The cause of species difference in the susceptibility of erythrocytes to L-sorbose, and the difference in the hemolytic effect of sorbose on high potassium-containing (HK) and low potassium-containing (LK) canine erythrocytes were examined. L-sorbose was phosphorylated in canine erythrocytes, but not in human erythrocytes. Furthermore, sorbose-1-phosphate, a metabolite of L-sorbose, strongly inhibited the hexokinase of LK canine erythrocytes, but not that of HK canine erythrocytes. These results strongly indicated that inhibition of hexokinase by sorbose-1-phosphate in LK erythrocytes induced severe glycolytic limitation in these cells, resulting in hemolysis, and that HK erythrocytes are resistant to sorbose-induced hemolysis because these cells have a high hexokinase activity.

Alterations in the size and functions of porcine alveolar macrophages exposed to sublytic amounts of heat-labile, hemolytic cytotoxin produced by Actinobacillus pleuropneumoniae (App) serotype 1, strain HS54 into the culture medium were studied in vitro. Alveolar macrophages were sensitive to the cytotoxin; treatment of the macrophages with low concentrations of cytotoxin (0.016 hemolytic unit) resulted in severe, irreversible cell swelling. However, high doses of cytotoxin (2.0 hemolytic units) were required to cause substantial cell death, as indicated by the influx of propidium iodide into and release of lactate dehydrogenase from cells. Macrophages exposed to low, sublytic doses of cytotoxin failed to migrate toward chemoattractant, were unable to attach to glass, and failed to phagocytize optimally opsonized erythrocytes. Macrophages already attached to glass surfaces detached when exposed to sublytic doses of cytotoxin. The swelling and impairment of functions of alveolar macrophages observed in this study could not be attributed to endotoxic effects, because heat treatment of the cytotoxin preparation for 60 minutes at 60 C resulted in complete loss of cytotoxicity. We conclude that sublytic doses of heat-labile, hemolytic cytotoxic substances produced by App depress alveolar macrophage function at concentrations likely to develop in association with acute pulmonary infection with App. The Apx (A pleuropneumoniae Rtx toxins) exotoxins secreted by the bacteria into culture medium were considered responsible for the toxic activity of the cytotoxin preparation. The Apx of the App field strain used in this study were likely to be similar to those of serotype-1 reference strain (S4707). Analysis by use of DNA-DNA hybridization indicated that genomic DNA of the field strain contained sequences similar to those encoding structural protein of ApxI (apxIA) and ApxII (apxIIA) of the serotype-1 reference strain. Therefore, Apx produced by the field strain of App used in this study are likely to be of similar pathogenic importance worldwide.

Equine oxyntic mucosal cells were obtained by sequential exposure to pronase and collagenase. Acid production by parietal cells was assessed by uptake of [14C]aminopyrine (AP), a weak base that accumulates in intracellular acidic spaces. Incubation for various times revealed a maximal AP uptake at 10 minutes for histamine and carbachol. Similar secretagogue responses were observed for parietal cells from the mucosal cell preparation or after enrichment by elutriation. Histamine and isobutyl-methylxanthine (IBMX) stimulated AP uptake with a dose-dependent response and maximal effective concentration of 100 micromolar. Carbachol, 1 to 100 micromolar, and pentagastrin (PG), 1 to 1,000 nM, were ineffective stimulants of AP uptake. The AP uptake values for 100 micromolar IBMX, 1 micromolar carbachol, or 100 nM PG were 77 +/- 6%, 50 +/- 3.2%, and 40 +/- 4.5%, respectively, of that observed with maximal stimulation by 100 micromolar histamine (mean SEM, n = 4 to 14). Uptake of AP by nonstimulated control cells was 36 +/- 3.6% of maximal histamine stimulation. The AP accumulations during control conditions and after stimulation with 100 micromolar histamine and IBMX, 1 micromolar carbachol, or 100 nM PG were 1.18 +/- 0.39, 2.81 +/- 0.85, 1.93 +/- 0.48, 1.44 +/- 0.36, and 1.23 +/- 0.33 pmol of AP/10(5) parietal cells, respectively. Individual histamine dose-response curves were shifted to the right by increasing ranitidine and cimetidine concentrations (0.1 to 50 micromolar). These results indicate that isolated equine parietal cells are maximally stimulated by histamine and minimally stimulated by carbachol and PG.

