Evaluation of a rapid PCR-based method for the detection of animal material

A rapid PCR-based analytical method for detection of animal-derived materials in complete feed was developed. Using a commercially available DNA forensic kit for the extraction of DNA from animal feed, a sensitive method was developed that was capable of detecting as little as 0.03% bovine meat and bone meal in complete feed in under 8 h of total assay time. The reduction in assay time was accomplished by reducing the DNA extraction time to 2 h and using the simpler cleanup procedure of the kit. Assay sensitivity can be increased to 0.006% by increasing the DNA extraction time to an overnight incubation of approximately 16 h. Examination of dairy feed samples containing either bovine meat and bone meal, porcine meat and bone meal, or lamb meal at a level of 0.1% (wt/wt basis) suggested that this method may be suitable for regulatory uses. The adoption of this commercially available kit for use with animal feeds yields an assay that is quicker and simpler to perform than a previously validated assay for the detection of animal proteins in animal feed.

Development of a polymerase chain reaction-based method to identify species-specific components in dog food

OBJECTIVES

To determine whether there is a relationship between species-specific mitochondrial DNA (mtDNA), especially canine and feline mtDNA, and detectable amounts of pentobarbital in previously analyzed dog food samples.

SAMPLE POPULATION

31 dog food samples previously analyzed for pentobarbital (limit of detection, 1 microg/kg).

PROCEDURE

Polymerase chain reaction (PCR) analysis was performed on dog food samples by use of PCR primers specific for either canine, feline, equine, bovine, porcine, ovine, or poultry mtDNA.

RESULTS

PCR amplicons specific for feline or canine mtDNA at a 0.007% (70 microg/g [wt/wt basis]) or 0.0007% (7 microg/g) level, respectively, were not found in the 31 dog food samples. Most of the 31 dog food samples had a PCR amplicon on PCR analysis when a PCR primer set capable of simultaneously detecting mtDNA of cows, pigs, sheep, goats, deer, elk, and horses was used. Results of PCR analysis by use of primers specific for bovine, swine, sheep and goat, or horse mtDNA revealed amplicons specific for bovine or swine mtDNA only in 27 of the 31 samples. Analysis of the remaining 4 samples failed to yield amplicons for any mammalian mtDNA. Pentobarbital was detected in 2 of these 4 samples. Results of PCR analysis correlated with the stated ingredient list for most, but not all samples.

CONCLUSIONS AND CLINICAL RELEVANCE

Because canine and feline mtDNA were not found in a set of retail dog food samples, these results indicate that the source of pentobarbital in dog food is something other than proteins from rendered pet remains.

Inflammatory Cytokines, Pleuropneumonia Infection and the Effect of Dexamethasone

OBJECTIVES

Actinobacillus pleuropneumoniae causes an often fatal infection of swine due to pleuropneumonia. To determine if inflammatory cytokines are associated with A. pleuropneumoniae-induced pneumonia, infected and noninfected animals were concomitantly administered saline or dexamethasone.

METHODS

Twenty-four swine were treated with saline, A. pleuropneumoniae, dexamethasone, or A. pleuropneumoniae and dexamethasone (n = 6). The plasma levels of TNF-alpha, IL-1beta, IL-6, IL-8, and IL-10 were examined through time of necropsy (72 h). Gross pathology and histopathology was performed on all animals.

RESULTS

Dexamethasone had no effect on A. pleuropneumoniae-induced increases in lung/body weight ratios. Gross pathology of the infected pigs included fibrinous pleuropneumonia with necrosis and hemorrhage in a focal to a multifocal pattern. Histopathology of infected pig lungs revealed necrotizing extensive, fibrinopurulent pneumonia with edema and fibrinopurulent pleuritis. Plasma IL-6 levels were elevated in A. pleuropneumoniae-infected animals beginning 6 h after infection. Dexamethasone treatment did not alter A. pleuropneumoniae-induced plasma IL-6 levels. A. pleuropneumoniae infection did not elicit plasma levels of TNF-alpha, IL-1beta, IL-8, or IL-10.

CONCLUSION

These results suggest that the pneumonia caused by A. pleuropneumoniae infection is not due to the release of systemic inflammatory cytokines.

Effect of oral administration of low doses of pentobarbital on the induction of cytochrome P450 isoforms and cytochrome P450-mediated reactions in immature Beagles

OBJECTIVE

To determine the effect of oral administration of low doses of pentobarbital on cytochrome P450 (CYP) isoforms and CYP-mediated reactions in immature Beagles.

ANIMALS

42 immature (12-week-old) Beagles.

