Antigen-specific antibodies in cerebrospinal fluid after intramuscular injection of ovalbumin in horses

Eighteen normal horses were assigned to 1 of 3 treatment groups to investigate the effects of IM or intrathecal (IT) administration of ovalbumin on serum and cerebrospinal fluid (CSF) antibody production. Horses of group 1 were injected intramuscularly with ovalbumin and adjuvant, while horses in treatment groups 2 and 3 received ovalbumin intrathecally or intravenously, followed by IM injection as in group 1. Serum and CSF antibody titers were tested in group I every 30 days for 4 months, while serum and CSF were collected in group 2 and 3 horses at postvaccination day 60. Horses of group 1 (IM) developed a serum antibody titer that peaked at postadministration day 60 (1:24,320 +/- 7,680) (mean +/- I SEM). Anti-ovalbumin antibodies were detected in CSF, and titers paralleled that of the serum, although at a much lower concentration (peak, 1:166 +/- 87). Horses of groups 2 and 3 developed significantly (P = .02) lower serum titers (1:720 and 1:2,067, respectively), but the difference in CSF titers did not achieve statistical significance (P = .06). The results confirm that antigen-specific antibody can be found in the CSF of horses in which antigen is not administered intrathecally. This may affect the interpretation of CSF analysis in diseases such as equine protozoal myeloencephalitis. Further, the findings suggest that IT injection of the soluble antigen ovalbumin induces a state of antigenic tolerance in the horse. The clinical significance of this finding remains unknown at this time.     

Trans-endothelial and trans-epithelial transfer of lactoferrin into the brain through BBB and BCSFB in adult rats

The transportation of intravenously administered bovine lactoferrin (bLF) into the cerebrospinal fluid (CSF) was immunohistochemically investigated in adult rats. Administered bLF was detected in the vesicular membranes of endothelial cells in cerebral blood vessels 10 min after the infusion. Numerous immunoreactive small vesicles were also detected at the ependymal cells in the choroid plexus. Moreover, the bLF concentration in the CSF was significantly increased at 1-2 hr after the intravenous infusion of bLF (10 or 30 mg/kg). These findings clearly demonstrate that LF is possibly transported into the brain matter even in adult animals.     

Flow cytometric evaluation of multidrug resistance proteins on grossly normal canine nodal lymphocyte membranes

OBJECTIVE: To demonstrate efficacy of flow cytometric evaluation of expression and activity of P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) efflux pumps and characterize and correlate their expression and activity in grossly normal canine nodal lymphocytes. SAMPLE POPULATION: Nodal lymphocytes from 21 clinically normal dogs. PROCEDURES: Pump expression was assessed by use of fluorescent-labeled mouse antihuman P-gp (C494) and MRP1 (MRPm6) antibodies and expressed as median values (antibody value divided by isotype control value). The P-gp and MRP activities were assessed by measuring cellular retention of rhodamine 123 and 5(6)-carboxyfluorescein diacetate in the absence and presence of inhibitors (verapamil and PSC833 for P-gp, probenecid and MK-571 for MRP). Protein activity was expressed as median fluorescence of cells with inhibitors divided by that without inhibitors. RESULTS: Expression of P-gp was (mean +/- SEM) 50.62 +/- 13.39 (n = 21) and that of MRP was 2.16 +/- 0.25 (13). Functional activity was 1.27 +/- 0.06 (n = 21) for P-gp and both inhibitors and 21.85 +/- 4.09 (21) for MRP and both inhibitors. Function and expression were not correlated. CONCLUSIONS AND CLINICAL RELEVANCE: Use of flow cytometry effectively assessed P-gp and MRP expression and activity in canine lymphocytes. Optimization of the flow cytometric assay was determined for evaluating activity and expression of these pumps in canine lymphoid cells. Evaluation of expression or activity may offer more meaning when correlated with clinical outcome of dogs with lymphoproliferative diseases. Cell overexpression of P-gp and MRP can convey drug resistance.     

