Regulation of bronchomotor tone in conscious calves

The purpose of this study was to investigate the effects of some a and β sympathomimetic and sympatholytic drugs on respiratory impedance in healthy conscious calves. Ten Friesian calves were investigated in this study. The forced oscillation technique was used to measure the resistance ( R _rs) and the reactance ( X _rs) of the respiratory system at frequencies ranging from 4 to 26 Hz. Isoprenaline (1 μg/kg i.v.), propranolol (3 μg/kg i.v.), noradrenaline (2 μg/kg i.v.), xylazine (20 μg/kg i.v.) and yohimbine (0.25 mg/kg i.v.) were administered. Isoprenaline induced a significant decrease of R _rs. An increase of R _rs after administration of propranolol was observed but without any change of the frequency dependence of R _rs. A small increase in the resonant frequency was also recorded. A decrease of R _rs was recorded after yohimbine injection. Noradrenaline and xylazine administration increased the resistances and the resonant frequency and induced a negative frequency dependence of R _rs. These results suggest that (1) the major effects of β adrenergic drugs are on the central airways, (2) the a adrenergic system may play a role on the regulation of bronchomotor tone in calves, (3) the effects of a adrenergic drugs are on both central and peripheral airways and (4) the forced oscillation technique allows the differentiation of calibre changes occurring in small and large airways.     

Effects of bovine respiratory syncytial virus on airway function in neonatal calves

Respiratory syncytial virus (RSV) infection causes severe lower respiratory tract disease in infants and calves. Neonatal respiratory tract infection in children often produces persistent changes in lung function. The specific objective of this study was to determine whether neonatal calves have transient or persistent alterations in pulmonary function and airway reactivity following RSV infection. Six 2- to 3-day-old Holstein bull calves were inoculated with 10 ml of bovine respiratory syncytial virus (BRSV) inoculum (10(2.7) to 10(3.8) cell culture infective doses/ml) intranasally and 10 ml of BRSV inoculum (10(4.8) to 10(5.9) cell culture infective doses/ml) intratracheally for 4 consecutive days, and 5 other calves were sham-inoculated. Prior to inoculation (day 0) and on days 4, 14, and 30 after the last inoculation, body weight (kg), dynamic compliance (Cdyn), pulmonary resistance (RL), and 2 indices of airway reactivity (effective dose [ED] 65Cdyn and ED200RL) were measured. Control calves gained weight progressively throughout the study, whereas RSV-inoculated calves failed to gain weight for 14 days, but equaled control calf weight by 30 days after inoculation. The Cdyn of control calves increased significantly by 30 days, but did not in the RSV-infected calves. Pulmonary resistance was increased significantly at 4, 14, and 30 days, but was unaffected by sham inoculation. The ED65Cdyn and ED200RL indicated an age-dependent increase in reactivity to histamine and an increase in responsiveness in the infected group beginning at 14 days and persisting until the end of the study.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of the monofrequency forced oscillation technique to measure changes in upper airway resistance in Friesian and blue Belgian calves

Monofrequency forced oscillometry ( ) using a sinusoidal test signal of one frequency (10 Hz) was compared with the classical pulmonary function technique (using an oesophageal balloon with airflow measurements) in two breeds of cattle which differ in their respiratory physiology, particularly to assess changes in upper airway resistance. Six healthy male Friesian calves (mean [ ] bodyweight 131 [12] kg) and six healthy male blue Belgian calves (mean [ ] bodyweight 137 [13] kg) were examined successively with their heads either in a normal position or held vertically, using a cross-over study design. In the normal position, higher resistances, a higher respiratory impedance, and lower values of the dynamic lung compliance (Cdyn) were measured in the blue Belgian than in the Friesian calves. In the vertical head position, total pulmonary resistance (RL) increased and Cdyn decreased significantly (P<0·05). The changes in -derived parameters were in accordance with the changes in classical parameters, and for both methods, the percentage changes were markedly higher in the blue Belgian calves.     