PROCEDURE

Dogs were grouped and treated orally as follows for 8 weeks: low-dose pentobarbital (50 microg/d; 4 males, 4 females), mid-dose pentobarbital (150 microg/d; 4 males, 4 females), high-dose pentobarbital (500 microg/d; 4 males, 4 females), positive-pentobarbital control (10 mg/kg/d; 2 males, 2 females), positive-phenobarbital control (10 mg/kg/d; 2 males, 2 females), and negative control (saline 10.9% NaCl] solution; 5 males, 5 females). Serum biochemical and hematologic values were monitored. On necropsy examination, organ weights were determined, and histologic evaluation of tissue sections of liver, kidney, small intestine, testes, epididymis, and ovaries was performed. Hepatic and intestinal drug-metabolizing enzyme activities were measured, and relative amounts of CYP isoforms were determined by western blot analysis.

RESULTS

The amount of a hepatic CYP2A-related isoform in dogs from the high-dose pentobarbital treatment group was twice that of dogs from the negative control group. CYP2C was not detectable in small intestinal mucosa of dogs from the negative control group; measurable amounts of CYP2C were found in dogs from the various (low-, mid-, and high-dose) pentobarbital treatment groups and from positive-pentobarbital and positive phenobarbital control groups. Several CYP-mediated reactions increased in a dose-dependent manner. The lowest calculated effective dose of pentobarbital ranged from 200 to 450 microg/d.

CONCLUSIONS AND CLINICAL RELEVANCE

Several CYP isoforms and their associated reactions were induced in dogs by oral administration of low amounts of pentobarbital.

Immunotoxicity of aflatoxin B1 in rats: effects on lymphocytes and the inflammatory response in a chronic intermittent dosing study

We investigated the effects of aflatoxin B1 (AFB1) on isolated splenic lymphocytes and the histo-morphologic changes in the spleens and liver of Fisher-344 male rats. Weaned animals were fed chow diets that contained 0, 0.01, 0.04, 0.4, or 1.6 ppm AFB1, using an intermittent dosing regimen (4 weeks on and 4 weeks off AFB1), for 40 weeks. An additional group of animals was fed the 1.6 ppm AFB1 diet continuously. The intermittent dosing regimen was designed to evaluate effects of cumulative dose and exposure for risk assessment comparisons. The percentages of T and B cells were affected as shown by flow cytometric analysis after the dosing cycles. The observed changes appeared to reverse or compensate to some extent after the off cycles. Lymphocytes were stimulated in culture for analysis of the production of IL-2, IL-1, and IL-6. Significantly increased production of IL-1 and IL-6 was seen in the second dosing cycle (12 weeks) and the second "off" cycle (16 weeks) at the higher doses. Inflammatory infiltrates were seen in the liver after eight weeks of continuous and intermittent dosing and were increased in size and number at 12 weeks in both 1.6 ppm dose groups correlating with the peak production of Il-1 and IL-6. We concluded that AFB1 effects on the immune system can be either stimulatory or suppressive dependent on a critical exposure window of dose and time. Immune cells in spleen such as T-lymphocytes and macrophages, both important mediators of inflammatory responses to tissue damage, were affected differently in the continuous and intermittent exposures to AFB1.

Characterization of a polymerase chain reaction-based approach for the simultaneous detection of multiple animal-derived materials in animal feed

In this study, a polymerase chain reaction (PCR) primer set capable of amplifying a mitochondrial DNA segment of multiple species (cattle, sheep, goats, deer, and elk) whose rendered remains are prohibited from being fed to ruminants was characterized. However, the primer set also amplifies DNA derived from the rendered remains of pigs and horses, which are exempt from the feed ban. PCR amplicons derived from pig DNA have a restriction endonuclease site recognized by Hinf1, while the horse DNA-derived amplicon has a unique restriction endonuclease site recognized by HypCH4III. This "universal" PCR primer produced an amplicon with DNA extracted from dairy feed containing either bovine meat and bone meal or pig blood meal. Enzymatic digestion of the PCR amplicons from these feed samples with Hinf1 resulted in cleavage products only from samples containing pig blood meal. However, Hinf1 digestion of these amplicons was not complete. Further analysis of the pig blood meal with primers specific for bovine or porcine DNA demonstrated the presence of both bovine- and porcine-derived DNA. Enzymatic digestion confirmed these findings. Additional testing was conducted with dry dog food samples labeled as containing either lamb, chicken, turkey, or chicken and fish. The universal PCR primer produced an amplicon only for the dog food containing lamb meal. This paper is the first to describe a simplified approach for the detection of the prohibited species of concern in the feed ban.