High serum alkaline phosphatase (ALP) activity is considered a sensitive marker of cholestasis in most mammalian species, including dogs. Induction of high serum ALP activity in association with cholestasis is dependent on high hepatic bile acids concentrations. Treatment of dogs with glucocorticoids also results in high serum ALP activity. The possible causal relation between serum ALP activity and bile acids concentration was investigated in dogs treated with glucocorticoids. The relation of glucocorticoid treatment to changes in the activity of individual ALP isoenzymes, alanine transaminase (ALT) and gamma-glutamyltransferase (GGT) also was investigated. Eight conditioned dogs were given 4 mg of prednisone/kg of body weight, IM, daily for 10 days. Blood samples were taken prior to treatment and on treatment days 3, 5, 7, and 10. Liver tissue was then taken from each dog. Serum total ALP activity was significantly (P < 0.05) high at day 3 in prednisone-treated dogs. Isoenzyme analysis indicated that this increase was attributable to an increase in the liver ALP isoenzyme (LALP). Significant increases in serum corticosteroid-induced ALP (CALP) and bone ALP were first observed on days 7 and 10, respectively. Serum ALT and GGT activities were significantly increased by day 5. Increased serum or hepatic tissue bile acids concentrations were not observed in prednisone-treated dogs, compared with values in 8 clinically normal (control) dogs, but were high in 3 dogs with complete bile duct ligation. Hepatic activities of LALP, CALP, and GGT were higher in prednisone-treated dogs than values in controls, indicating probable increased hepatic synthesis of these enzymes. Hepatic ALT activity was not increased. The ratio of serum to tissue LALP activity was increased in prednisone-treated dogs, compared with values in controls, indicating that LALP may have been preferentially released into serum. There was no difference in the ratio of serum to liver GGT activity between prednisone-treated dogs and controls. The LALP and GGT ratios were increased in bile duct-obstruction dogs. It was concluded that, although LALP is the principal ALP isoenzyme in serum during the first 10 days of prednisone treatment, hepatic bile acid concentrations are not increased and, therefore, are not likely to be responsible for induction and release of ALP into serum. Prednisone may, therefore, be directly responsible for induction of ALP activity in dogs treated thusly.

Polymorphonuclear neutrophils (PMN) from 4 cows were preincubated (30 minutes, 37 C) in either actinomycin D (100 micrograms/ml) or puromycin (10 micrograms/ml), inhibitors of mRNA transcription and protein translation, or in medium 199. The PMN were incubated for a further 4.5 hours in medium containing 100 U of recombinant bovine interferon-gamma (rboIfn-gamma). The PMN were then incubated with bovine IgG1, IgG2, IgM, or aggregated IgG (aIgG; 4 C, 12 hours) for flow cytometric analysis, using fluoresceinated isotype-specific antibody. The percentage of PMN binding the ligand and the logarithmic mean fluorescent channel (LMFC), an indicator of the amount of receptor (R) expression, were recorded. Competitive inhibition of ligand binding was measured by incubating PMN with fluoresceinated IgG2 in the presence or absence of 100-fold excess of IgG1, IgG2, and aIgG. Activation with rboIfn-gamma induced a 4.5-fold increase in binding of IgG1 and a fivefold increase in LMFC for IgG2. These increases were inhibited by actinomycin D and puromycin. Percentage of PMN binding aIgG decreased after activation by rboIfn-gamma. Interferon-gamma treatment did not affect binding or LMFC of IgM. However, binding of IgM was reduced by treatment with actinomycin D. Binding of fluoresceinated IgG2 was inhibited by unlabeled IgG1, IgG2, and aIgG. Results indicate that bovine PMN Fc receptors (FcR) for IgG1 and IgG2 were rboIfn-gamma inducible, that induction required de novo transcription and translation, that a heterogeneous population of FcR exist on bovine PMN, and that IgG1 and IgG2 share a common FcR. Further, bovine PMN are capable of gene activation and are responsive to changes in their environment, thus being amenable to modulation for effective pathogen destruction.

