Thirty horses were randomly assigned to 1 of 5 groups. All horses were anesthetized and subjected to ventral midline celiotomy, then the large colon was exteriorized and instrumented. Colonic arterial blood flow was reduced to 20% of baseline (BL) and was maintained for 3 hours. Colonic blood flow was then restored, and the colon was reperfused for an additional 3 hours. One of 5 drug solutions was administered via the jugular vein 30 minutes prior to colonic reperfusion: group 1, 0.9% NaCl; group 2, dimethyl sulfoxide: 1 g/kg of body weight; group 3, allopurinol: 25 mg/kg; group 4, 21-aminosteroid U-74389G: 10 mg/kg; and group 5, manganese chloride (MnCl2): 10 mg/kg. Hemodynamic variables were monitored and recorded at 30-minutes intervals. Systemic arterial, systemic venous (SV), and colonic venous (CV) blood samples were collected for measurement of blood gas tensions, oximetry, lactate concentration, PCV, and plasma total protein concentration. The eicosanoids, 6-keto prostaglandin F1alpha, prostaglandin E2, and thromboxane B2, were measured in CV blood, and endotoxin was measured in CV and SV blood. Full-thickness biopsy specimens were harvested from the left ventral colon for histologic evaluation and determination of wet weight-to-dry weight ratios (WW:DW). Data were analyzed, using two-way ANOVA for repeated measures, and statistical significance was set at P < 0.05. Heart rate, mean arterial pressure, and cardiac output increased with MnCl2 infusion; heart rate and cardiac output remained increased throughout the study, but mean arterial pressure returned to BL values within 30 minutes after completion of MnCl2 infusion. Other drug-induced changes were not significant. There were significant increases in mean pulmonary artery and mean right atrial pressures at 2 and 2.5 hours in horses of all groups, but other changes across time or differences among groups were not observed. Mean pulmonary artery pressure remained increased through 6 hours in all groups, but mean right atrial pressure had returned to BL values at 3 hours. Mean colonic arterial pressure was significantly decreased at 30 minutes of ischemia and remained decreased through 6 hours; however, by 3.25 hours it was significantly higher than the value at 3 hours of ischemia. Colonic arterial resistance decreased during ischemia and remained decreased throughout reperfusion in all groups; there were no differences among groups for colonic arterial resistance. Colonic venous PO2, oxygen content, and pH decreased, and PCO2 and lactate concentration increased during ischemia but returned to BL values during reperfusion. Compared with BL values, colonic oxygen extraction ratio was increased from 0.5 to 3 hours. By 15 minutes of reperfusion, colonic oxygen extraction ratio had decreased from the BL value in all groups and either remained decreased or returned to values not different from BL through 6 hours. Colonic venous 6-keto prostaglandin F1alpha and prostaglandin E2 concentrations increased during ischemia, but returned to BL on reperfusion; there were no changes in thromboxane2 concentration among or within groups. Endotoxin was not detected in CV or SV blood after ischemia or reperfusion. There were no differences among or within groups for these variables. Low-flow ischemia and reperfusion (I-R) of the large colon caused mucosal injury, as evidenced by increases in percentage of surface mucosal disruption, percentage depth of mucosal loss, mucosal hemorrhage, mucosal edema, mucosal interstitial-to-crypt ratio, mucosal neutrophil index, submucosal venular neutrophil numbers, and mucosal cellular debris index. There was a trend (P = 0.06) toward greater percentage depth of mucosal loss at 6 hours in horses treated with dimethyl sulfoxide, compared with the vehicle control solution. There were no differences in the remainder of the histologic variables among groups. Full-thickness and mucosal WW:DW increased with colonic I-R, but there were no differences among groups. There was a trend (P = 0.09) toward neutrophil accumulation, as measured by myeloperoxidase activity, in the lungs after colonic I-R, but there were no differences among groups. There was no change in lung WW:DW after colonic I-R. There were no beneficial effects of drugs directed against oxygen-derived free radical-mediated damage on colonic mucosal injury associated with low-flow I-R. Deleterious drug-induced hemodynamic effects were not observed in this study.

Because caffeine is metabolized by the hepatic P-450 cytochrome oxidase system, clearance of caffeine is an excellent quantitative test of hepatic function in human beings. It is currently used in much the same way that creatinine clearance is used to assess renal function. Caffeine clearance was measured in lactating dairy cows initially to determine the suitability of caffeine clearance as an indicator of hepatic function in cattle. Pharmacokinetic variables of caffeine were studied in 6 adult lactating dairy cows after IV administration of a single dose of caffeine sodium benzoate (2 mg of caffeine/kg of body weight). Caffeine concentration was analyzed by use of an automated enzyme immunoassay. The lower limit of detection of the assay for caffeine in serum was 0.079 micrograms/ml. Serum caffeine concentration-time curves best fit an open two-compartment pharmacokinetic model. Harmonic mean elimination half-life was 3.8 (range, 2.6 to 6.9) hours, and total clearance was 0.118 (range, 0.090 to 0.197) L/kg/h. Milk caffeine concentration was similar to serum concentration 1.5 to 24 hours after caffeine administration. Adverse effects were not observed in cows given caffeine.