Inflammatory mediator production in swine following endotoxin challenge with or without co-administration of dexamethasone

The inflammatory response in swine challenged with lipopolysaccharide (LPS) has only been partially characterized. As swine are increasingly used in biomedical research, it is important to determine if they respond to endotoxin challenge in a manner similar to other model systems. Accordingly, 24 Poland China x Landrace barrows were treated with saline, LPS, dexamethasone, or LPS and dexamethasone, with six animals in each treatment group. The kinetics of TNFalpha, IL-1beta, IL-6, IL-8, IL-10, nitric oxide (nitrate/nitrite), and neopterin production in swine plasma were examined at 1, 3, 6, 9, and 24 h after acute LPS challenge. Lipopolysaccharide increased plasma TNFalpha levels, which peaked 1 h post-challenge. Dexamethasone decreased LPS-induced TNFalpha by approximately 60%. Plasma IL-6 levels peaked 3 h post-LPS challenge, returning to basal levels by 9 h. Swine given both LPS and dexamethasone had minimal IL-6 levels. Control and dexamethasone-only treated animals never exhibited systemic TNFalpha or IL-6 levels. Lipopolysaccharide increased plasma IL-10 1 h after challenge. Dexamethasone did not alter plasma IL-10 levels in LPS-challenged swine. Interleukin-1beta was constitutively present in plasma and was not altered by any combination of treatments. Plasma IL-8 was not observed in any treatment group. Plasma nitrate/nitrite levels were maximal 24 h post-challenge. Dexamethasone treatment prevented increases in plasma nitrate/nitrite levels in LPS-treated animals. Lipopolysaccharide induced levels of neopterin; dexamethasone served to further increase plasma neopterin levels in LPS-challenged animals. The discordant regulation of inflammatory mediators suggests that the immunological responses by swine to LPS are distinct from the responses seen in rodent and human studies.

Long-term recombinant porcine somatotropin (PST) treatment mitigates the responses to subchronic lipopolysaccharide in swine

The effect of multiple lipopolysaccharide (LPS) challenges in swine undergoing long-term treatment with porcine somatotropin (PST) was determined. Changes in aspartate serine transaminase (AST) occurred only at 24h following the first LPS challenge dose (P<0.05), while PST treatment moderated any change from occurring. Nonesterified free fatty acid (NEFA) levels were elevated in PST treated animals for the first 3 days following daily LPS treatment (P<0.05), while LPS treatment alone had no effect on plasma NEFA levels. Plasma urea nitrogen (PUN) levels were unchanged by LPS following the initial LPS challenge, but were decreased following the second challenge dose (P=0.014). These changes were long lasting, with a return to normal PUN levels not evident until Day 6. The PST treatment mitigated changes in PUN (P<0.05) when LPS was administered. Haptoglobin plasma levels, along with lipid peroxide production were not affected by LPS challenge or PST administration. LPS challenge reduced the levels of immunoreactive heat shock protein 70 (HSP70) throughout the entire challenge period (P<0.001). PST-LPS animals had normal levels of this protein. The results of the present study demonstrate that long-term PST treatment mitigates the adverse effects of subchronic LPS administration.

The effect of endotoxin and dexamethasone on enrofloxacin pharmacokinetic parameters in swine

The impact of Escherichia coli-derived lipopolysaccharide (LPS) on the pharmacokinetic parameters of enrofloxacin in swine was assessed to determine whether this model would substitute for a pleuropneumonia infection model for pharmacokinetic evaluation of drugs. All animals received a single i.v. dose of enrofloxacin (5 mg/kg). Half the animals also received dexamethasone (0.5 mg/kg) to determine the impact of inflammation on any changes in enrofloxacin pharmacokinetics, as most of the effects of LPS are due to elaboration of inflammatory mediators. Administration of LPS alone (2.0 microg/kg) was associated with a decrease in clearance of enrofloxacin. Volume of distribution at steady state was increased in the dexamethasone-treated animals. The terminal elimination half-life of enrofloxacin was significantly increased in the LPS group. Dexamethasone administration, either alone or in combination with LPS challenge, increased the volume of distribution both at steady state and during the elimination phase. Lipopolysaccharide challenge did not affect the volume of distribution. Lipopolysaccharide challenge did not affect urinary excretion of enrofloxacin but did increase the urinary excretion of its principal metabolite, ciprofloxacin. However, the increased excretion did not begin until 24 h after administration of enrofloxacin. Because these pharamcokinetic results are different from those obtained with the pleuropneumonia model using the bacteria Actinobacillus pleuropneumoniae, the results of this study demonstrate that LPS is not a generic substitute for infection for the pharmacokinetic evaluation of drugs.