The relation between the birth process and the condition of the newborn piglet and calf

Fluxes of the anti-parasitic agents, [³H]-ivermectin, [³H]-selamectin and [³H]-moxidectin were studied across non-transfected and transfected canine kidney epithelial monolayers, MDCK II/wt, MDCK II-MDR1, MDCK II-MRP1 and MDCK II-MRP2. All four lines surprisingly expressed significant levels of P-glycoprotein (P-gp), coded for by MDR1, but MDCK II-MDR1 expressed increased levels compared to the other lines. MDCK II-MRP1 and MDCK II-MRP2 expressed increased levels of MRP1 and MRP2 respectively. Fluxes of [³H]-ivermectin, [³H]-selamectin, [³H]-moxidectin, and the P-gp substrates, rhodamine-123 and DiOC₂, were polarized in the basolateral-to-apical (secretory) direction across the four lines. Selected MRP inhibitors used in relevant pharmacological concentrations did not block the secretory fluxes of either [³H]-ivermectin or [³H]-selamectin in either the non-transfected or MRP-transfected lines. In contrast, secretory fluxes of ivermectin and selamectin were inhibited in all four lines by the P-gp inhibitor, verapamil. These data confirm that ivermectin and selamectin are substrates for P-gp in four additional cell lines, but suggest that they are not significant substrates for MRP1 or MRP2 where there is background expression of P-gp. Since this pattern of expression also pertains on the blood-brain barrier, it is unlikely that MRP1 and MRP2 play a significant role in ivermectin and selamectin blood: brain distribution in vivo.     

Use of albumin quotient and IgG index to differentiate blood- vs brain-derived proteins in the cerebrospinal fluid of cats with feline infectious peritonitis

BACKGROUND: Inflammation of the central nervous system (CNS) is a frequent condition in cats but etiology often remains unsolved. Routine cerebrospinal fluid (CSF) analysis can be extended through the calculation of the albumin quotient (Q(alb)), a marker of the integrity of the blood-brain barrier (BBB), and IgG index, an estimate of intrathecal IgG synthesis. OBJECTIVES: The purpose of this study was to validate nephelometric methods for CSF protein analysis, and to use the Q(alb) and IgG index to discriminate blood- and brain-derived immunoglobulin fractions in cats with feline infectious peritonitis (FIP). METHODS: Cats presented to our clinic between 2001 and 2005 were included in the study based on clinical and laboratory data and histopathologic findings at necropsy. Cats were grouped as having nonneurologic disease (controls; n=37), brain tumors (n=8), FIP involving the CNS (n=12), and extraneural FIP (n=12). CSF-total protein (TP) was measured and albumin and IgG concentrations were measured in paired CSF/serum samples; Q(alb) and IgG index were calculated. Intraassay and interassay precision of the nephelometric assays were determined using pooled samples. RESULTS: Coefficients of variation for the nephelometric assays ranged from 2.7% to 7.2%. In control cats, CSF-TP concentration ranged from 0.06 to 0.36 g/L, Q(alb) ranged from 0.6 to 5.7 x 10(-3), and IgG index ranged from 0.3 to 0.6. Q(alb) and IgG index were significantly higher in cats with brain tumors and cats with CNS-FIP compared with other groups. Compared with control cats, pleocytosis was evident in 8 of 12 (67%) cats and CSF-TP was increased in 3 of 12 (25%) cats with CNS-FIP. CONCLUSION: Nephelometry is a reliable method for measurement of CSF protein, albumin, and IgG in cats. The Q(alb) and IgG index did not identify a CSF protein pattern specific for BBB dysfunction or intrathecal IgG synthesis in cats with CNS-FIP.     