High performance liquid chromatography and pharmacokinetics of the non-steroidal anti-inflammatory drug oxindanac in calves

A high-performance liquid chromatographic method for the determination of the non-steroidal anti-inflammatory drug, oxindanac, in calf plasma is described. Recoveries over the concentration range 0.3 75 to 62.5 μg/ml were 90.2–107.8% with interassay coefficients of variation of 2.1–22.3%. The limit of detection was estimated as 0.10 μg/ml and the limit of quantification calculated to be 0.24 pg/ml in a 1 ml plasma sample. This method was used to establish the pharmacokinetics following intravenous (i.v.), intramuscular (i.m.) and oral (p.o.) administration to calves of oxindanac at a dose rate of 2 mg/kg. The elimination t ¹/₂, was long ( t 1/2 21.2 h after i.v. injection) and absorption was rapid (t¹/_2B 0.072 h) and complete ( F > 100%) following i.m. administration. Bioavailability was incomplete ( F = 66.6%) following p.o. administration to calves that had been fed on milk, and Wagner-Nelson analysis revealed twoabsorption phases ( t ¹/₂'s 0.20 and 1.9 h). Oxindanac produced long-lasting inhibition of serum TxB₂ production, with mean k_max values (% inhibition) of 96.8, 94.1 and 81.3 following i.v., i.m. and p.0. administration, respectively. A single i.v. or i.m. injection of 2 mg/kg oxindanac will probably be active in calves for at least 36–48 h.     

Disposition and bioavailability of neomycin in Holstein calves

Pedersoli, W.M., Ravis, W.R., Jackson, J., Shaikh, B. Disposition and bioavailability of neomycin in Holstein calves. J. vet. Pharmacol. Therap. 17 , 5–11.
The disposition and absorption kinetics of neomycin were studied in healthy ruminating dairy calves ( n -6), approximately 3-months-old. The calves were treated with single intravenous (i.v.) (12 mg/kg), intramuscular (i.m.) (24mg/kg), oral (p.o.) (96 mg/kg) and repeated p.o. (96 mg/kg, b.i.d., 15½ days) doses of neomycin. A 3-week rest period was allowed between treatments A and B and B and C Baseline and serial venous blood samples were collected from each calf plasma concentrations of neomycin were determined by a high performance liquid chromatography procedure. The resulting data were evaluated by using compartmental pharmacokinetic models and nonlinear least squares regression analysis. The mean of some selected parameters were t ½λ3 7.48 ± 2.02 h, Cl_t= 0.25 ± 0.04 L/h/kg, V _d(ss)= 1.17 ± 0.23 L/kg, and MRT = 4.63 ± 0.87 h for the i.v. data and t _½= 11.5 ± 3.8 h, MRT _abs= 0.960 ± 1.001 h, F = 127 ± 35.2%, and Cl_t/F = 0.199 ± 0.047 L/h/kg for the i.m. data, respectively. Only one calf absorbed neomycin to any significant degree (F = 0.0042) after a single p.o. dose. Selected mean parameters determined after repeated oral dosing were: F = 0.45 ± 0.45%, C_max= 0.26 ± 0.37 g/ml, and t_max= 2.6 ± 2.9 h. Terminal half-lives determined for the i.v. and i.m. treatments were considerably longer than those reported previously in the literature.     

Effect of endotoxin on tirilazad mesylate (U74006F) pharmacokinetic parameters in neonatal calves