Diamine oxidase (DAO), an enzyme of small intestinal origin, is released from mucosal storage sites by IV administration of heparin, to yield the plasma postheparin DAO (PHD) curve. The PHD curve is diminished when mucosal surface area is lost, and baseline (without heparin) plasma DAO activity increases when mucosal storage sites are damaged. Plasma DAO activity was measured after 2 doses of heparin were administered Iv in healthy, conscious horses. In anesthetized horses, the PHD curve was studied: during sham small intestinal surgery, and during venous strangulation obstruction (VSO) of the distal 50% of the small intestine. In a third group of anesthetized horses, baseline plasma DAO activity (without heparin) was measured during vso of the distal 50% of the small intestine for 90 minutes, followed by reperfusion for 90 minutes. Postheparin plasma DAO curves in conscious horses were similar to those reported in other species Horses with VSO had a similar PHD curve as did sham-operated controls at all times, except at 15 minutes, when plasma DAO activity was significantly (P < 0.05) greater in the vso group. Horses with VSO and reperfusion had no change in baseline plasma DAO activity throughout the study. Peritoneal fluid DAO activity remained low throughout the study, but increased slightly in horses with VSO that received heparin, possibly because of DAO from extravasated blood in the peritoneal fluid. Results indicated that the plasma DAO response to IV administered heparin in horses is similar to that in other mammals, but, unlike other species, baseline and postheparin DAO activities did not change as expected after small intestinal vascular obstruction and mucosal injury. There may be additional sources of DAO in horses, the type of injury induced was not of sufficient magnitude to affect storage sites of DAO, or the circulatory changes induced by vso might have altered tissue delivery of heparin.

Plasma concentration of penicillin G was evaluated in beef steers after administration of either a combination of benzathine penicillin G and procaine penicillin G in a 1:1 mixture at a dosage of 9,000 U/ kg of body weight, IM (n = 5), 24,000 U/kg, IM (n = 5), or 8,800 U/kg, SC (n = 5), or benzathine penicillin G alone at a dosage of 12,000 U/kg, IM (n = 7). Plasma concentration of penicillin G was measured by use of a high-performance liquid chromatography assay that had a limit of determination of 0.005 micrograms/ml. At a dosage for this combination of 9,000 U/kg IM, and 8,800 U/kg, SC, which are approved label recommendations in Canada, and the United States, respectively, mean (+/- SEM) peak plasma concentration was 0.58 (+/- 0.15) and 0.44 (+/- 0.02) micrograms/ml, respectively. Although plasma penicillin concentration was quantifiable for 7 days in the steers that received 9,000 U/kg, IM, and for 4 days in the steers that received 8,800 U/kg, SC, the concentration was < 0.1 micrograms/ml in both groups after the first 12 hours. After administration of the combination at dosage of 24,000 U/kg, IM, there was an initial peak plasma concentration at approximately 2 hours; thereafter, plasma concentration decreased slowly, with half-life of 58 hours. Although plasma penicillin G concentration was quantifiable for 12 days at this dosage, concentration was < 0.1 micrograms/ml after the first 48 hours. After the initial 48 hours, plasma concentration of penicillin was of similar magnitude and decreased at similar rate for the combination at dosage of 24,000 U/ kg and for 12,000 U/kg of benzathine penicillin G alone. Most of the plasma penicillin G concentration in the first 24 hours after administration of a 1:1 combination of benzathine penicillin G and procaine penicillin G is attributable to absorption of procaine penicillin G. After the first 48 hours, most of the plasma drug concentration appeared to be produced by absorption of penicillin G from benzathine penicillin G. Absorption of benzathine penicillin G produces quantifiable plasma penicillin G concentrations for several days, but they are below the level of susceptibility for most bacteria.