A. S. J. P. A. M. Van Miert

Pathophysiological effects of endotoxins in ruminants. 1. Changes in body temperature and reticulo-rumen motility, and the effect of repeated administration.

Data from the literature on the clinical effects of bacterial endotoxins in ruminants are reviewed. Special attention is paid to the effects on body temperature and reticulo-rumen motility. Furthermore, the effects of repeated intravenous injection of endotoxin are summarised. Pathophysiological disturbances after intramammary infusion of endotoxins proved to be identical to those found after intravenous injection of non-lethal doses. Strikingly, however, no marked inhibitory effect on rumen motility nor abortion was observed after intramammary infusion of endotoxins. Moreover, in cows that were made tolerant to endotoxin by daily intravenous injections, intramammary infusion of one-fifth of this daily dose produced a maximum effect on body temperature and plasma Zn concentrations. This suggests that inflammatory endogenous mediators were released in the udder and then absorbed into the blood circulation, rather than the absorption of endotoxin.

Participation of β-adrenergic receptors on macrophages in modulation of LPS-induced cytokine release

For several years it is known that beta-adrenergic receptor agonists have anti-inflammatory effects. However, little is known about the role of beta-adrenergic receptors on macrophages in the modulation of cytokine production by beta-agonists during inflammation. In this study, the presence of beta-receptors on PMA-differentiated U937 human macrophages, and the participation of these receptors in the modulation of LPS-mediated cytokine production by beta-agonists was investigated. Total beta-receptor expression on undifferentiated (monocyte) and PMA-differentiated U937 cells was established using receptor binding studies on membrane fractions with a radio ligand. The expression of beta-receptors proved to be significantly lower on monocytes than on macrophages, additionally a predominant expression of beta 2-receptors was found. Production of the cytokines TNF-alpha, IL-6, and IL-10 by LPS-stimulated differentiated U937 cells was measured in time. Peak concentrations for TNF-alpha, IL-6 and IL-10 occurred at 3, 12 and 9 hrs, respectively. When differentiated U937 cells were incubated with both LPS and the beta-agonist clenbuterol the production of TNF-alpha and IL-6 was significantly reduced. However the production of IL-10 was increased. To study the mechanism of modulation of cytokine production in more detail, U937 macrophages were incubated with LPS/clenbuterol in combination with selective beta 1- and beta 2-antagonists. These results indicated that the beta 2- and not the beta 1-receptor is involved in the anti-inflammatory activity of clenbuterol.

Pro-inflammatory cytokines in a ruminant model: pathophysiological, pharmacological and therapeutic aspects

Summary Infection evokes complex changes which are thought to be caused by the production and release of pro‐inflammatory cytokines such as tumour necrosis factor (TNF‐α), interferons (IFNs), and interleukins (ILs). They regulate local inflammatory reactions, but may also gain access to the circulation and induce systemic effects collectively known as the Acute Phase Response. To improve our understanding of the pathophysiology of proinflammatory cytokines in ruminants, studies have been performed with TNF‐α, IL‐1α/β and IFN‐α/γ, as well as with cytokine‐inducers in dwarf goats. In relation to therapy, the following aspects may be of interest: a) Cytokine therapy given before or just after microbial challenge induces in vivo antimicrobial activity. Moreover, cytokines potentiate in vivo the antimicrobial activity of antibiotics, b) Cytokines may act as biological response modifiers for enhancing specific immunity to vaccines, and c) Cytokines may affect drug absorption, disposition, and metabolite formati...

Primary bovine hepatocytes in the study of cytokine induced acute-phase protein secretion in vitro

To investigate the utility of primary cultures of bovine hepatocytes for compartmentalized acute phase protein studies the secretion of serum amyloid-A (SAA) and haptoglobin (Hp) was measured after stimulation by pro-inflammatory cytokines (recombinant human IL-6 (rhIL-6) and recombinant human tumour necrosis factor-alpha (rhTNF-alpha)). During the incubation period of the experiment, the SAA and Hp secretion into the culture medium increased (P < 0.05). SAA concentrations showed an additional increase following treatment with each of the cytokines (P < 0.01). Hp concentrations remained unchanged, whereas incubation with a combination of both resulted in a significant increase of the medium concentration of both SAA (P < 0.01) and Hp (P < 0.05). From these findings it is concluded that primary bovine hepatocytes can be used for in vitro studies on acute-phase protein secretion.