Rose, M.L., Semrad, S.D., Putnam, M.L., Brown, S.A. Effect of endotoxin on tirilazad mesylate (U74006F) pharmacokinetic parameters in neonatal calves.J. vet. Pharmacol. Therap. 16, 438–445.
The pharmacokinetics of the 21-aminosteroid tirilazad mesylate (U74006F) were studied in both healthy and endotoxin-challenged neonatal calves. Group I calves received a 3-h intravenous (i.v.) infusion of sterile saline (250 ml) and tirilazad mesylate (1.5 mg/kg i.v.) 1 h after the start of the saline infusion. Group II calves received tirilazad mesylate 1 h after the start of a 3-h endotoxin (3.25 g/kg) infusion. The data obtained indicate that tirilazad mesylate follows a biexponential equation in neonatal calves. The area-derived volume of distribution (V_darea) was 9.68 ± 0.759 1/kg in healthy calves and 6.53 ± 1.20 1/kg in endotoxin-challenged calves ( P < 0.05). Similarly, significant (P <0.05) decreases in steady-state volume of distribution (Vj_ss) and central volume (VJ were observed in endotoxin-challenged calves (5.32 ± 0.979 1/kg and 1.68 ± 0.189 1/kg, respectively) compared to healthy calves (7.58 ± 0.834 1/kg and 2.43 ± 0.452 1/kg, respectively). A and B were significantly larger in endotoxin-challenged calves than in healthy calves ( P < 0.05). Rate constants and their associated half-lives, area under the curve and clearance were not significantly altered by endotoxin challenge. Serum thromboxane generation (ex vivo) was evaluated as a marker of the drug's physiologic activity. There was no significant difference in thromboxane generation during clotting of blood from healthy and endotoxemic calves treated with tirilazad mesylate.     

Pulmonary Eosinophilia Associated with Increased Airway Responsiveness in Young Racing Horses

Horses are known to acquire small airway disease (SAD), an allergen-induced naturally occurring syndrome of reversible obstructive lung disease accompanied by airway hyperresponsiveness and increased inflammatory cell numbers on bronchoalveolar lavage (BAL). This disorder has received scant attention in young racehorses. The purpose of the present report was to examine the effect of BAL eosinophilia in young racehorses on clinical examination, BAL, hematology, airway responsiveness, and on pulmonary function at rest and after a standardized exercise challenge. Five (3 males, 2 females; age 2.6 ± 0.9 years) with a history of respiratory compromise and BAL eosinophil differential count <5% and 6 controls (4 males, 2 females; age 3.5 ± 1.0 years) training and performing to expectation with normal BAL cell differential (eosinophils < 1%) were studied. Respiratory system clinical examination was performed and expressed as a clinical score. Arterial blood gas measurements, CBC, and pulmonary function testing were performed at rest. Pulmonary mechanics measurements were repeated 1 hour and 20 hours after a standardized treadmill exercise challenge. Incremental histamine inhalation challenge was performed and the concentration of histamine effecting a 35% decrease in dynamic compliance (PC35C_Dyn) was determined. Significant differences were noted between and controls with regard to clinical score ( P = .01), blood eosinophils ( P = .04), BAL cell count ( P = .04), BAL macrophage differential ( P = .04), PC35C_Dyn ( P = .008), and tidal volume and respiratory rate at 20 hours following exercise challenge ( P = .05). We conclude that pulmonary eosinophilia and airway hyperresponsiveness are manifest in some young horses without overt airway obstruction at rest. We speculate that these may be early events in the natural progression of heaves.     

Measurement of total respiratory impedance in dogs by the forced oscillation technique

The resistance (R _rs) and reactance (X _rs) of the total respiratory system were determined at various frequencies in 14 healthy conscious beagle dogs. A pseudorandom noise pressure wave was produced at the nostrils of the animals by means of a loudspeaker adapted to the nose by a tightly fitting mask. A Fourier analysis of the pressure and flow signals yielded meanR _rs andX _rs, over 16 s, at frequencies from 2 to 26 Hz. The influence of the posture of the dog, the position of its head, the linearity of the respiratory system, the reproducibility of the method and the effects of upper and lower airway obstructions were studied. In sitting and standing healthy dogs with the head in the extended position,R _rs values increased progressively with frequency from 5.4±0.4 (SEM) cmH₂O L^–1 s at 6 Hz up to 8.8±0.7 cmH₂O L^–1 s at 26 Hz, the mean resonant frequency being 6.1±0.5 Hz. No significant differences were observed between measurements performed with the head in the normal or the extended position. In a recumbent posture, allR _rs values were increased butR _rs was still dependent on the frequency in the same way (7.1±0.7 cmH₂O L^–1 s at 6Hz up to 10.0±0.5 cmH₂O L^–1 s at 26 Hz). Tracheal compression also induced higherR _rs values without changes in the frequency dependence or in the resonant frequency.In anaesthetized dogs, airway obstruction was induced by inhalation of histamine (4 mg/ml for 5 min; theR _rs values tended to decrease with increasing frequency, and the resonant frequency was markedly increased.Abbreviations FOT forced oscillation technique - IV intravenous(ly)     