Effects of live attenuated and killed Salmonella vaccine on T-lymphocyte mediated immunity in laying hens

The impact of live and killed Salmonella vaccines on cell-mediated immunity (CMI) was investigated in 18- and 32-week-old White Leghorn chickens, by assessing splenic lymphocyte proliferation, expression of IL-2 mRNA in concanavalin A (Con A) stimulated cells and flow cytometric analysis of cell subpopulations. Con A and Salmonella enteritidis (SE) flagella induced proliferation of splenocytes were enhanced in the 18- and 32-week-old chickens treated with live vaccine, compared to the corresponding control chickens. Among the killed vaccine treated birds, Con A-mediated response was higher in the 18-week-old chickens compared to the corresponding control birds. Increased proliferation was accompanied by increased CD4 and reduced CD8 and gammadelta T-lymphocytes in the 18-week-old live vaccine treated chickens. Relative expression of IL-2 mRNA in Con A-stimulated splenocytes from 18-week-old birds was not affected by vaccine treatment. Overall, live vaccine was more effective in increasing the lymphocyte proliferation to Con A as well as SE antigen. This enhanced CMI may prove beneficial in protecting chickens against SE infection.

Influence of porcine Actinobacillus pleuropneumoniae infection and dexamethasone on the pharmacokinetic parameters of enrofloxacin

The impact of Actinobacillus pleuropneumoniae (APP) infection in swine on the pharmacokinetic parameters of enrofloxacin were determined. Twenty-four animals were used in a 2 x 2 factorial of treatment groups (six animals per group) to determine the impact of APP-induced inflammation and the anti-inflammatory drug dexamethasone on enrofloxacin pharmacokinetic parameters. All animals received enrofloxacin as a single intravenous dose (5 mg/kg). Administration of dexamethasone was associated with an increase in clearance of enrofloxacin Clearance of enrofloxacin was not affected by APP. Volume of distribution at steady state was significantly increased in the dexamethasone-treated pigs. Volume of distribution at steady state was decreased by APP infection. Dexamethasone significantly increased the terminal elimination half-life of enrofloxacin. APP infection decreased the terminal elimination half-life of enrofloxacin in the infected pigs. Infection and dexamethasone significantly decreased the urine enrofloxacin/creatinine and ciprofloxacin/creatinine ratios. This study shows that APP infection does affect plasma pharmacokinetic parameters. Dexamethasone and APP infection may reduce renal clearance of enrofloxacin with a compensatory increase in intestinal clearance. Neither infection nor dexamethasone altered the metabolism of enrofloxacin to ciprofloxacin, the principal metabolite of enrofloxacin.

Effects of pentoxifylline on inflammatory cytokine expression and acute pleuropneumonia in swine

Pentoxifylline, a methylxanthine derivative and nonspecific type 4 phosphodiesterase inhibitor, has been used to improve survival of animals with sepsis and to attenuate lung injury in acute lung inflammation. The purpose of this study was to examine whether pentoxifylline would inhibit the expression of inflammatory cytokines, particularly tumor necrosis factor alpha (TNF), and thereby decrease the pathophysiology of acute porcine pleuropneumonia. E. coli lipopolysaccharide (LPS) and bacterial extracts of A. pleuropneumoniae--induced elevations in TNF mRNA which were fully abrogated by addition of pentoxifylline in both alveolar macrophage and neutrophil cultures. A 30% reduction in the level of LPS-induced interleukin (IL)-1beta mRNA levels also was achieved in macrophages. Pentoxifylline did not affect either IL-1alpha or IL-8 expression in vitro. Pentoxifylline therapy in vivo significantly reduced the number of band neutrophils in swine but did not reduce the pathology associated with pleuropneumonia, including changes in serum zinc, iron, or haptoglobin. Neither did it alter TNF, IL-1, IL-6, or IL-8 expression. Measurement of pentoxifylline and its metabolites in pig sera suggested that efficacious doses of pentoxifylline were probably not achieved in vivo. However, subcutaneous doses of pentoxifylline higher than 25 mg/kg produced transient diarrhea, vomiting, and tremors. These results suggest that pentoxifylline is an effective pharmacological tool for the dissection of cytokine regulation in vitro, but inhibitory concentrations may not be achievable for in vivo pharmacological use in swine.