Twenty-four horses were randomly allocated to 3 groups. All horses underwent a ventral midline celiotomy, and the large colon was exteriorized and instrumented. Group-1 horses served as sham-operated controls, group-2 horses underwent 6 hours of colonic ischemia, and group-3 horses were subjected to 3 hours of ischemia and 3 hours of reperfusion. Baseline blood samples were collected, then low-flow colonic ischemia was induced in horses of groups 2 and 3 by reducing colonic arterial blood flow to 20% of baseline. All horses were monitored for 6 hours. Citrated systemic venous (SV) blood samples were collected from the main pulmonary artery, and colonic venous (CV) samples were collected from the colonic vein draining the ventral colon. Samples were collected at 0, and 2, 3, 3.25, 4, and 6 hours for determination of one-stage prothrombin time, activated partial thromboplastin time, antithrombin III activity, and fibrinogen concentration. Data were analyzed statistically, using two-way ANOVA for repeated measures, and post-hoc comparisons were made by use of Student Newman Keul's test. Statistical significance was set at P < 0.05. There were significant decreases in all hemostatic variables by 2 hours in SV and SV samples from horses of all 3 groups, but there were no differences among the 3 groups for any of these variables. These hemostatic alterations could have been secondary to a hypercoagulable state or to fluid therapy-induced hemodilution. Colonic ischemia-reperfusion was not the cause of these alterations because these alterations also were observed in the sham-operated control horses. Significant temporal alterations existed even after accounting for the hemodilution. The most plausible explanation for these alterations is that hemostatic activation was incited by the celiotomy and manipulation of the colon during exteriorization and instrumentation. Comparison of paired SV and CV samples for each hemostatic variable revealed significant differences for the absolute values of one-stage prothrombin time and fibrinogen concentration, but not for activated partial thromboplastin time or antithrombin III activity. This indicates that monitoring SV hemostatic variables does not necessarily provide an accurate assessment of hemostatic function in regional vascular beds. Large-colon ischemia with or without reperfusion did not alter hemostatic function.

Receptors for opsonins, such as complement component C3b (CR1) and immunoglobulins, Fc receptors, interact with adhesion glycoproteins in mediating immune functions. Defects in expression of the adhesion glycoproteins CD11/CD18 results in severely hampered in vitro and in vivo adherence-related functions of leukocytes. Little is known regarding the effect of leukocyte adhesion deficiency (LAD) on ligand binding and receptor expression. We investigated the binding and expression of CR1 and Fc receptors by bovine neutrophils isolated from dairy calves suffering from LAD, compared with clinically normal (hereafter referred to as normal) age-matched calves. Neutrophils were also assayed for endogenously bound IgG and IgM and for exogenous binding of C3b, IgG1, IgG2, IgM, and aggregated IgG (aIgG), using flow cytometry. Luminol-enhanced chemiluminescence (CL) production in response to IgG2 opsonized zymosan was studied, and specific inhibition of CL was used to determine the specificity of IgG2 binding. Activation of protein kinase C with phorbol myristate acetate was used to determine the effect of cellular activation on expression of CR1. A greater percentage of neutrophils from normal calves bound C3b than did neutrophils from LAD-affected calves. Receptor expression was similar. Activation with phorbol myristate acetate resulted in increased expression of CR1 on neutrophils from normal and LAD-affected calves, but expression was almost twofold greater on neutrophils from normal calves. There was no difference between LAD-affected and normal calves in percentage of neutrophils that bound endogenous IgG and IgM. A greater percentage of neutrophils from normal calves bound exogenous IgM than did neutrophils from LAD-affected calves. Receptor expression for aIgG was greater on neutrophils from LAD-affected calves than on those from normal calves. Luminol-enhanced CL of neutrophils in response to IgG2 opsonized zymosan was not different between LAD-affected and normal calves. Results indicate increased binding and expression of Fc receptors for aIgG and decreased binding and expression for C3b and IgM on neutrophils from calves with LAD. Leukocyte adhesion deficiency may be compounded by added defects in the expression and binding of receptors for opsonins, such as C3b and IgM.

