A comparison of the effects of carbon dioxide and medical air for abdominal insufflation on respiratory parameters in xylazine-sedated sheep undergoing laparoscopic artificial insemination.

AIMS: To determine if abdominal insufflation with medical air will improve oxygenation and ventilation parameters when compared to insufflation with CO2 in xylazine-sedated sheep undergoing laparoscopic artificial insemination (AI). METHODS: Forty-seven sheep underwent oestrus synchronisation and were fasted for 24 hours prior to laparoscopic AI. Each animal was randomised to receive either CO2 or medical air for abdominal insufflation. An auricular arterial catheter was placed and utilised for serial blood sampling. Respiratory rates (RR) and arterial blood samples were collected at baseline, after xylazine (0.1 mg/kg I/V) sedation, 2 minutes after Trendelenburg positioning, 5 minutes after abdominal insufflation, and 10 minutes after being returned to a standing position. Blood samples were collected in heparinised syringes, stored on ice, and analysed for arterial pH, partial pressure of arterial O2 (PaO2), and CO2 (PaCO2). The number of ewes conceiving to AI was also determined. RESULTS: Repeated measures ANOVA demonstrated temporal effects on RR, PaO2, PaCO2 and arterial pH during the laparoscopic AI procedure (p<0.001), but no difference between insufflation groups (p>0.01). No sheep experienced hypercapnia (PaCO2>50 mmHg) or acidaemia (pH<7.35). Hypoxaemia (PaO2<70 mmHg) was diagnosed during the procedure in 14/22 (64%) ewes in the CO2 group compared with 8/23 (35%) ewes in the medical air group (p=0.053). Overall, 15/20 (75%) ewes in the CO2 group conceived to AI compared with 16/22 (72.7%) in the medical air group (p=0.867). CONCLUSIONS AND CLINICAL RELEVANCE: There were no statistical or clinical differences in RR, PaO2, PaCO2, pH, or conception to AI when comparing the effects of CO2 and medical air as abdominal insufflation gases. None of the sheep experienced hypercapnia or acidaemic, yet 42% (19/45) of sheep developed clinical hypoxaemia, with a higher percentage of ewes in the CO2 group developing hypoxaemia than in the medical air group. Based on the overall analysis, medical air could be utilised as a comparable alternative for abdominal insufflation during laparoscopic AI procedures.

Evidence for propofol hydroxylation by cytochrome P4502B11 in canine liver microsomes: breed and gender differences.

1. The study aimed to ascertain the enzyme kinetic basis for breed differences in the biotransformation of propofol in dog and to identify the responsible canine cytochrome P450 (CYP) isoenzymes. 2. The NADPH-dependent formation of 4-hydroxypropofol (the rate-limiting biotransformation in dog) was assayed using hepatic microsomes from the male greyhound and beagle, and from both sexes in mixed-breed dogs (five of each). 3. Enzyme kinetic analysis revealed that whereas there were no significant differences in Km, Vmax averaged > 3-fold lower in greyhound compared with beagle (p = 0.032). Although average Vmax was > 3-fold higher in the male compared with female mixed-breed dogs, this difference did not achieve statistical significance (p = 0.095), probably because of the high variability of data from mixed-breed dogs. 4. Chloramphenicol (a specific CYP2B11 inhibitor) and diethyldithiocarbamate (a non-specific CYP2 inhibitor) inhibited propofol hydroxylation in all microsomes. Quinine (a CYP2D15 inhibitor) was also inhibitory, but only in one-half of the microsomes examined. Immuno-inhibition by anti-CYP2B1 sera resulted in > 50% reduction in metabolite formation in all dogs except mixed-breed females, which showed a 30% reduction. Differences in propofol hydroxylase activity between microsomal preparations were primarily attributed to a component that was sensitive to inhibition by chloramphenicol and anti-CYP2B1 sera. 5. The results indicate that propofol hydroxylation in dog is primarily mediated by CYP2B11 and that breed (and possibly gender) differences in propofol metabolism may result from differences in the liver content of this CYP.

Propofol hydroxylation by dog liver microsomes: assay development and dog breed differences.