Identification of multiple constitutive and inducible hepatic cytochrome P450 enzymes in market weight swine

Constitutive swine enzymes analogous to human/rat cytochrome P450 (CYP) isoforms 1A2, 2A6, 2B1/2/6, 2D6, 2E1, 3A1, and 4A1/3 were detected by Western blot analysis. Swine 2E1 has a molecular weight greater than rat 2E1; swine 2B2 has a molecular weight similar to human 2B6. An induction cocktail containing beta-naphthoflavone, phenobarbital, and dexamethasone induced immunoreactive homologs of 1A1, 1A2, 2B1, 2B2, 3A1, and 3A2. Although the P450 content was increased by induction, there was no difference in the Soret lambda(max). Swine 1A1 has a lower molecular weight than swine 1A2 and rat 1A1. A swine 2B1 homolog was seen after induction, with a molecular weight that was lower than rat 2B1 but higher than swine 2B2. Induction did not augment swine 2B2 levels. The 3A homologs have molecular weights similar to their rodent counterparts. Following induction, swine 3A1 levels increased and were accompanied by the appearance of swine 3A2. Induction had no effect on expression of 2A6, 2B6, 2D6, 2E1, or 4A1/3. Enzyme induction increased the specific activities (nmol/min/mg) of substrates specific for 1A (7 of 7 substrates tested), 2A (2/2), 2B (5/5), 2C (1/3), 2D (3/4), 2E (3/3), 3A (3/5), and 4A (1/1). Although the specific activities of the 2E substrates increased, the turnover number for hydroxylation of chlorzoxazone was unchanged and that of p-nitrophenol and aniline were depressed in induced pigs. These results show that swine CYP isoforms are similar to those identified in human and rodents, but they are also different in many ways.

Differential cytokine mRNA expression in swine whole blood and peripheral blood mononuclear cell cultures

The kinetics of interleukin-2 (IL-2), IL-6, IL-8 and IL-10 gene expression in concanavalin A (Con A)-activated whole blood (WB) and peripheral blood mononuclear cell (PBMC) cultures were examined using reverse transcriptase-polymerase chain reaction (RT-PCR). Unstimulated PBMC or WB cultures failed to show increases in basal cytokine PCR amplicon levels for any cytokine examined. PBMC cultures demonstrated peak expression of IL-2, IL-6, IL-8 and IL-10 mRNA levels at 12, 24, 24 and 6h, respectively. WB cultures exhibited peak IL-2, IL-6, IL-8 and IL-10 mRNA levels at 24, 12, 6 and 24h, respectively. PBMC cultures consistently exhibited higher levels of IL-2 mRNA at all times examined than did WB cultures. WB cultures consistently had higher levels of IL-6 mRNA than PBMC cultures. IL-8 and IL-10 protein levels in PBMC cultures were first detected 12h after stimulation and continued to increase in concentration through 48h. In WB cultures, IL-8 and IL-10 protein levels were first noted at 12 and 6h, respectively. WB culture IL-8 and IL-10 levels quickly reached equilibrium after being detected and remained at levels lower than those noted in PBMC cultures. These results show WB cultures represent an approach with reduced cost and time when compared to traditional cell culture and isolation methods. It may also produce an in vitro test system that more closely resembles in vivo conditions.

Validation of a polymerase chain reaction method for the detection of rendered bovine-derived materials in feedstuffs

This study validated a polymerase chain reaction-based method for the detection of a specific bovine mitochondrial gene derived from rendered bovine tissues and admixed with complete animal feed. Four laboratories participated in this effort: one state laboratory and three Food and Drug Administration (FDA) laboratories, including one FDA field laboratory. The protocol used a statistical approach of 90% probability, with a 95% confidence interval for determining acceptable rates of false-positive and false-negative samples. Each participating laboratory analyzed 30 samples of feed each containing 0, 0.125, and 2.0% bovine meat and bone meal (BMBM), for a total of 90 feed samples. The samples were randomized such that the analysts were unaware of the true identity of the test samples. The results demonstrated that all laboratories met the acceptance criteria established for this protocol. The overall rates of false-negative results were 0.83% (1/120) at the level of 0.125% BMBM and 1.67% (2/120) at the level of 2% BMBM. The overall rate of false-negative results for all levels of BMBM was 1.25% (3/240). The rate for false-positive results was 0.83%.

