial endotoxin (lipopolysaccharide; LPS). Intravenous (i.v.) injection of LPS induced a triphasic fever, the second phase of which was significantly enhanced by an i.v. injection of the NP receptor (A-type and B-type) antagonist HS-142-1, a glucose-caproic acid polymer. In contrast, the same antagonist (i.v.) had no effect on the fever induced by i.v. injection of interleukin (IL)-1beta. An i.v. administration of HS-142-1 enhanced the LPS (i.v.)-induced IL-1beta response in the rat spleen. An i.v. treatment with atrial NP (ANP) significantly attenuated the second phase of the LPS-induced fever. On the other hand, i.c.v. injection of the above-mentioned NP receptor antagonist resulted in an augmentation of the third phase of the fever induced by i.v. administration of LPS, the same phase that was attenuated by ANP given i.c.v. When given intracerebro-ventricularly (i.c.v.), the antagonist had no effect on the fever induced by i.v. IL-1beta. Finally, the fever induced by i.c.v. injection of LPS was not affected even by an i.c.v. administration of the antagonist. These results suggest that the production of pyrogenic cytokines (such as IL-1beta) that follows i.v. LPS injection may be inhibited by NP acting outside the blood-brain barrier, leading to an inhibition of the fever. In contrast, inside the blood-brain barrier NP may inhibit cytokine-independent mechanisms present within the rat brain that mediate LPS (i.v.)-induced fever.

Are transcription factors NF-κB and AP-1 involved in the ANG II-stimulated production of proinflammatory cytokines induced by LPS in dehydrated rats?

We recently reported an involvement of ANG II and the ANG II type 1 (AT1) receptor in the hepatic expression of IL-1β induced in dehydrated rats by LPS. Here, we first confirmed that ANG II and AT1 receptors contribute to the LPS-induced increase in the splenic concentration of IL-1β in dehydrated rats. We then investigated whether ANG II contributes to IL-1 production through a modulating effect on the activation of proinflammatory transcription factors (NF-κB and AP-1) that is induced in the dehydrated rat's liver and spleen by intravenous injection of LPS. Surprisingly, LPS markedly increased the hepatic activation of NF-κB, an effect that was significantly enhanced (rather than reduced) by pretreatment with an ANG-converting-enzyme (ACE) inhibitor or AT1-receptor antagonist. Furthermore, the same ACE inhibitor and AT1-receptor antagonist each increased the resting NF-κB activity in the liver and spleen, although they had no effect on the LPS-induced splenic expression of NF-κB. Both hepatic and splenic AP-1 expressions were enhanced by LPS. This response was significantly augmented by pretreatment with the AT1-receptor antagonist (but not with the ACE inhibitor) in the spleen, while in the liver, neither drug had any effect. These results suggest that the endogenous ANG II or AT1 receptor suppresses the activation of hepatic or splenic transcription factors in dehydrated rats given LPS. Our results seem not to support the idea that NF-κB and AP-1 play key roles in the ANG II-induced enhancement of the production of proinflammatory cytokines that is induced by LPS in dehydrated rats.

Site and mechanism of action of dynorphin A-(1-13) and N-methyl-D-aspartate on ACTH release in fetal sheep

Dynorphin A (Dyn A) stimulates the release of ACTH in fetal sheep, a response that involves N-methyl-D-aspartate (NMDA) receptors but not the secretogogues corticotropin-releasing hormone or arginine vasopressin. We now find that neither Dyn A-(1-13) (0.5 mg/kg, i.v.) nor NMDA (4 mg/kg, i.v.) elicits ACTH release in postnatal lambs. This led us to hypothesize that Dyn A-(1-13) and NMDA might act to release placental ACTH. However, the ability of Dyn A-(1-13), NMDA, and the kappa-opioid receptor agonist U-50488H (1 mg/kg, i.v.) to release ACTH was lost after either fetal hypophysectomy (n = 4) or hypothalamo-pituitary disconnection (n = 4). These results indicate that neither the placenta nor the fetal pituitary is the site of action for these agonists and suggest a hypothalamic or suprahypothalamic site of action. Furthermore, the release of ACTH by Dyn A-(1-13) and NMDA was abolished after pretreatment with indomethacin, suggesting that they might cause the release of a prostanoid, possibly from the placenta, that subsequently acts at the hypothalamus or serves as a permissive factor in the action of Dyn A-(1-13) and NMDA at the hypothalamus.