Pharmacokinetic studies indicate that clearance of propofol, an anesthetic agent, is slower in greyhounds compared with other dog breeds. Biotransformation of propofol to 2,6-diisopropyl-1,4-quinol (4-hydroxypropofol) by cytochrome P-450 in the liver is proposed as a critical initial step in the elimination of this drug in dogs. Breed differences in the activity of this enzyme could therefore explain pharmacokinetic differences. An in vitro propofol hydroxylase assay was developed and then used to compare enzyme activities in liver microsomes from male greyhound, beagle, and mixed-breed dogs (five each). HPLC of incubate identified only one NADPH-dependent metabolite, which had a chromatographic retention time and UV absorbance, fluorescence, and mass spectra that were identical with authentic 4-hydroxypropofol standard. HPLC with fluorescence detection provided a highly sensitive quantitation method for 4-hydroxypropofol with a quantitation limit of 8 ng/ml using optimized excitation/emission wavelengths (288 nm/330 nm, respectively). Estimates of apparent K(m) and V(max) for propofol hydroxylation by microsomes from a male beagle dog were 7.3 microM and 3.8 nmol/mg/min, respectively. At a substrate concentration of 20 microM, propofol hydroxylase activity was significantly lower (p =.032) in greyhound microsomes (1.7 +/- 0.4 nmol/mg/min) compared with beagle microsomes (5.1 +/- 1.3 nmol/mg/min) but was not statistically different (p =.42) compared with mixed-breed microsomes (3.1 +/- 1.2 nmol/mg/min). These results indicate that there are breed differences in propofol hydroxylase activity and that deficient hydroxylation of propofol by one or more hepatic cytochrome P-450 isoforms may contribute to slow pharmacokinetic clearance of propofol by greyhounds.

Vascular supply of the tendon of the equine deep digital flexor muscle within the digital sheath.

The vascular and microvascular anatomy of the equine deep digital flexor tendon (DDFT) within the digital sheath was studied by injecting the vasculature with either colored latex or barium sulphate for radiographic, microangiographic, histologic, and computed tomographic (CT) evaluation. Consecutive 4-mm thick two-dimensional CT slice data were reconstructed to 3-dimensional volumetric images to enhance spatial evaluation of the blood supply. Gross dissection and angiographic studies identified three major vascular sources. Above the fetlock, the DDFT was supplied by either a branch of the medial palmar artery (Arteriae digitalis palmaris communis II) or a branch of the medial palmar digital artery (A. digitalis [palmaris propria III] medialis). Below the fetlock, the DDFT was supplied by branches from the lateral and medial palmar branches to the proximal phalanx (Ramus palmaris phalangis proximalis). The most distal aspect of the tendon received small branches from the medial and lateral palmar digital arteries. Using histology and microangigraphy we observed an extensive and uniform intratendinous vascular network above and below the fetlock, with a relatively avascular region of tendon palmar to the fetlock. The most distal 2.0 to 2.5 cm of the tendon within the sheath was heavily infiltrated with fibrocartilage along its dorsal aspect.

Evidence for the Nuclear Location of the Genes for Chloroplast IF-2 and IF-3 in Euglena.

The chloroplast translational initiation factors IF-2 and IF-3 from Euglena gracilis are present in low levels in dark-grown cells and can be induced by exposure of cells to light. Studies of the antibiotic sensitivity of the light induction of these factors indicates that both are encoded in the nuclear genome.

Bovine mitochondrial ribosomes: effect of cations and heterologous dissociation factors on subunit interactions.

The effects of cations and ribosome dissociation factors on the equilibrium between the bovine mitochondrial ribosome and its subunits has been investigated. As observed with other ribosomes, Mg2+ ions promote subunit association while monovalent cations promote subunit dissociation. E. coli IF-3 will prevent the reassociation of mitochondrial 28 S and 39 S subunits. However, at least 5-fold higher concentrations of IF-3 are required with mitochondrial subunits than are required with bacterial subunits. The cytoplasmic factor eIF-6, has no detectable activity in preventing mitochondrial ribosomal subunit association.

Chloroplast initiation factor 3 from Euglena gracilis. Identification and initial characterization.

A chloroplast ribosome dissociation factor (IF-3chl) has been identified in whole cell extracts of Euglena gracilis. This work represents the first report of an organellar ribosome dissociation factor. E. gracilis IF-3chl facilitates the dissociation of Escherichia coli ribosomes as demonstrated by sucrose density gradient analysis. Chloroplast IF-3 stimulates initiation complex formation on E. coli ribosomes with natural mRNA from the bacteriophage MS2. In addition, IF-3chl is effective in initiation complex formation with Euglena chloroplast or E. coli ribosomes in the presence of synthetic mRNA. IF-3chl is induced 12-fold by exposure of the cells to light. The chloroplast factor has been purified 30-fold by chromatography on DEAE-cellulose and phosphocellulose. The chromatographic properties of this factor differ considerably from those of prokaryotic ribosome dissociation factors.