Evaluation of pulmonary alveolar epithelial integrity by the detection of restriction to diffusion of hydrophilic solutes of different molecular sizes

The rate of transfer of a hydrophilic solute from the alveoli to pulmonary blood following inhalation as an aerosol depends on the molecular size of the solute and the permeability of the alveolar epithelium. The value of this measurement for assessing damage to the epithelium in lung disease is compromised by cigarette smoking, which accelerates clearance by unknown mechanisms. The rates of clearance of (99m)Tc-labelled diethylenetriaminepenta-acetic acid (DTPA) (molecular mass 492 Da) and (113m)In-labelled biotinylated DTPA (B-DTPA) (molecular mass 1215 Da) were monitored simultaneously by dynamic gamma-radiation camera imaging following simultaneous inhalation, and compared between eight normal non-smoking subjects and nine habitual cigarette smokers. The clearance rates of DTPA were 0.95 (S.D. 0.39)%/min in non-smokers and 4.13 (1.06) %/min in smokers. These were about twice the clearance rates of B-DTPA, which in the corresponding groups were 0.41 (0.26) and 2.12 (0.72)%/min respectively. The ratio of the B-DTPA/DTPA clearance rates was, in all subjects, less than the ratio (0.74) of the cube roots of the molecular masses of the solutes, assumed to correspond to the ratio of their free diffusion coefficients in water, and was not significantly different between smokers and non-smokers. As alveolar permeability increased, the ratio of clearance rates in the entire population showed a significant trend to increase in a non-linear fashion towards the value corresponding to the ratio of the free diffusion coefficients. We conclude that the diffusion of at least the larger of these two solutes through the pulmonary alveolar epithelium is restricted (i.e. associated with a reflection coefficient greater than zero). Cigarette smoking, however, does not appear to cause a loss of this restriction, and may increase solute clearance by other mechanisms, such as reducing fluid volume within the alveolus, thereby raising the local radiotracer concentration, or increasing the number of pores available for solute exchange without affecting pore size. Conversely, if restriction was lost in lung disease, the ratio of the clearance rates of two solutes of dissimilar sizes could be used to detect disease in smokers as well as non-smokers.

A rapid method for PCR detection of bovine materials in animal feedstuffs

Rapid identification of bovine materials in animal feedstuffs is essential for effective control of a potential source of bovine spongiform encephalopathy. We have developed a rapid method for the detection of the presence of bovine materials in animal feeds. Animal feed samples were prepared by a Chelex-100 treatment method, then subjected to polymerase chain reaction (PCR) detection. The assay can be completed in 2 h including 30 min for sample preparation, 35-65 min for PCR cycling and 30 min for gel electrophoresis. This method is not only rapid, simple and consistent, but also avoids a hazardous waste disposal issue associated with a previously described guanidine thiocyanate (GuSCN) extraction-PCR method.

Clearance kinetics of solutes used to measure glomerular filtration rate

Agents used to measure glomerular filtration rate (GFR) give a biexponential plasma disappearance curve on multiple peripheral venous sampling between 20 min and 4 h after intravenous injection. These two exponentials are generally regarded to represent equilibration of agent throughout the extracellular fluid (ECF) space and renal clearance, respectively. In seven subjects undergoing diagnostic arteriography, arterial and antecubital venous plasma samples were obtained up to 60 min in five and up to 120 min in two following simultaneous intravenous injection of 99Tcm-diethylene triamine pentaacetate (99Tcm-DTPA) and inulin. The count rate from 99Tcm was simultaneously recorded over the calf with a collimated scintillation probe in five subjects up to 60 min post-injection. The arterial and venous time-concentration curves were interpolated and subtracted to give a curve of the arterio-venous (A-V) concentration difference, which was then integrated. Arterial time-concentration curves display three exponentials, the first of which has the largest amplitude and disappears by about 20 min. The A-V concentration difference becomes zero at about the same time. The integral of the A-V concentration difference, which represents activity in the interstitial space of the forearm, has a time course consistent with the second compartment of a model of two compartments in series (the first being plasma) and a time course that is reciprocally similar to the first exponential of the triexponential arterial plasma curve. The curve externally recorded by scintillation probe has a shape consistent with a signal that is the composite of interstitial 99Tcm-DTPA and plasma 99Tcm-DTPA activities. The arterial plasma clearance curve of GFR agents is triexponential; the first exponential reflects equilibration of agent between plasma and the interstitial space of carcass tissue (mainly muscle and skin). The second exponential is minor compared with the first; it is not clear what it represents. The third exponential reflects renal clearance.