Impact of environmental temperature on response of neonatal pigs to an endotoxin challenge

OBJECTIVE

To evaluate the effect of various environmental temperatures (ET) on the ability of neonatal pigs to cope with an endotoxin challenge.

ANIMALS

28 crossbred male pigs that were 24 hours old.

PROCEDURE

At 24 hours of age, pigs were placed in environmentally controlled chambers maintained at 18 or 34 C (14 pigs/ET). Rectal temperatures (RT) were recorded at 15-minute intervals for 3 hours following an IP injection of 0.9% NaCl (7 control pigs/ET) or lipopolysaccharide (LPS; 150 microg/kg of body weight; 7 LPS-treated pigs/ET). Tissue specimens and blood samples were collected following the 3-hour challenge period.

RESULTS

LPS-treated pigs exposed to 18 C had a period of hypothermia whereas RT for LPS-treated pigs at 34 C did not differ from control pigs. The LPS-treated pigs maintained at 18 C lost the most body weight during the 3-hour period and also had the greatest increase in serum cortisol concentration. Serum prolactin (PRL) concentration was decreased in pigs at 18 C, compared with pigs at 34 C. Challenge with LPS resulted in an increase in serum PRL concentration at 18 C but had no effect on serum PRL at 34 C. Challenge with LPS resulted in an increase in expression of tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6 receptor mRNA in the hypothalamus.

CONCLUSIONS AND CLINICAL RELEVANCE

Exposure to a cold ET can inhibit the ability of neonatal pigs to cope with an exogenous endotoxin challenge. When combined, cold stress and exposure to exogenous endotoxin induces a rapid and potentially dangerous loss of body temperature in neonatal pigs.

Angiotensin AT1 receptors in the preoptic area negatively modulate the cardiovascular and ACTH responses induced in rats by intrapreoptic injection of prostaglandin E2

We previously reported that brain angiotensin II type 2 (AT2) receptors contribute to the hyperthermia induced by intrahypothalamic (intrapreoptic (i.p.o.)) administration of prostaglandin E2 (PGE2) in rats. The present study was carried out to investigate the role of angiotensin II (ANG II) receptors in the cardiovascular and adrenocorticotropic hormone (ACTH) responses induced in rats by i.p.o. injection of PGE2. PGE2 (100 ng) produced marked increases in blood pressure, heart rate, and plasma ACTH concentration. These changes were significantly enhanced by i.p.o. treatment with an AT1-receptor antagonist, losartan, while an AT2-receptor antagonist, CGP 42112A, had no effect. In contrast, losartan, but not CGP 42112A, reduced the pressor and ACTH responses to i.p.o. injection of a large dose of "exogenous" ANG II (25 ng). These results suggest that while "endogenous" ANG II exerts inhibitory effects on both the cardiovascular and the ACTH responses to i.p.o. PGE2 by way of preoptic AT1-receptors, a large dose of exogenous ANG II produces effects opposite to those induced by the endogenous ANG II that is released locally and in small amounts by i.p.o. PGE2.

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

Mechanisms of antiinflammatory action of the neuroimmunomodulatory peptide alpha-MSH

The antiinflammatory effects of alpha-melanocyte-stimulating hormone (alpha-MSH) molecules, specifically alpha-MSH(1-13) and its COOH-terminal tripeptide alpha-MSH(11-13), are well established. The peptides have been effective in tests of all major models of inflammation, and more recent tests have been extended to include experimental inflammatory bowel disease, CNS ischemia/reperfusion injury, and bacterial endotoxin-induced inflammation within the brain. The broad effectiveness of alpha-MSH molecules in all major types of inflammation indicates that the peptides exert actions that are very basic to the inflammatory process. Three general mechanisms of antiinflammatory action of alpha-MSH molecules have been identified: inhibition of production of inflammatory mediators by, or inhibition of inflammatory actions of, peripheral host cells; inhibition of peripheral inflammation induced by actions on melanocortin receptors within the brain; inhibition of CNS inflammation by local action of the peptides. It appears that alpha-MSH molecules have multiple actions that modulate the primitive inflammatory response.

