In vivo and in vitro metabolism of dexamethasone in the camel

The metabolism of dexamethasone (DXM) in the camel was assessed by in vivo and in vitro techniques. Liver samples were collected at the abattoir from camels of either sex, and microsomes were isolated and characterized as to their protein and haemoprotein content as well as for their ability to metabolise several cytochrome P450 model substrates. The expression of different P450 enzymes was evaluated by means of immunoblotting, and the glucuronidating capacity was assessed with 1-naphthol as the substrate. The activity of 11 beta-hydroxysteroid dehydrogenase type 1 was assayed using metyrapone as a model substrate. To examine the in vitro metabolism of DXM, microsomes were incubated with the corticoid in the presence of either a NADPH-generating system or of uridindiphosphoglucuronic acid. In vivo metabolism of DXM was studied in two male camels, injected with a bolus intravenous dose of DXM (0.2 mg/kg body weight) and DXM metabolites were evaluated in urine samples collected at different times after the administration. DXM and metabolites were extracted using solid phase and liquid-liquid extraction, and analysed by liquid chromatography mass spectrometry (LC/MS) and by LC/MS/MS. Comparative results were obtained by in vitro and in vivo studies. Two phase I metabolites were detected: the major one resulted from reduction of the 3-carbonyl group in ring A and the minor metabolite from ring hydroxylation of ring A. Glucuronidation involved both phase I metabolites as well as the parent compound.     

Sepsis and bacterial suppurative meningitis-meningoencephalitis in critically ill neonatal Piedmontese calves: clinical approach and laboratory findings

Sepsis (S) and bacterial suppurative meningitis-meningoencephalitis (M-ME) are common causes of death in bovine neonates. The aim of this prospective study was to evaluate the prevalence of S and M-ME in critically ill neonatal Piedmontese calves. Critically ill animals up to 15 days old referred by practitioners were registered according to their status and subsequently assigned to clinical standardized score. Calves with a clinical score > = 5 were further assessed under a clinical and clinical-pathological protocol to strengthen the suspicion of S and M-ME. Critically ill neonatal calves sent for necropsy were included in the study as well. Fifty-nine calves were investigated, 26 of which referred alive and 33 dead. Ten out of the 26 clinically evaluated calves were classified as suspicious of S on the basis of the clinical and clinical-pathological protocols. S was confirmed by positive bacteriologic culture in 7 cases and in 3 cases on the basis of necroptic lesions. Concomitant suppurative M-ME suspected in 6 of these 10 calves was subsequently confirmed by CSF analysis or histological findings. Of the 33 calves examined only post-mortem, 20 showed pathognomonic findings of S and 14 signs of M-ME. The prevalence of S and M-ME was 46 and 36 %, respectively. Clinical signs of S were confirmed to be vague and overlapping with other diseases. The developed protocol was highly accurate in predicting S in these neonatal calves.     

Comparative expression of liver cytochrome P450-dependent monooxygenases in the horse and in other agricultural and laboratory species

The apoprotein expression and the catalytic activities of cytochrome P450s involved in the biotransformation of xenobiotics were investigated in horse liver microsomes and compared with those of food producing (cattle, pigs, broiler chicks, and rabbits) and laboratory species (rats). Western blot analysis revealed the presence of proteins immunorelated to rat CYP 1A, CYP 2B, CYP 2E, and CYP 3A subfamilies in hepatic microsomes from horses and from any other examined species. With the exception of the N-demethylation of N-nitrosodimethylamine in broiler chicks, all the recorded interspecies differences were quantitative in nature. Equine preparations proved the most active in the biotransformation of the CYP 1A substrates ethoxy- and methoxyresorufin and the least active in the metabolism of aminopyrine and ethoxycoumarin. On a comparative basis, large differences were observed in the rate of the in vitro metabolism of model substrates between "minor" (rabbits, horses) and "major" food producing species. Taken in due consideration the limitations of the in vitro approach, results from this study reinforce the conclusion that studies on drug efficacy and residue depletion should be performed in each target species.     

Biotransformation enzymes as determinants of xenobiotic toxicity in domestic animals

After coming in contact with living organisms, the majority of foreign compounds undergo a number of chemical reactions known as biotransformations. These are performed by hepatic and extra-hepatic enzyme systems and usually yield more polar derivatives, referred to as 'metabolites', which may leave the body via the urinary and biliary routes or be excreted in animal products such as milk and eggs. Biotransformation does not always imply detoxification because in certain instances metabolites will be produced that are capable of reacting with tissue macromolecules or acquiring toxic properties different to or greater than those of the parent molecule.In this review, which is focused on domestic animals, the role played by oxidative, reductive, hydrolytic and conjugative biotransformation enzymes in the activation/detoxification of xenobiotics is examined. The relationship between extra-hepatic metabolism and target organ toxicity as well as the action of rumen microflora on feed additives, phytotoxins, and pesticides are then discussed. Some of the most important metabolic-based species-related susceptibilities to different poisons, and the influence of enzyme inducers or inhibitors on xenobiotic toxicity and drug safety are also reviewed.     

Potentiation of thein vitro activity of some antimicrobial agents against selected Gram-negative bacteria by EDTA-tromethamine

Thein vitro synergistic effects of combinations of EDTA-tromethamine and six antimicrobial agents (ampicillin, chloramphenicol, oxytetracycline, streptomycin, nalidixic acid and sulphadimethoxine) on clinically isolated strains ofPseudomonas aeruginosa, Proteus mirabilis andEscherichia coli were investigated. The antibacterial activity was assessed from the minimal inhibitory concentration for the antibiotics alone or in combination with EDTA-tromethamine. EDTA-tromethamine potentiated the antibacterial activity of ampicillin, chloramphenicol, oxytetracycline and streptomycin up to four-fold. There were no significant or consistent synergistic effects with nalidixic acid or sulphadimethoxine.Abbreviations cfu colony-forming units - EDTA ethylenediaminetetraacetic acid - MIC minimal inhibitory concentration - tromethamine tris(hydroxymethyl)aminomethane Part of this paper was communicated at the XLV Congress of the Italian Society of Veterinary Sciences, Palermo, 25–28 September 1991