Challenge differentially affects cytokine production and metabolic status of growing and finishing swine

Growing (35 kg body weight) and finishing (85 kg body weight) swine challenged with endotoxin (Escherichia coli O55:B5) at a dose of either 2 or 20 microg/kg produced tumor necrosis factor (TNF)alpha in a dose-response relationship as measured by bioassay. Peak TNFalpha plasma levels were observed 1-2 hr post-challenge, returning to basal values 4 hr post-challenge. However, both an enzyme-linked immunosorbent assay specific for swine TNFalpha and total human TNFalpha demonstrated no dose-response relationship; peak plasma levels of immunoreactive TNFalpha were also observed 1-2 hr post-challenge. Maximal plasma interleukin-6 levels occurred 1-2 hr post-challenge and remained elevated through 8 hr post-challenge; there was no effect of lipopolysaccharide dose or metabolic status. Although the metabolic status of the animals also affected glucose levels, with growing animals exhibiting greater sensitivity compared with finishing animals, endotoxin-induced decreases in blood glucose levels were primarily dose-dependent. In contrast, changes in plasma urea nitrogen and free fatty acid (FFA) levels were strictly related to the metabolic status. Urea nitrogen levels were unchanged in growing swine, whereas they were increased in finishing swine and remained elevated 24 hr post-challenge. FFA levels in growing and finishing swine increased 3-6 hr post-challenge. FFA levels returned to basal values for finishing swine 24 hr post challenge, but in growing swine remained elevated 24 hr post-challenge. Plasma aspartate transaminase levels were increased through 24 hr post-challenge; animals given a dose of 20 microg/kg exhibited the greatest increase. Similarly, swine challenged with a dose of 20 microg/kg also exhibited the greatest increase in levels of conjugated bilirubin; there was no effect on unconjugated (free) bilirubin. These results demonstrate that endotoxin challenge of swine result in a pattern of changes that are dependent on both the dose of endotoxin used and the metabolic status of the animal examined.

Appropriate corrections to glomerular filtration rate and volume of distribution based on the bolus injection and single-compartment technique

The bolus injection, single-compartment technique for measuring GFR overestimates the true value. Nevertheless, assuming that for a given indicator the area under the first exponential of the plasma clearance curve is constant from subject to subject, the observed (uncorrected) value can be corrected by multiplication with a 'sliding' factor, the value of which is a nonlinear function of GFR. Several second-order polynomials, based on pre-determined relationships between simultaneously determined two-compartment and one-compartment GFR, have been described for correcting GFR (GFR correction). It is, however, theoretically more rational to use a factor which depends on the rate constant, alpha2, of the terminal exponential of the clearance curve. We have therefore determined a set of linear equations from retrospectively analysed multiple-sample inulin, 99mTc-DTPA and 51Cr-EDTA clearance curves to enable correction of GFR using alpha2. A set of linear equations is also developed to correct the volume of distribution (Vd) of the indicator (close to extracellular fluid volume for these indicators), which is also overestimated by the one-compartment technique. At low levels of GFR, alpha2-corrected GFR is similar to uncorrected GFR for all three indicators. As GFR increases, however, uncorrected GFR progressively overestimates (alpha2-corrected GFR. The overestimation is greater for inulin than for 99mTc-DTPA or 51Cr-EDTA. In the one-compartment approximation, Vd is overestimated more than GFR, and again the greatest overestimation is seen with inulin. In a prospective study of 129 patients undergoing routine measurement of GFR with 51Cr-EDTA, alpha2 correction using a factor based on retrospective EDTA data gave values of GFR which were higher than values obtained from GFR correction using a previously published polynomial (also based on EDTA clearances) by 15% in children and 12.5% in adults when uncorrected GFR was 150 ml/min/1.73 m2. Moreover, the ratio of uncorrected GFR to GFR-corrected GFR was higher in children than adults. We conclude that alpha2 is a more rational variable with which to correct two-sample or three-sample GFR than GFR itself, that the correction formulae are not interchangeable between inulin on the one hand and EDTA and DTPA on the other, and that the relative magnitudes of the corrections given by alpha2 correction versus GFR correction are different for children and adults.

Bimodal granulocyte transit time through the human lung demonstrated by deconvolution analysis

The lungs are an important site of granulocyte pooling. The aim of the study is to quantify pulmonary vascular granulocyte transit time using deconvolution analysis, as has previously been performed to measure pulmonary red cell transit time. Granulocyte and red cell studies were performed in separate groups of patients. Both cell types were labelled with Tc-99m, which for granulocyte labelling was complexed with hexamethylpropyleneamine oxime (HMPAO). The red cell impulse response function (IRF) was monoexponential with a median transit time of 4.3 s. The granulocyte IRF was biexponential in 19 of 22 subjects, 18 of whom had systemic inflammation (inflammatory bowel disease, systemic vasculitis or graft-vs-host disease) and four were controls without inflammatory disease. The median transit time of the fast component ranged from 20 to 25 s and of the slow component 120-138 s in the four patient groups. The fraction of cells undergoing slow transit correlated significantly with (a) mean granulocyte transit time and (b) the fraction showing shape change in vitro. We conclude that granulocyte transit time through the pulmonary circulation is bimodal and that shape-changed (activated) cells transit more slowly that non-activated cells. The size of the fraction undergoing slow transit is closely related to mean granulocyte transit time and is an important determinant of the size of the pulmonary vascular granulocyte pool.