Fatty acids and brain peptides

The role of fatty acids (FA) as a mediator and modulator of central nervous system activity in general, and peptides in particular, is only recently becoming understood. This paper reviews numerous findings concerned with the activity of fatty acids, particularly with their interaction with diverse neurochemical systems and their consequences for better understanding neurotransmitters, hormones and peptides. The effects include FA as precursors in the manufacture of neurochemical elements, including enzymes, neurotransmitters, and hormones. Of particular interest is the important changes in neuronal membrane composition that have been attributed to FA. Such changes may account for the changes in thermoregulation, learning, and other functions that accompany dietary manipulation of FA intake. While the total level of FA has been the object of many investigations, this report addresses the need to focus on the ratio of FA, especially alpha-linolenic/linoleic acid, which has been shown to be a critical factor in a number of research studies.

Blunted cortisol response after administration of corticotropin releasing hormone in endotoxemic dogs

To evaluate the effects of a standard inflammatory challenge on the dynamics of the hypothalamic-pituitary-adrenal (HPA) axis, we studied the effects of low-dose endotoxin (1.0 microgram/kg) on plasma adrenocorticotropic hormone (ACTH) and cortisol concentrations in a saline-controlled study in five awake dogs. Four hours after endotoxin or saline challenge human corticotrophin-releasing hormone (hCRH; 1.0 microgram/kg) was administered. Plasma ACTH and cortisol levels increased considerably in response to endotoxin, from 13 +/- 1 ng/l to 360 +/- 85 ng/l (p < 0.01) and from 60 +/- 20 nmol/l to 710 +/- 80 nmol/l (p < 0.01). Despite a considerable difference in ACTH and cortisol levels prior to CRH administration between both studies (p < 0.01), the absolute increase in ACTH levels induced by hCRH was not different (231 +/ 43 ng/l vs 238 +/- 45 ng/l, control vs endotoxin). Plasma cortisol levels increased significantly in the control study (from 40 +/- 10 nmol/l to 330 +/- 40 nmol/l, p < 0.01), whereas they did not change in the endotoxin study after hCRH administration (from 710 +/- 80 nmol/l to 730 +/- 70 nmol/l, ns). We conclude that the HPA-axis reacts initially to endotoxin in such a way that cortisol, but not ACTH, secretion is maximized. Therefore, a blunted cortisol response to CRH testing is part of the initial response to infection.

Hypothalamic prostaglandin E2 during lipopolysaccharide-induced fever in guinea pigs

Prostaglandin E2 (PGE2) is postulated to be a central mediator of fever. It is generally believed that it is produced in the preoptic area of the anterior hypothalamus (POA) because, among other evidence, its level increases both in the third ventricle and in the POA in response to pyrogens. However, lately, the question has arisen whether PGE2 might, in fact, be formed outside of the brain substance and then penetrate it, in particular through the organum vasculosum laminae terminalis. If produced outside the brain substance, the peripheral blockade of its synthesis should prevent lipopolysaccharides (LPS)-induced fever, whereas the intracarotid infusion of PGE2 should produce an increase in core temperature (T(C)) as well as in preoptic PGE2. To verify this hypothesis, continuous measurements of T(C) and preoptic PGE2 levels were made in conscious guinea pigs administered the PGE2 synthase inhibitor, indomethacin (10 or 50 mg/kg, im) 30 min before S. enteritidis LPS (2 mu g/kg, iv) or before PGE2 microdialyzed into the POA (1 mu g/mu l at 2 mu g/min for 2.5 h) and during PGE2 infused into a carotid artery (1 mu g and 10 mu g/mu l at 2 mu g/min for 1 h). LPS induced a biphasic 1.4 degrees C fever that was consistently associated with an increase in the level of PGE2 in the POA. Indomethacin at 10 mg/kg attenuated the course of the LPS-induced fever and prevented the associated increase in preoptic PGE2 for 90 min after fever onset; thereafter, PGE2 was significantly reduced by comparison with controls. Indomethacin at 50 mg/kg completely abolished both the fever and the increased levels of PGE2 in the POA; the fever induced by PGE2 microdialyzed into the POA was not affected by indomethacin pretreatment The intracarotid infusion of PGE2 produced T(C) falls and no increase in preoptic PGE2 levels. The indomethacin-induced blockade of fever and inhibition of the associated increase in preoptic PGE2 levels further substantiates the presumptive link between PGE2 in the POA and fever caused by LPS. The failure of exogenous PGE2 infusion to induce increases in T(C) and preoptic PGE2 levels excludes the possibility that PGE2 formed outside of the brain penetrates the POA and induces fever. Thus, in guinea pigs, the PGE2 associated with LPS-induced fever may be synthesized in the POA.