Effects of chloramphenicol on infusion pharmacokinetics of propofol in greyhounds.

To investigate the effect of chloramphenicol, a cytochrome P-450 inhibitor, on the pharmacokinetics of propofol, either chloramphenicol (50 mg/kg of body weight, IV) or saline solution was administered IV to 5 Greyhounds in randomized manner, with at least 2 weeks between trials. Thirty minutes after either chloramphenicol or saline treatment, a bolus dose of propofol (10 mg/kg, IV) was administered, followed by a 2-hour infusion of propofol (0.4 mg/kg/min, IV). Samples for determination of blood propofol concentration were collected sequentially over a 6-hour period during each trial. After termination of propofol infusion, the time to spontaneous head lift, extubation, sternal recumbency, and standing was recorded. Blood propofol concentration was determined by use of high-performance liquid chromatography. Concentration-time data were fitted to a two-compartment open pharmacokinetic model and pharmacokinetic variables were determined, using a microcomputer program for modeling and simulation of concentration-time data. The effect of chloramphenicol on the pharmacokinetics of propofol and recovery time were evaluated, using paired t-tests and Wilcoxon's test for parameters that are not normally distributed (t1/2(beta), Vd(ss), ClB). Significant (P < 0.05) effects of chloramphenicol pretreatment included increased t1/2(beta) (by 209%), and decreased ClB (by 45%), and prolonged recovery indices (by 768 to 946%). These results indicate that cytochrome P-450 metabolic pathways have an important role in propofol clearance and propofol anesthetic recovery in Greyhounds.

Pasteurella haemolytica leukotoxin-induced synthesis of eicosanoids by bovine neutrophils in vitro.

Exposure of isolated bovine neutrophils to partially purified Pasteurella haemolytica leukotoxin caused increased synthesis of leukotriene B4 (LTB4) but not thromboxane B2 (TXB2) from endogenous arachidonic acid. Synthesis of LTB4 was closely correlated with leukotoxin-induced neutrophil lysis. At low toxin concentrations, LTB4 production lagged behind leukotoxin-induced neutrophil lysis over a 3-h period. The neutralizing monoclonal antileukotoxin antibody MM601 neutralized both leukotoxin-induced neutrophil lysis and LTB4 synthesis. Both leukotoxin-induced neutrophil lysis and LTB4 synthesis were Ca(2+)-dependent. When leukotoxin-induced LTB4 synthesis from exogenous arachidonic acid was examined, significant LTB4 synthesis occurred at 5 min of leukotoxin exposure, which was before leukotoxin-induced lysis developed. Leukotoxin-induced LTB4 synthesis from endogenous arachidonic acid appears to require leukotoxin-induced plasma membrane damage (occurring during neutrophil lysis), whereas LTB4 synthesis from exogenous arachidonic acid is initiated rapidly and occurs in the absence of plasma membrane damage.

Effects of localized Pasteurella haemolytica infection on erythromycin-binding properties of bovine alpha-1-acid glycoprotein, albumin, serum, and tissue chamber fluids.

The in vitro erythromycin-binding properties of bovine alpha-1-acid glycoprotein (AAG) and albumin were studied by using equilibrium dialysis. In addition, the proportions of free erythromycin in bovine serum and tissue chamber fluid before and 4 days after inoculation of subcutaneous tissue chambers with Pasteurella haemolytica were measured. At a concentration of 5 micrograms/ml, erythromycin was moderately bound to AAG (39% +/- 4% free) and was only slightly bound to albumin (86% +/- 2% free). Scatchard analysis of the data describing binding to pure bovine AAG indicated that erythromycin was bound to a single high-affinity (6.45 x 10(4) M-1) site on the protein. At lower total concentrations of erythromycin, the free concentrations of the antibiotic were lower in serum samples collected after infection (49% +/- 3% at 5 micrograms of erythromycin per ml) than in those collected before inoculation (55% +/- 3% at 5 micrograms of erythromycin per ml). Inoculation had no effect on binding to macromolecules in chamber fluids. Inoculated tissue chambers served as a convenient model for studying the effect of infection on drug-macromolecule interactions in interstitial fluid.

Metabolism of ethanol to 1-hydroxyethyl radicals in rat liver microsomes: comparative studies with three spin trapping agents.

Metabolism of ethanol to 1-hydroxyethyl radicals by rat liver microsomes was studied with three nitrone spin trapping agents (POBN, PBN, and DMPO) under essentially comparable conditions. The data indicate that POBN was the superior spin trapping agent for 1-hydroxyethyl radicals, and that DMPO was least efficient. Addition of deferoxamine completely prevented detection of 1-hydroxyethyl radicals with PBN or DMPO, but caused only 50% decrease in EPR signals when POBN was the spin trap. However, superoxide dismutase only decreased 1-hydroxyethyl radical formation when POBN was the spin trap. Other experiments demonstrated that POBN was the most effective of these nitrones for reduction of Fe(III) in aqueous solutions. Furthermore, 1-hydroxyethyl radical adducts were formed when POBN was added to mixtures of ethanol, phosphate buffer, POBN and FeCl3, but this effect did not occur with either PBN or DMPO. Thus, these data indicate that undesirable effects of POBN on iron chemistry may influence results of spin trapping experiments, and complicate interpretation of the resulting data.

Effect of Pasteurella haemolytica infection on alpha 1-acid glycoprotein and albumin concentrations in serum and subcutaneous tissue chamber fluid of calves.

Thermoplastic tissue chambers were implanted subcutaneously in the paralumbar fossae of 10 calves. Concentrations of alpha 1-acid glycoprotein (AAG) and albumin in serum and subcutaneous tissue chamber fluid were measured before and after inoculation of Pasteurella haemolytica into tissue chambers. Two months after implantation, serum and tissue chamber fluid samples were collected and all tissue chambers were then inoculated with P haemolytica. Additional serum and chamber fluid samples were collected two, four, six and 10 days after inoculation. The concentrations of AAG and albumin in the samples were measured by radial immunodiffusion assay and the bromcresol method, respectively. P haemolytica inoculation resulted in an increase in the serum and chamber fluid AAG concentrations and an increase in chamber fluid albumin concentrations, suggesting that the proportion of drugs bound to serum and interstitial proteins may be affected by P haemolytica infection.

Properties of engineered antifreeze peptides.

Eight antifreeze-like peptides were produced by cleavage from engineered chimeric proteins. One was homologous to an antifreeze peptide of the winter flounder; the others differed in length and/or sequence. The homologous peptide and all those of equal or greater length were able to inhibit recrystallization. The longer peptides were so hydrophobic that their identification required modification of the usual protocols for high pressure liquid chromatography. Their elution positions were correlated to their hydrophobicities and their lengths. Additional naturally occurring antifreezes may be identifiable with this knowledge.