Stereochemical aspects of the metabolism of 5-ethyl-5-phenylhydantoin (Nirvanol) in the dog.

Enantiomers of 5-ethyl-5-phenylhydantoin (EPH) were administered to dogs, and urinary metabolites were quantitated. After administration of (R)-EPH, the urinary products included unchanged drug, 5-ethyl-5-(4-hydroxyphenyl)hydantoin (p-EHPH), 5-ethyl-5-(3-hydroxyphenyl)hydantoin (m-EHPH), and an N-glucuronide of EPH. Administration of (S)-EPH gave urinary products consisting of unchanged drug, p-EHPH, m-EHPH, an N-glucuronide of EPH, and a dihydrodiol metabolite, which has been isolated and identified as (5 S)-5-[(3R,4R)-3,4-dihydroxy-1,5-cyclohexadien-1-yl]-5-ethylhydantoin. The levorotatory isomers of p- and m-EHPH have been assigned the (R)-configuration. An unidentified metabolite of EPH has been detected through its reactivity under basic conditions to yield 2-ethyl-2-phenylhydantoic acid, which can be cyclized with acid to EPH. Quantitative studies of the disposition of single oral doses of (R)-, (S)-, and (RS)-EPH by these metabolic routes suggest that the metabolism of one enantiomer is unaffected by the presence of the other enantiomer. Stereoselectivities of metabolic pathways are discussed in relation to stereoselectivities observed for phenytoin metabolism in the dog.

Determination of 5-(3,4-Dihydroxy-1,5-cyclohexadien-1-yl)-5-phenylhydantoin (Dihydrodiol) and quantitative studies of phenytoin metabolism in man.

A routine gas chromatographic assay for urinary 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH), the major metabolite of phenytoin (PHT) in man, was adapted to allow quantitation of 5-(3,4-dihydroxy-1,5-cyclohexadien-1-yl)-5-phenylhydantoin (Dihydrodiol, DHD) is based on the observation that acid-catalyzed dehydration of DHD quantitatively yields a mixture of p-HPPH and m-HPPH in a reproducible molar ratio of 56:44p-HPPH: m-HPPH and on the assumption that all m-HPPH found in urine after heating with acid has been derived from DHD. The urinary DHD content was verified by a "specific" method in which urine was incubated with beta-glucuronidase and the released phenolic metabolites completely removed by extraction. Subsequent acid-catalyzed dehydration of the remaining DHD yielded p-HPPH and m-HPPH, from the sum of which the original DHD concentration in urine could be calculated. In all of the urine samples from PHT patients examined to date, there was close agreement between the DHD values obtained by the "specific" method and those calculated from m-HPPH, in the simple acid-hydrolysis method. It can be inferred that much the greater part (greater than 90%) of m-HPPH found in human urine after acid treatment has been derived from DHD. All samples of urine after acid treatment has been derived from DHD. All samples of urine from PHT patients examined have shown detectable quantities of DHD. The methods described here may be useful in a survey of PHT patients to reveal unusual patterns of PHT metabolism and to permit recognition of possible associations between such unusual patterns and the occurrence of adverse reactions.

Gas chromatographic on-column methylation technique for the simulataneous determination of antiepileptic drugs in blood.

An on-column methylation technique (OCMT) is described for the simultaneous, gas chromatographic determination in blood of ethosuximide (ES), phenobarbital (PB), primidone (PD), phenytoin (DPH), and 5-ethyl-5-phenylhydantoin (EPH). Multiple internal standards are employed in the OCMT, in order to eliminate or to minimize greatly error sources common to the technology of gas chromatography and to compensate for the different chemical dispositions of the antiepileptic drugs in an OCMT. The internal standards used in the OCMT were as follows: alpha,alpha,beta-trimethylsuccinimide (TMS) was used for the determination of ES; 5-ethyl-5-para-tolylbarbituric acid (MPB), for PB; 5-ethyl-5-(para-tolyl) hexahydropyrimidine-4,6-dione (MPD), for PD; and 5-(para-tolyl)-5-phenylhydantoin (MPPH), for EPH and DPH. The use of ether, the buffering of the plasma sample at pH 7.6, and the use of dilute (0.30-0.35 M) trimethyl-phenylammonium hydroxide (TMPAH) contributed to the specificity of the extraction scheme of the OCMT. The precision and accuracy of the OCMT was attributed to the use of appropriate, multiple internal standards. A method is described for the preparation of standard solutions of drugs in blank plasma (biological matrix) and for the use of the standards in calibration and daily intra-laboratory control of the OCMT.