Effects of aerosolized histamine and carbachol in the conscious horse.

Pulmonary function tests were performed in seven conscious, standing horses. Changes in pulmonary mechanics and ventilation volumes were measured after inhalation challenge with saline (baseline), histamine (1% w/v solution for 5 min) and carbachol (0.5% w/v solution for 3 min). Comparisons between baseline and posthistamine values revealed a significant (P less than 0.05) increase in nonelastic work of breathing (Wb), maximum change in transpulmonary pressure (max delta Ppl), and pulmonary resistance (RL), while dynamic compliance (Cdyn) decreased (P less than 0.05). Tripelennamine completely abolished these histamine induced changes suggesting the involvement of H1 receptors. A nonsignificant increase occurred in functional residual capacity. However, the amount of nitrogen retained in the lung at the end of a nitrogen washout test was significantly (P less than 0.05) greater after histamine when compared to baseline values. The effect of carbachol was qualitatively similar to that of histamine, Wb and max delta Ppl increased while Cdyn decreased (P less than 0.05). The increase in lower RL reached statistical significance (P less than 0.05) only at the beginning of expiration (/ 25% VT). The present investigation demonstrates that the physiological measurements of lung function could be carried out in conscious, unsedated horses and that the pulmonary function test methods could be used as a tool for study of drug induced changes in pulmonary mechanics.     

Effects of age and indomethacin on response and sensitivity of pulmonary artery to phenylephrine and to histamine in pigs

The vasoconstrictor effects of phenylephrine and histamine were investigated in isolated strips of pulmonary arteries in pigs during ageing. Interactions between phenylephrine-induced responses and arachidonic acid derivatives were also studied by incubating the blood-vessels with indomethacin. Potency (pD2 values) and maximal effects (E_maxx) recorded in 5-week-old piglets (group I, n = 5) with phenylephrine [5.71 ± 0.17 and 0.76 ± 0.22 g/mg of dry tissue respectively (mean ± SEM)] were similar to values found in 12-week-old animals (group 2, n = 5) (5.49 ± 0.30 and 1.06 ± 0.27 g/mg of dry tissue respectively). The sensitivity and responsiveness of tissues to this agonist were significantly reduced in 26-week-old mature pigs (group 3, n = 6) as indicated by the decrease in pD2 (3.91 ± 0.23; P < 0.01) and E_max (0.27 ± 0.13 g/mg of dry tissue; P < 0.05) values observed in this group. Histamine (10^_3M)-induced maximal responses (E_max) were significantly higher in group 2 (2.23 ± 0.49 g/mg) than in group 1 (0.85 ± 0.11 g/mg; P < 0.05) and in group 3 (0.48 ± 0.10 g/mg; P < 0.01). In 5-week-old animals, indomethacin (3.10˜⁵M) significantly ( P < 0.05) shifted the concentration-response curve to phenylephrine to the right (0.28 log. units) and depressed contractions to this drug as shown by the significant decrease of 39.5% ( P < 0.05) in E_max. This cyclo-oxygenase inhibitor had no effect in other groups. These data indicate that phenylephrine is a potent and effective vasoconstrictor agent for the main pulmonary arteries in 5-week-old piglets and that alpha-1-adrenergic-induced contractions are enhanced by cyclo-oxygenase products. These findings can be related with the high reactivity of pulmonary vascular smooth muscles in these animals.     