Expression of P-glycoprotein and breast cancer resistance protein in three cases of canine lymphoma showing drug resistance

In canine lymphoma, drug resistance is the major factor hindering treatment. In this study, we performed immunohistochemical examination of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), which are considered as transporters related to multidrug resistance in three recurrent canine lymphomas. All cases were negative for both transporters before anticancer drug administration, but became positive after this administration. The expression was confirmed in capillary endothelial cells, such as in brain capillaries acting as the blood-brain barrier (BBB). It is suggested that both transporters expressed on capillary endothelial cells in lymphoma tissue may inhibit the spread of anticancer drugs into tumor tissues from blood, the same as the BBB. Therefore, capillary endothelial cells could act as a blood-tumor barrier, which might be involved in drug resistance in canine lymphoma.     

The interaction between moxidectin and MDR transporters in primary cultures of rat hepatocytes

The interaction of moxidectin (a macrocyclic lactone, ML) with P-glycoprotein (P-gp), multidrug resistance associated proteins (MRPs) and breast cancer resistance protein (BCRP) was studied in primary cultures of rat hepatocytes by measuring the intracellular accumulation of [14C]-moxidectin over 72 h in the presence of specific inhibitors: for P-gp, verapamil (10 microM); for MRPs, MK571 (100 microM), indomethacin (10 microM) and probenecid (3.8 mM); and for BCRP, fumitremorgin C (5 microM). The P-gp and MRP inhibitors increased significantly (P < 0.01) by 48.7%, 49.8%, 49.9% and 57.2% the area under the time-intracellular concentration curve (AUC) of moxidectin in rat hepatocytes, while the BCRP inhibitor, fumitremorgin C, had no effect on the AUC compared with the control. In addition, the mRNAs of all the drug transporters studied were detected in rat hepatocytes from 0 to 72 h. Using this cellular model it has been shown that MRP inhibitors increase moxidectin intracellular concentrations to a similar extent as the P-gp inhibitor. The identification of all the transporters that interact with MLs remains a challenge, which currently concerns several important therapeutic fields.     

The ABCB1-1Δ mutation is not responsible for subchronic neurotoxicity seen in dogs of non-collie breeds following macrocyclic lactone treatment for generalized demodicosis

P-glycoprotein (P-gp), encoded by the multiple drug resistance gene ABCB1 (also known as MDR1 ), is an integral component of the blood brain barrier crucial in limiting drug uptake into the central nervous system. Altered expression or function of P-gp, as seen in dogs of the collie lineage homozygous for the nt228(del4) mutation of the ABCB1 gene ( ABCB1-1Δ ), can result in potentially fatal neurotoxicosis, especially following administration of systemic macrocyclic lactones (SML). Occasionally, dogs from unrelated breeds develop subchronic signs of neurotoxicity when receiving SML to treat generalized demodicosis. It is possible that these dogs are heterozygous carriers of the ABCB1-1Δ mutation, resulting in decreased P-gp activity and central neurotoxicosis. Cheek swabs were collected from 28 dogs with generalized demodicosis that had shown subchronic signs of neurotoxicity following daily oral administration of ivermectin or other SML. Ten of these animals received concurrent systemic treatment with other confirmed or putative P-gp substrates. After DNA extraction, the relevant portion of the ABCB1 gene was amplified by polymerase chain reaction, and sequenced. Twenty-seven dogs were homozygous normal while one dog was heterozygous for the ABCB1-1Δ mutation. Therefore, with the exception of one dog, the observed neurotoxicity could not be attributed to the ABCB1-1Δ mutation. Possible explanations for the adverse reactions observed include pharmacological interactions (administration of SML with other P-gp substrates or inhibitors), excessively high doses, polymorphisms in P-gp expression, uncharacterized mutations in the ABCB1 gene or in another gene, or phenomena unrelated to the SML–P-gp interaction.     