Investigation of the structure of equine articular cartilage link protein (LP) from individuals ranging in age from 1 to 15 years identified 3 distinct isoforms having molecular weights of 46,000, 43,000, and 41,000. The relative amounts of each of the 3 isoforms altered with age. The largest form did not change with age; however, amounts of the Mr 43,000 and 41,000 forms increased with increasing age. The results suggested that an accumulation, in the extracellular matrix of cartilage, of these 2 smaller products may have arisen from proteolytic cleavage. The complete amino acid sequence of the protein core was determined from complementary DNA products prepared by polymerase chain reaction amplification of cartilage LP mRNA. The sequence had 96% similarity with human LP and with that of other species for which the primary structure has been determined. This high degree of sequence conservation and the isoform data indicate that extracellular processing of LP occurs by similar mechanisms in various species. At the transcription level, equine chondrocytes were found to express LP as 2 abundant mRNA of 5.0 and 3.0 kb, and a smaller mRNA of 1.5 kb. Processing of the LP mRNA in horses, thus, appears to be similar to that found in other species investigated, and although multiple transcripts are present, the coding region remains unaltered and only 1 protein product is made.

Adhesion of equine spermatozoa to homologous oviduct epithelial cells (OEC) in vitro results in specific changes in spermatozoa and OEC function. To test the hypothesis that adhesion of spermatozoa affects protein synthesis and secretion by OEC, the following treatment groups were established in culture: OEC with culture medium only; control spermatozoa in culture medium only; OEC in coculture with spermatozoa; and OEC and spermatozoa in coculture, but physically separated by a microporous membrane. The experiment was replicated within each of 4 ejaculates from 3 stallions. De novo protein secretion by OEC was measured and compared by incorporation of [35S]methionine, and evaluated, using two-dimensional polyacrylamide gel electrophoresis and fluorography. Monolayers of OEC secreted a large number of proteins of molecular mass ranging from 14 to 205 kd. Adhesion of spermatozoa consistently caused reduced synthesis of 2 OEC secretory proteins and new or increased synthesis of 6 proteins. When spermatozoa and OEC were separated by a microporous membrane, some but not all of these changes were duplicated. Synthesis of 3 OEC secretory proteins, unaffected by binding of spermatozoa, was reduced when spermatozoa were prevented from contact with OEC by a microporous membrane. Adhesion of equine spermatozoa to homologous OEC monolayers and presence of equine spermatozoa resulted in qualitative and quantitative changes in synthesis and secretion of proteins by OEC. These changes have implications for storage, longevity, and maturation of spermatozoa.

Cortical bone concentrations of enrofloxacin were determined over time in dogs after SC administration of the drug. Nineteen healthy adult dogs were anesthetized and were given 2.5 or 5.0 mg of enrofloxacin/kg of body weight, SC. Serial serum and bone samples were obtained for determination of enrofloxacin concentrations at intervals until 8 hours after drug administration. Cortical bone samples were procured by surgical disarticulation of successive second phalanges. Additional cortical bone samples were taken from long bones in 4 dogs. Mean +/- SD peak serum enrofloxacin concentration was 0.54 +/- 0.10 micrograms/ml for the 2.5-mg/kg dosage and 0.97 +/- 0.34 micrograms/ml for the 5.0-mg/kg dosage. Serum concentration was significantly higher than bone concentration for each dosage. Mean peak bone concentrations reached 29% of peak serum values: 0.15 +/- 0.09 micrograms/g and 0.29 +/- 0.09 micrograms/g for 2.5-mg/kg and 5.0-mg/kg dosages, respectively. Serum concentration for the 5.0-mg/kg dosage was significantly greater than that for the 2.5-mg/kg dosage for all times, whereas bone concentrations for the 5.0-mg/kg dosage were significantly higher at all times after 180 minutes. For the duration of the study, cortical bone concentrations of enrofloxacin at either dosage exceeded the minimum inhibitory concentration (MIC) for the Enterobacteriaceae, but reliably exceeded the MIC for Staphylococcus sp only at the 5.0-mg/kg dosage. At no time did cortical bone concentrations of enrofloxacin exceed the MIC for Pseudomonas aeruginosa at either dosage. To validate extrapolation of data from the second phalanx to long bones and from anesthetized to awake dogs, 16 healthy dogs being euthanatized in unrelated studies were given 2.5 or 5.0 mg of enrofloxacin/kg, sc. These dogs were not anesthetized but were euthanatized at 60, 120, or 240 minutes after drug administration, and multiple cortical bone samples were taken. Antibiotic concentrations in the second phalanx were not significantly different from those in long bones. Comparison of enrofloxacin concentrations in cortical bone of awake and anesthetized dogs suggested no differences between groups. We concluded that general anesthesia and use of the antibiotic concentrations in the second phalanx as representative of those in long bones did not affect results of this study.