Correlation between the pharmacokinetics of oxindanac and inhibition of serum thromboxane B2 in calves

The pharmacokinetics and pharmacodynamics of the non-steroidal antiinflammatory drug, oxindanac, were assessed simultaneously in calves after intravenous (i.v.) administration at dose rates of 0.5, 1, 2, 4 and 8 mg/kg. Plasma pharmacokinetic data were fitted to either two or three compartment open models. The elimination t ¹/₂ was constant in the dose range 0.5 to 4 mg/kg (20.2–22.8 h) and shorter at 8 mg/kg (14.7 h). The pharmacodynamics of oxindanac were assessed by its inhibition of serum TxB₂, an index of platelet cyclo-oxygenase activity. Plots of total plasma oxindanac concentration vs. inhibition of serum TxB₂ fitted in all cases a sigmoidal E_max equation. There were no significant differences in the estimates for ED ₅₀ (1.6-1.9 μg/ml), Hill constant (1.3-2.7) or Emax between the doses used in the in vivo studies or when blood was spiked with oxindanac in vitro. Plots of inhibition of serum TxB₂ vs. time were prepared from the pharmacokinetic model equations in each calf in combination with a single sigmoidal E_max plot generated in vitro. These data were not significantly different from the results produced in vivo. It is concluded that oxindanac causes reversible inhibition of platelet cyclo-oxygenase in calves. Its inhibition of serum TxB₂ can be predicted from total plasma drug concentration, as described by a multicompartmental model, and sigmoidal E_max enzyme kinetics. It was not necessary to take into account factors such as drug equilibration between plasma and its target site, free vs. total drug concentration or chirality. This simple model may be useful for predicting the pharmacodynamics of oxindanac in other species.     

Monofrequency forced oscillation technique for the investigation of pulmonary function in calves: in vitro and in vivo studies

Parameters derived from the non-invasive and simple monofrequency forced oscillation technique were compared with classical parameters of ventilatory mechanics in order to assess its usefulness for the investigation of pulmonary function in calves. To facilitate this comparison, theoretical derivations were coupled with in vitro measurements, using an artificial lung model, and with in vivo studies. These studies compared the oscillatory resistance parameters (R_os and Re) and the respiratory system compliance (C_rs) against the classical pulmonary resistance (R_L) and the dynamic compliance (C_dyn), respectively. Ros and Re were highly correlated (r0·87) with R_L and the comparison between Crs and C_dyn gave a similarly high correlation (r0·88). Given its simplicity, its correspondence with classical parameters and its rapidity and reproducibility, monofrequency forced oscillation technique seems well suited for the investigation of pulmonary function under field conditions.     

Validation of the monofrequency forced oscillation technique for pulmonary function investigation in calves: an in vitro and in vivo study.

This study was to investigate whether the monofrequency forced oscillation (MFO) technique could be accurately used for pulmonary function testing in calves. The airflow resistance measured by this technique was compared to the resistance measured by the classical reference method by an in vitro study, using an artificial lung model, and by an in vivo study, using 11 healthy calves. The effect of the reference impedance of this oscillation equipment was also investigated. The results show linear relationships (r2 > 0.924, P < 0.001) in the resistance ranges 0 to 0.7 kPa litre-1 s and 0 to 1.0 kPa litre-1 s with a reference impedance of 1.0 kPa litre-1 s and 2.0 kPa litre-1 s, respectively. The MFO resistance values lower and higher than 0.4 kPa litre-1 s are slightly overestimated and underestimated, respectively. It was shown that, if some technical requirements are met, the MFO technique is a simple, reproducible, fast and accurate method which allows measurement of airflow resistance even in field conditions.     