Blood–brain‐barrier disruption in chronic canine hypothyroidism

Background: Central nervous system (CNS) manifestations of hypothyroidism have been associated with cerebrovascular complications. Reports of cerebrospinal fluid (CSF) abnormalities are rare in hypothyroid dogs. Objective: The aim of this study was to determine if chronic hypothyroidism causes blood–brain‐barrier (BBB) abnormalities that are detectable using indirect CSF biomarkers. Methods: The study included 18 normal, euthyroid, female mixed‐breed dogs. Hypothyroidism was induced by ¹³¹iodine administration in 9 dogs; 9 served as untreated controls. Evaluations included physical and neurologic examination, complete CSF analysis, serum and CSF protein electrophoresis, measurement of plasma vascular endothelial growth factor (VEGF) and serum S‐100B concentrations, and calculation of CSF albumin quota (AQ) and were conducted at baseline and 6, 12, and 18 months after induction of hypothyroidism. Data were analyzed using repeated measures ANOVA. Results: At baseline, differences between groups were not detected for any variable. Throughout the study, controls dogs remained free of neurologic disease and had test variables that remained within reference intervals. Two hypothyroid dogs developed CNS signs during the study, and evidence of cerebrovascular disease was found at necropsy. At 12 and 18 months, the CSF total protein, VEGF, S‐100B, and fractional albumin concentrations, and AQ were significantly higher (P<.04) in hypothyroid dogs than controls. Among test variables assayed in serum or plasma, the only significant difference was a higher S‐100B concentration in hypothyroid dogs (P=.003) at 18 months. Conclusions: BBB integrity is disrupted in chronic hypothyroidism. Significant increases in CSF concentrations of VEGF and S100‐B in hypothyroid dogs indicate dysfunction in both endothelial and glial elements of the BBB.     

Some factors influencing the level of clinical sedation induced by medetomidine in rabbits

Rabbits (n=23) received intravenous bolus medetomidine at 100 mug/kg. Prior to medetomidine administration, heart and respiratory rates were measured, arterial blood was collected and analysed for plasma cortisol, glucose and albumin concentrations. Fifteen minutes after medetomidine administration, heart and respiratory rates were measured again and sedation was scored. The rabbit was afterwards anaesthetized with 20 mg/kg ketamine administered intravenously to enable spinal tap and heart puncture. Cerebrospinal fluid (CSF) was collected (this occurred 20 min post medetomidine administration) and analysed for medetomidine concentration. Blood was collected by heart puncture immediately after the spinal tap and analysed for serum medetomidine concentration. Cerebrospinal fluid medetomidine concentration correlated negatively with sedation. Serum medetomidine correlated positively with CSF medetomidine concentration. Cerebro-spinal fluid medetomidine was 17 +/- 13% of serum medetomidine concentration. Plasma cortisol and glucose concentrations correlated negatively with serum medetomidine. We conclude that after an intravenous bolus administration of a low sedative dose of medetomidine to rabbits; CSF concentration of the drug correlate negatively with sedation and that this may be because of the fact that only the free and unbound medetomidine may be available for detection in the CSF, the concentration of medetomidine detected in the CSF was much lower than that in blood and a positive correlation exists between CSF and serum medetomidine concentrations. Stress may have some effect on the distribution or metabolism of medetomidine in rabbits.     

Expression of cyclooxygenase-2, P-glycoprotein and multi-drug resistance-associated protein in canine transitional cell carcinoma

Cyclooxygenase-2 (COX-2), P-glycoprotein (P-gp) and multi-drug resistance-associated protein (MRP) are considered important tumor-associated proteins in humans and dogs. In the present study, we immunohistochemically evaluated the expression of these proteins in canine patients with transitional cell carcinoma (TCC). Of 52 cases, 30 (57.7%) were positive for COX-2, 40 (76.9%) for P-gp, and only 10 (19.2%) for MRP. In addition, 27 samples (27/52, 51.9%) were positive for two markers, while 3 (5.7%) and 5 (9.6%) cases were positive and negative, respectively, for all three markers. No significant correlations were seen for COX-2 and P-gp on Fisher's exact test and Mann-Whitney's test, but a significance was seen on Spearman's rank correlation analysis using the IHC scoring system (P=0.043). These results suggest that P-gp expression is induced by overexpression of COX-2 in canine patients with TCC.     