Characterization of cytochrome P450 isoenzymes in primary cultures of pig hepatocytes

Despite the fact that pigs are increasingly used in pharmacological and toxicological studies, knowledge on the enzymes which metabolize xenobiotics, in particular cytochrome P450 (CYP) enzymes, in pigs is still very limited. Primary cultures of pig hepatocytes were used to characterize CYP enzymes. The characterization was performed at the level of enzymatic activities, apoprotein and mRNA analyses. Enzyme inducers investigated were beta-naphthoflavone (BNF), phenobarbital (PB), dexamethasone (DEX) and rifampicin (RIF). After 48hr of BNF treatment, CYP1A protein and mRNA levels were increased, and ethoxyresorufin O-deethylation and caffeine 3-demethylation were strongly induced. PB and RIF increased the levels of CYP3A apoprotein and mRNA, whereas BNF down-regulated CYP3A and related activities. PB and RIF treatment resulted in increased ethylmorphine N-demethylation and testosterone hydroxylation, which appears to be the result of CYP3A induction. Hybridization of pig RNA with a human CYP2C9 cDNA probe showed a PB and RIF inducible CYP, which was down-regulated by BNF. Similar inducing effects were observed for tolbutamide, a marker substrate for CYP2C. DEX was not a potent inducer, although some induction of CYP3A mRNA was observed. The present results indicate the absence of CYP2B and probably CYP2D enzymes and activities in pig liver. Despite some dissimilarities, the results indicate that pigs, apart from their very human-like physiology, might represent a more appropriate model species for oxidative drug metabolism in humans than rats.

Present concepts on the inflammatory modulators with special reference to cytokines.

The pro- and anti-inflammatory cytokines create a network of interactions between cells that lead to both stimulatory and inhibitory responses that maintain an effective homeostatic regulation. The anti-inflammatory cytokines are a family of peptides that modulate the pro-inflammatory cytokine response. Cytokines act in concert with non-cytokine mediators, such as prostaglandin E2, glucocorticosteroids, lipocortins, and catecholamines. This review highlights new developments in our understanding of the pathophysiology of inflammation and gives an example of a more recent approach to the modulation of acute systemic inflammatory disorders: activation of β2-adrenergic receptors on macrophages. In this respect the potent β2-adrenergic agonist clenbuterol seems of therapeutic interest.The pro- and anti-inflammatory cytokines create a network of interactions between cells that lead to both stimulatory and inhibitory responses that maintain an effective homeostatic regulation. The anti-inflammatory cytokines are a family of peptides that modulate the pro-inflammatory cytokine response. Cytokines act in concert with non-cytokine mediators, such as prostaglandin E2, glucocorticosteroids, lipocortins, and catecholamines. This review highlights new developments in our understanding of the pathophysiology of inflammation and gives an example of a more recent approach to the modulation of acute systemic inflammatory disorders: activation of β2-adrenergic receptors on macrophages. In this respect the potent β2-adrenergic agonist clenbuterol seems of therapeutic interest.

Fever and associated clinical haematologic and blood biochemical changes in the goat and other animal species.

Summary Acute febrile diseases are characterized by specific and non‐specific symptoms. The non‐specific responses are presented under the headings: fever, inflammation and pain, experimental models for investigating febrile reactions, haematologic changes, blood biochemical changes, cardiovascular effects, changes in gastric function, and the effects of fever upon pharmacokinetics of drugs. It was the purpose of this review to describe present concepts of thermoregulation and fever, the associated reactions produced by bacterial pyrogens and the mechanisms of these reactions. The available data illustrate, that many questions have not yet been clearly answered. However, the entire field of research involving endogenous substances, such as interleukin‐1, is now moving ahead with great speed. Furthermore, there is some evidence which suggests that fever and the associated lower plasma zinc and iron levels act together as a co‐ordinated non‐specific host defence mechanism. Since experimental fever has a dis...