Pharmacokinetics of enrofloxacin in newborn and one-week-old calves

The pharmacokinetic behaviour of enrofloxacin was compared in four one-day-old and four one-week-old calves in order to find out if there were any age-related differences. Mean volume of distribution ( V _d(ss)) and clearance ( Cl ) were significantly smaller in newborn calves: V _d(ss) was 1.8 and 2.3 L/kg, while clearance was 0.19 and 0.39 L/kg.h in newborn and one-week-old calves, respectively. Mean elimination half-life ( t _1/2β) did not differ significantly in newborn and in one-week-old calves: mean t _1/2β was 6.6 h and 4.9 h, respectively. Enrofloxacin was metabolized to ciprofloxacin both by newborn and one-week-old calves, but the maximum concentration ( C _max) of ciprofloxacin was lower and the time when maximum concentration was reached ( t _max) later in newborn calves. We conclude that the dosage of enrofloxacin should be adjusted according to age when administered to very young calves.     

A comparison of the various routes of administration of erythromycin in cattle

A comparison of i.v., i.m. and s.c. administration erythromycin base in polyethylene glycol at 15 mg/kg and 30 mg/kg body weight was carried out in beef-type calves of approximately 200 kg body weight. Additional evaluations were carried out with oral administration of erythromycin phosphate and erythromycin stearate. Absorption of erythromycin was very slow by both the i.m. and s.c. routes of administration with a K_ab of 0.0135 min^-1 and 0.0185 min^-1 for i.m. and 0.0032 min^-1 and 0.0074 min^-1 for s.c. at 15 mg/kg and 30 mg/kg, respectively. The bioavailability (32–42%) and peak serum concentrations were much lower with s.c. than with i.m. (60–65%) administration. The disposition of erythromycin administered i.v. appeared to be representative of dose-dependent kinetics rather than dose-independent first-order kinetics inasmuch as the elimination half-time ( t _1/2B) increased from 174.5 ± 13 min for the 15 mg/kg dosage to 239 ± 10.8 min with 30 mg/kg dosage. An acute apparent cardiovascular effect accompanied i.v. administration of erythromycin at 30 mg/kg dosage but not at 15 mg/kg. Severe diarrhea followed oral administration of either erythromycin phosphate or erythromycin stearate.     

The Effect of Edema, Hydrocortisone Acetate, Concurrent Viral Infection and Immunization on the Clearance of Pasteurella hemolytica from the Bovine Lung

The influence of pulmonary edema, hydrocortisone, immunization against Pasteurella hemolytica and concurrent infection with parainfluenza-3 virus upon pulmonary clearance of aerosolized P. hemolytica was studied in 31 calves. Following the various treatments calves were challenged with an aerosol of P. hemolytica. One control calf was killed immediately after the aerosol and the numbers of bacteria in the lung taken as 100%. Two calves were killed four hours after challenge and the numbers of bacteria in the lungs were compared to the 100% of the control calf. The result was the percentage clearance of bacteria at four hours.

Pulmonary edema was induced by three different methods: by an aerosol of histamine, by intravenous injection of endotoxin and by intravenous injection of croton oil emulsion. The edema impaired the clearance of P. hemolytica, which was reflected in high numbers of P. hemolytica present in the lungs at four hours after challenge: 260% after histamine, 300% and 400% after endotoxin and 92% after croton oil.

Six days of treatment of four calves with high doses of hydrocortisone acetate produced inconsistent results: two calves treated with a higher daily dose (36 mg/kg) had normal clearance whereas two calves treated with a lower dose had pulmonary edema and displayed lowered clearance with 111% and 31% respectively of P. hemolytica retained in the lungs four hours after challenge.

Immunization of calves by three different methods, a subcutaneously injected bacterin of P. hemolytica (2 calves), single aerosol (2 calves) and four aerosols (4 calves) of live P. hemolytica was reflected in an accelerated pulmonary clearance of P. hemolytica (with a mean of 1.55% of bacteria retained at four hours).

Concurrent infection with parainfluenza-3 virus did not lower the clearance of P. hemolytica in the lungs of 12 calves over 15 days except on the first day following the exposure to parainfluenza-3 virus. These calves had hemagglutinating antibodies against P. hemolytica before exposure.