Pharmacokinetic and pharmacodynamic variables of flunixin were studied in calves after IV administration of the drug at a dose rate of 2.2 mg/kg of body weight. The anti-inflammatory properties of flunixin were investigated, using a model of acute inflammation; this involved surgically implanting tissue cages at subcutaneous sites and stimulating the tissue cage granulation tissue by intracavitary injection of carrageenan. The actions of flunixin on exudate concentrations of several substances related to the inflammatory process, including proteases (metalloprotease [active and total] and cysteine and serine proteases), enzymes (lactate dehydrogenase, acid phosphatase, and beta-glucuronidase [beta-glu]), eicosanoid (prostaglandin E2 [PGE2], leukotriene B4, and serum thromboxane B2 [TXB2]) concentrations, and bradykinin (BK)-induced edema, were investigated. Flunixin had a long elimination half-life--6.87 +/- 0.49 hours--and volume of distribution was 2.11 +/- 0.37 L/kg, indicating extensive distribution of the drug in the body. Body clearance was 0.20 +/- 0.03 L/kg/h. Flunixin exerted inhibitory effects on serum TXB2 and exudate PGE2 concentrations, B-glu activity, and BK-induced swelling. Other enzymes and inflammatory mediators were not significantly affected. Pharmacokinetic/pharmacodynamic modeling of the data revealed similar mean concentration producing 50% of the maximal effect values for inhibition of exudate PGE2 and beta-glu and of BK-induced swelling (0.070 +/- 0.006, 0.064 +/- 0.040, and 0.061 +/- 0.030 microgram/ml), respectively). A lower concentration producing 50% of the maximal effect value was obtained for inhibition of serum TXB2 concentration (0.023 +/- 0.004 microgram/ml). Differences also were observed in equilibration half-life for these actions, suggesting the existence of 3 distribution compartments correlating with 3 sites of action--a central compartment and shallow and deep peripheral compartments. Pharmacokinetic/pharmacodynamic modeling proved to be a useful analytical method, providing a quantitative description of in vivo drug pharmacodynamics and indicating possible mechanisms of action.

Health and ruminal variables were intensively measured during adaptation to grain-based diets in 6 beef cattle with fistulated rumens. The cows had been maintained on prairie grass hay-supplemented diets, and were converted to a grain-based finishing ration by feeding each successive diet (diets 1-4, respectively) for a period of 7 days. Each cow was evaluated and samples were obtained 3 times each day for the first 5 days that each diet was fed. Health variables monitored were rectal temperature, pulse, respiratory and rumen motility rates, fecal consistency, demeanor, blood pH, and blood glucose and L(+) lactate concentrations. Ruminal variables monitored were pH and glucose, DL-lactate, and volatile fatty acid concentrations of rumen contents. Data were analyzed by use of a multivariate ANOVA. We determined that most of the health variables were within reference rang limits throughout the adaptation period; however, analysis of pulse and respiratory rates indicated that diets 2 and 4 were stressful. Although blood pH continually decreased during feeding of the 4 diets (7.38 to 7.30), blood L(+) lactate and glucose concentrations had large increases only within diet 4. The pH of ruminal contents decreased progressively from 6.8 to 5.3. Rumen glucose concentration was low (< 1 micromole/ml), except with diet 4 in which values were 8 times higher than for other diets. By the end of the study, the ruminal contents of all animals were acidic (pH < 5.5), and, on the basis of higher than background amounts of ruminal glucose and DL-lactate, it was determined that rumen microbial equilibrium had not yet been achieved. Analysis of results of this study suggested that ruminal imbalance could be evaluated by monitoring pulse and respiratory rates, blood pH, and blood glucose concentrations. Assessment of the rumen alone could be accomplished by monitoring the variables of rumen pH, rumen glucose, and DL-lactate concentrations. Respiratory rate, blood and rumen content pH, and blood L(+) lactate concentrations were significantly (P < 0.001) affected by time after feeding.

Microcystin and related toxic peptides produced by cyanobacteria (blue-green algae) are potent and selective inhibitors of protein phosphatases 1 and 2A. We adapted existing enzymatic techniques to analyze the liver of rainbow trout after oral administration of hepatotoxic cyanobacteria. Liver tissue was removed 3 and 12 hours after treatment, and phosphatase activity was determined in liver extracts, using a specific phosphoprotein substrate. In all samples from fish exposed to toxic cyanobacteria, phosphatase activity was suppressed, whereas the control enzyme, lactate dehydrogenase, present in the same liver extract, was not affected by cyanobacteria. Thus, experimental poisoning by hepatotoxic cyanobacteria resulted in an abnormally low ratio of phosphatase to lactate dehydrogenase activity in the liver extracts. These results indicate that specific inhibition of phosphatases 1 and 2A may provide a useful diagnostic tool to determine the early effects of cyanobacteria toxic peptides directly in liver samples from poisoned animals. Although this test was developed with rainbow trout, it should be possible to extend the analysis of liver phosphatase activity to other species, including sheep and cattle, which are frequently affected by hepatotoxic cyanobacteria.