The effect of 7.2% hypertonic saline solution on the duration of sodium gradient between the cerebrospinal fluid and the venous circulation in the dog

To determine the duration of water movement from cerebrospinal fluid (CSF) into venous blood by the infusion of 7.2% hypertonic saline solution (HSS), the sodium gradient between venous blood and CSF were examined. Venous sodium concentrations remained higher than that in CSF for duration of 60 min following HSS infusion. By 90 min, the CSF sodium concentration reached the equilibrium with venous sodium concentration. Those data suggests that the duration of time during which water moved from CSF into capillaries in brain by the gradient of sodium concentration was less than 90 min.     

黄芩苷对大鼠口服非索非那定的药动学影响

为了研究黄芩苷在大鼠体内对非索非那定药动学及P-gp表达的影响,将SD大鼠36只随机分为A、B、C三组,连续灌胃7天,A组给予黄芩苷200mg/kg,B组蒸馏水空白对照,C组维拉帕米药物对照(10mg/kg),第8天灌胃后2小时,各组随机取6只大鼠处死,解剖并迅速取出肝脏、空肠,荧光定量PCR测定各组织P-gp的mRNA表达水平。各组另外6只大鼠灌胃后同时给予非索非那定（30mg/kg）,按时间点连续采集血样,采用高效液相色谱法测定非索非那定血药浓度。结果表明,黄芩苷对非索非那定的吸收有明显促进作用,主要表现在黄芩苷组非索非那定峰浓度(Cmax)比空白对照组增加17.04%（P<0.05）,曲线下面积AUC(0-12)增加19.23%（P<0.05）,黄芩苷减少了大鼠空肠和肝脏P-gp蛋白的表达（P<0.05）。结论：黄芩苷能下调大鼠P-gp表达,增加P-gp底物非索非那定在大鼠体内的生物利用度,是一种P-gp抑制剂。     

Effect of intravenous administration of dextrose or lactated Ringer's solution on seizure development in dogs after cervical myelography with metrizamide

The effect of fluid (5% dextrose in water or lactated Ringer's solution) administered intravenously on the development of seizures after cervical myelography with metrizamide was studied in 10 dogs. In a crossover experimental design, 8 dogs were used twice. Urine output was measured during the second part of the study to determine whether diuresis was a factor affecting seizure development. Dogs given 5% dextrose in water had significantly (P less than 0.05) fewer seizures than did dogs given lactated Ringer's solution. This was attributed to an increase in CSF glucose concentration and was not associated with diuresis.     

Intrauterine administration of plant oils inhibits luteolysis in the mare

Reasons for performing the study: The maternal recognition of pregnancy (MRP) signal in the mare has not been determined, although oestrogens have been proposed as a potential candidate. Objectives: To determine effects of intrauterine administration of oestrogen and various oils on cyclic luteolysis in the mare. Hypothesis: Intrauterine oestradiol or fatty acids may suppress luteolysis in the cycling mare when administered during late dioestrus. Methods: A single 1 ml dose of slow‐release oestradiol (10 mg/ml) in fractionated coconut oil was infused into the uterine lumen of cycling mares on Days 6, 8, 10, 12 or 14 post ovulation (n = 12 in each group). Four further groups, each of 12 mares, received an intrauterine infusion of either 1 ml of fractionated coconut oil, peanut oil, mineral oil or a slow‐release preparation of oestradiol (10 mg/ml) in mineral oil on Day 10 post ovulation. Serial blood samples were assayed for progesterone concentrations to monitor luteal function. Results: Intrauterine administration of oestradiol in fractionated coconut oil showed peak efficacy at Day 10 when luteolysis was delayed in 11/12 (92%) mares. The ability of the treatment to delay luteolysis was not significantly different when administered on Days 8 (9/12; 75%), 12 (10/12; 83%) or 14 (6/12; 50%) of dioestrus, but declined significantly when given on Day 6 (3/12; 25%). Oestradiol was not needed to initiate luteostasis since fractionated coconut oil alone or peanut oil administered at Day 10 induced the same high rate of luteal persistence (11/12; 92% for both oils). In contrast, mineral oil did not prolong luteal lifespan, either when administered alone (2/12; 17%) or combined with oestradiol (3/12; 25%). Conclusion: These results do not unequivocally rule out a possible involvement of embryonic oestrogens in MRP in the mare but suggest it is unlikely. The results demonstrate that plant oils can postpone luteolysis, suggesting they may modulate synthesis or release of prostaglandins from the mare's endometrium. Potential relevance: Administration of fractionated coconut or peanut oil on Day 10 post ovulation provides an effective and practical method of prolonging luteal function (‘pseudopregnancy’) thereby suppressing unwanted oestrous behaviour. Further studies to elucidate the mechanism by which this is achieved may increase understanding of both luteostasis and MRP signal in the mare.     