     

Pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin after intravenous and oral administration of enrofloxacin in dogs

Rung, K., Riond, J.-L. & Wanner, M. Pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin after intravenous and oral administration of enrofloxacin in dogs. J. vet
Four dogs were given 5 mg/kg body weight enrofloxacin intravenously (i.v.) and orally (p.o.) in a cross-over study. Plasma concentrations of the active ingredient enrofloxacin and its main metabolite ciprofloxacin were determined by a reversed phase liquid chromatographic method. Pharmacokinetic parameters of both substances were calculated by use of statistical moments and were compared to those of enrofloxacin described in the veterinary literature. Mean enrofloxacin t _½λZ was 2.4 h, mean Cl_s was 27.1 ml/min-kg, and mean V_ss was 7.0 1/kg. After i.v. and p.o. administration, concentrations of ciprofloxacin exceeding minimal inhibitory concentrations of several microorganisms were reached (C_max= 0.2 ng/ml, max = 2.2 h after intravenous administration; C_max= 0.2 (ig/ml, t _max= 3.6 h after oral administration). A considerable part of the antimicrobial activity is due to ciprofloxacin, the main metabolite of enrofloxacin.     

Evaluation of a Whole Blood Glutaraldehyde Coagulation Test for the Detection of Failure of Passive Transfer in Calves

The accuracy of a commercially available whole blood glutaraldehyde clot test in the detection of failure of passive transfer (serum immunoglobulin [Ig]G₁ < 1,000 mg/dL) in neonatal calves was evaluated. Serum samples were obtained from 242 calves ranging in age from 1 to 8 days, and comparisons were made with serum lgG₁ concentrations determined by radial immunodiffusion. Both the sensitivity and specificity of the currently marketed whole blood glutaraldehyde clot test are inadequate for routine diagnostic use. Concerns regarding test sensitivity are the most problematic. Sensitivity varied from 0.41 to 0.00, depending on the choice of test endpoint. Specificity varied from 0.85 to 1.00, depending on the choice of test endpoint. Regression analysis demonstrated that the relationship between serum lgG₁ concentration and the glutaraldehyde clot results, although significant (P< .10), was of negligible biological relevance ( r ² = .034). J Vet Intern Med 1996; 10:82–84. Copyright © 1996 by the American College of Veterinary Internal Medicine .     

The effect of xylazine on plasma thromboxane B2 concentration in sheep

α₂-adrenoceptor agonist drugs can cause respiratory changes leading to a short period of hypoxaemia in sheep. It has been suggested that this is due to transient platelet aggregation and pulmonary microembolism. If platelet aggregation were to follow platelet activation in response to the administration of α₂ agonists, plasma thromboxane levels would be expected to rise. This study was carried out to measure plasma thromboxane B₂ concentrations before and after the intravenous administration of the α₂-agonist drug xylazine at a dose of 0.1 mg/kg. It was found that the plasma thromboxane concentration rose by 320% and, furthermore, the rise was prevented by the prior administration of atipamezole hydrochloride (0.125 mg/kg), an α₂-adrenoceptor antagonist.     

Determination of the ED50 of Isoflurane and Evaluation of the Isoflurane-Sparing Effect of Butorphanol in Cockatoos (Cacatua spp.)

The use of butorphanol as an analgesic in a psittacine species was evaluated by determining its isoflurane-sparing effects. The Effective Dose 50 (ED50) of isoflurane was determined using a bracketing technique based on the purposeful movement elicited by pressure applied to a digit with a hemostat. The ED50 of isoflurane for 11 cockatoos (four greater sulfur crested, three lesser sulfur crested, and four citron crested) was determined to be 1.44 ± 0.07%. After the administration of 1 mg/kg of butorphanol tartrate intramuscularly (IM), the ED50 was significantly ( P < .05) decreased to 1.08 ± 0.05%. Physiological variables that changed significantly included decreases in heart rate, tidal volume (V_t), inspiratory (T_j) and expiratory times (T_e), and an increase in respiratory rate. No complications resulted because of these changes. Based on the results, butorphanol produces an isoflurane-sparing effect in cockatoos and has the potential to be a useful analgesic in psittacines.