Endotoxin-induced liver damage in rats is minimized by β2-adrenoceptor stimulation

AbstractObjective and Design: To investigate the effects of β2-adrenoceptor (β2-AR) stimulation on endotoxin-induced liver damage and systemic cytokine levels in rats. Subjects: Standard male Wistar rats. Treatment: A disease-model of lipolysaccharide (LPS)-induced acute systemic inflammation was used. The β2-selective AR agonist clenbuterol was administered before, during, and after LPS-challenge to investigate its effects on the acute inflammatory response and associated liver-failure. Methods: The following parameters have been measured in plasma: TNFα, IL-1β, IL-6, IL-10, AST, ALT, and Bilirubin. Liver histological examination was performed to look for changes in tissue morphology. Results: Administration of clenbuterol (p.o.) one hour before, or intravenous at the same time as LPS-challenge resulted in a marked reduction of plasma levels of TNFα, IL-1β, and IL-6. A change both in plasma-level and in time-concentration profile of the anti-inflammatory cytokine IL-10 was found. Clenbuterol minimized LPS-induced liver damage, as represented by significantly lowered concentrations of several parameters for liver-failure (AST, ALT, Bilirubin), and improved hepatic tissue morphology. Clenbuterol administration after LPS challenge failed to inhibit TNFα-release but reduced liver-damage. Simultaneous use of the β2-AR antagonist propranolol augmented LPS-induced liver failure, suggesting a role of endogenous adrenoceptor-agonists in prevention of organ-failure during systemic inflammation. Conclusions: The results indicate that a selective β2-AR agonist might be used as an additional therapeutic agent in the clinic for the treatment of (acute) systemic inflammatory disorders in order to reduce or prevent subsequent liver failure.

Selective effects of a bacterial infection (Actinobacillus pleuropneumoniae) on the hepatic clearances of caffeine, antipyrine, paracetamol, and indocyanine green in the pig

1. In order to investigate the effect of a bacterial acute phase response model on drug disposition in vivo, plasma clearances of antipyrine, caffeine, paracetamol and indocyanine green were investigated in the healthy and Actinobacillus pleuropneumoniae-infected pig. 2. Indocyanine green plasma and endogenous creatinine clearance were not changed during the infection, which indicates that hepatic blood flow and renal function were not significantly affected. 3. In the A. pleuropneumoniae-infected pig, plasma clearances of antipyrine and caffeine, both marker substrates for hepatic oxidative biotransformation, were decreased by 72 and 68% respectively. The clearance of paracetamol, a drug mainly glucuronidated in the pig, was reduced by 39%. 4. It is concluded that the most important change in drug elimination during an acute phase response induced by A. pleuropneumoniae is a suppression of oxidative hepatic biotransformation.

Fever and changes in plasma zinc and iron concentrations in the goat. The effects of interferon inducers and recombinant IFN-α2a

Inflammation or invasion by pathogenic micro-organisms induces systemic changes, collectively known as the acute phase response. Among the varied alterations that together produce this response are fever, hypoferraemia and hypozincaemia. It is likely that these responses are mediated, in part, by production and release of cytokines such as interleukin-1 (Il-1), interferons (IFN-alpha) and tumour necrosis factor (TNF). The present report describes a comparative study in dwarf goats on recombinant human IFN-alpha 2a (0.5 x 10(5) IU per kg intravenously (i.v.) and 0.5 x 10(6) IU per kg intramuscularly (i.m.], Poly I:Poly C (an interferon inducer; 30 micrograms per kg i.v.), Newcastle disease virus La Sota strain (an interferon inducer; 0.5 ml per kg i.v.) and Escherichia coli endotoxin (an Il-1 and TNF inducer; 0.1 microgram per kg i.v.). The i.v. injection of recombinant IFN-alpha 2a caused characteristic monophasic febrile reactions, but no significant changes in plasma zinc and iron concentrations. The temperature responses were not due to endotoxin contamination because polymyxin B, which blocks endotoxin, had no inhibitory effect on the pyrogenicity of IFN-alpha 2a. In contrast, the IFN-alpha 2a-induced fever was completely prevented by flurbiprofen pretreatment (1 mg per kg i.v.). In contrast to the i.v. administration, i.m. injection of IFN-alpha 2a caused fever, hypoferraemia and hypozincaemia. Similar results were obtained after E. coli endotoxin, NCD La Sota strain and Poly I:Poly C injection. However, the shapes of the temperature curves and the changes in trace metal concentrations were markedly different. These data support the theory that fever and the changes in plasma zinc and iron concentrations are regulated by different mechanisms.