Effects of intravenous tryptophan infusion on thermoregulation in steers exposed to acute heat stress

This study was conducted to investigate the effect of tryptophan (TRP) supply on the thermoregulatory responses via brain serotonin (5‐HT) in cattle. In period 1, 12 Holstein steers were kept under a constant room temperature (22°C) and were administered the intravenous (i.v.) infusion of saline or TRP (38.5 mg/kg/2 h). Changes in rectal temperature (RT), 5‐HT concentration in the cerebrospinal fluid (CSF), and other factors involved in thermoregulation were measured. In period 2, the steers received the same treatments as in period 1; however, the room temperature was elevated from 22°C to 33°C during i.v. infusion and maintained at 33°C for 3 h. 5‐HT concentration in CSF increased following TRP infusion in both periods, and RT significantly decreased following TRP infusion only in period 2. The effect of TRP on respiration rate and plasma prolactin and total triiodothyronine concentrations was not significant. These results suggest that increase in TRP supply can attenuate increase in RT in response to acute heat stress through the increase in brain 5‐HT, followed by presumable increase in evaporative heat loss from the skin surface in cattle. It is possible that the increase in peripheral blood TRP metabolites could also participate in the hypothermic effect of TRP.     

Cardiorespiratory and endocrine effects of endogenous opioid antagonism by naloxone in ponies anaesthetised with halothane

Halothane depresses cardiorespiratory function and activates the pituitary-adrenal axis, increasing beta endorphin. In horses, beta endorphin may enhance the anaesthetic-associated cardiorespiratory depression and mortality risk. The authors studied endogenous opioid effects on cardiorespiratory function and pituitary-adrenal activity in halothane-anaesthetised ponies by investigating opioid antagonism by naloxone. Six ponies were anaesthetised three times (crossover design). Anaesthesia was induced with thiopentone and maintained with 1.2 per cent halothane for 2 hours. Immediately after induction, naloxone was administered either intravenously (0.5 mg kg(-1)bolus then 0.25 mg kg(-1)hour(-1)for 2 hours) or intrathecally (0.5 mg) or was replaced by saline as control. Pulse and respiratory rates, arterial blood gases, cardiac output and plasma cortisol and adrenocorticotrophic hormone (ACTH) concentrations were measured. All groups developed cardiorespiratory depression (40 per cent decrease in cardiac output) and plasma cortisol increased. Plasma ACTH concentration was higher in ponies treated with intrathecal naloxone. Endogenous opioids may inhibit ACTH secretion, attenuating the stress response to halothane anaesthesia in equidae.     

Involvement of P-glycoprotein on ivermectin kinetic behaviour in sheep: itraconazole-mediated changes on gastrointestinal disposition

Different pharmacological approaches have been used in an attempt to increase the systemic availability of anthelmintic drugs. The comparative effect of the itraconazole (ITZ)-mediated modulation of P-glycoprotein (P-gp) activity on the in vivo kinetic behaviour of ivermectin (IVM) administered by the intravenous (i.v.) and intraruminal (i.r.) routes to sheep was assessed in the current work. Corriedale sheep received IVM (50 microg/kg) by the i.v. route either alone (group A) or co-administered with the P-gp modulator ITZ (100 mg orally three times every 12 h) (group B). Animals in groups C and D were intraruminally treated with IVM (50 microg/kg) alone or co-administered with ITZ (100 mg orally three times every 12 h) respectively. Jugular blood and gastrointestinal tissue samples (animals treated by the i.r. route) were collected. The samples were analysed by HPLC using fluorescence detection. The plasma disposition of IVM given intravenously was unaffected by the presence of ITZ. However, after the i.r. treatment the co-administration with ITZ resulted in markedly higher IVM plasma concentration profiles compared to the control group. Likewise, the presence of ITZ enhanced the IVM concentration profiles measured in the gastrointestinal mucosal tissues. An ITZ-induced reduction on the P-gp efflux activity at the intestinal lining may have accounted for the greater absorption and enhanced systemic availability observed for IVM in the intraruminally treated animals.     

Concentrations of vatinoxan and xylazine in plasma,cerebrospinal fluid and brain tissue following intravenous administration in sheep

ObjectivesTo investigate the extent of vatinoxan distribution into sheep brain, and whether vatinoxan influences brain concentrations of xylazine; and to examine the utility of cerebrospinal fluid (CSF) as a surrogate of brain tissue concentrations for vatinoxan and xylazine.Study designRandomised, blinded, experimental study.AnimalsA total of 14 adult female sheep.MethodsSheep were randomly allocated into two equal groups and premedicated with either intravenous (IV) vatinoxan (750 μg kg^–1, VX) or saline (SX) administered 10 minutes before IV xylazine (500 μg kg^–1). Sedation was subjectively assessed at selected intervals before and after treatments. At 10 minutes after xylazine administration, a venous blood sample was collected and the sheep were immediately euthanised with IV pentobarbital (100 mg kg^–1). Plasma, CSF and brain tissues were harvested, and concentrations of vatinoxan and xylazine were quantified using liquid chromatography–tandem mass spectrometry. Drug ratios were then calculated and the data were analysed as appropriate.ResultsThe brain-to-plasma and CSF-to-plasma ratios of vatinoxan were 0.06 ± 0.013 and 0.05 ± 0.01 (mean ± standard deviation), respectively. Xylazine brain concentrations were not significantly different (835 ± 262 versus 1029 ± 297 ng g^–1 in groups VX and SX, respectively) and were approximately 15-fold higher than those in plasma. The CSF-to-brain ratio of vatinoxan was 0.8 ± 0.2, whereas xylazine concentrations in the brain were approximately 17-fold greater than those in CSF, with and without vatinoxan.Conclusions and clinical relevanceVatinoxan did not significantly affect sedation with xylazine or the concentrations of xylazine in the brain. CSF is not a good predictor of xylazine concentrations in the brain, whereas vatinoxan concentrations were concordant between the brain and CSF, using the dosages in this study.     

Serum and tissue concentrations of erythromycin in calves with induced pneumonic pasteurellosis

The effects of pneumonia on the pharmacokinetics of erythromycin administered IM and the tissue concentration changes with time were evaluated in 2-month-old calves. Pneumonia was induced by injection of Pasteurella haemolytica cultures through the thoracic wall into each lung. Six days prior to induction of pneumonia, erythromycin (15 mg/kg) was administered in a single IM dose. Erythromycin was administered again 48, 72, and 96 hours after injection of P haemolytica. On the third day of erythromycin administration (96 hours), the calves were serially euthanatized in groups of 4 calves each at 2, 5, 8, 12, 18, and 24 hours after the final dose was given. Tissue concentrations of erythromycin in kidney, liver, lung, muscle, CSF, and serum were determined. Neither the serum concentrations nor the overall pharmacokinetic values were significantly (P less than or equal to 0.05) changed by pneumonia. The concentrations of erythromycin were maximal at 5 hours for liver, muscle, and serum and at 8 hours for CSF, kidney, and lung. Serum and muscle concentrations were similar, whereas concentrations in CSF were lower than in serum and higher in kidney, liver, and lung. The lung/serum ratios were approximately 2.5 to 3 at 8 through 24 hours after IM administration. The peak concentration in lung was approximately 6 micrograms/g at 8 hours.