Bidirectional transport of iminodiacetic organic anion analogues between plasma and hepatocyte

The kinetics of organic anions are well described and back-diffusion from hepatocyte to plasma is accepted. Although iminodiacetic (IDA) analogues, as organic anions, should also show bidirectional transport between hepatocyte and plasma, this has not been directly demonstrated heretofore. The aim of this study was to directly demonstrate back-diffusion and to quantify it in terms of its fractional rate constant. Kinetics of diethyl IDA were studied in three anaesthetised dogs in which femoral arterial and hepatic venous samples were obtained after injection of tracer into (a) a peripheral vein or (b) hepatic artery or portal vein. Arterial time-concentration curves were also compared between peripheral venous and either hepatic arterial or portal venous injections. Time-activity curves were recorded from regions of interest over the cardiac blood pool and peripheral hepatic parenchyma in 30 patients undergoing routine IDA hepatobiliary imaging with diethyl IDA or mebrofenin and fractional rate constants of clearance of IDA from the hepatocyte compared between compartmental and deconvolution analyses. After peripheral injection in dogs, there was an early arteriovenous concentration gradient across the liver indicating an hepatocyte extraction fraction in the three animals of 0.9, 0.8 and 0.6. The net extraction fraction decreased exponentially over 40 min. Time-concentration curves from hepatic vein and femoral artery were virtually superimposed following intrahepatic injections. Peripheral arterial curves, however, had different shapes according to whether injections were intrahepatic or peripheral, and were consistent with significant back-diffusion. In clinical studies, the blood disappearance curves were fitted as the sum of two exponentials and the liver curves as the difference of two exponentials (with rate constants denoted alpha1h and alpha2h). Based on compartmental analysis of the blood curves, the sum of the fractional rate constants of tracer movement from hepatocyte to bile canaliculus (k32) and to plasma (k12) was similar to and correlated with the rate constant, alpha, of the hepatocyte impulse response function (r=0.62, n=30, P<0.001). In contrast, alpha1h and alpha2h were respectively clearly greater and smaller than alpha. Moreover, neither of these hepatic rate constants correlated with alpha. Diffusion of IDA from hepatocyte to blood is significant and even in the presence of normal liver function accounts for about 50% of IDA transport out of the hepatocyte. It should be taken into account in pharmacokinetic studies based on either compartmental or deconvolution analysis.

Appropriate background correction for DTPA aerosol clearance

Measurement of the clearance rate of inhaled aerosols of 99mTc-diethylenetriamine pentaacetic acid (DTPA) from distal airway to pulmonary capillary is a sensitive technique for the detection of lung injury. As the solute diffuses across the blood-gas barrier, the concentration in circulating blood increases, giving rise to a background signal superimposed on the signal from residual DTPA in the airway. Background subtraction is conventionally based on the thigh, but this tissue has the disadvantage in that its composition, in terms of the relative volumes of its extracellular extravascular and intravascular compartments (a ratio of approximately 4:1), is quite different from that of the lung (<1:6). With comparison to the thigh, we examined alternative regions for background, liver, and cranium, which have extravascular-to-intravascular compartment ratios much closer to these for the lung, to determine the most appropriate background for correction of the pulmonary signal. From 1 min after intravenous injection of 99mTc-DTPA, the time-activity curves recorded by a gamma camera over the liver and lung in a group of otherwise normal cigarette smokers decreased up to 30 min after injection, with time courses that could essentially be superimposed on each other; the curve recorded over the thigh with a separate scintillation probe continued to increase. The curve recorded over the cranium had a time course similar to that for the liver and lung. Following aerosol inhalation, the lung clearance rates over the initial 7 min when background subtraction was used, based on the liver, cranium, and thigh were, respectively, 4.9 +/- 2.9, 4.7 +/- 2. 6, and 5.4 +/- 3.4 (SD) %/min, compared with 4.1 +/- 2.2%/min without subtraction. The corresponding values based on 30 min of data were 3.3 +/- 1.4, 3.4 +/- 1.4, 4.2 +/- 2.3, and 2.8 +/- 1. 0%/min. When the liver was used for background, the lung clearance curves were clearly multiexponential, whereas thigh correction tended to give curves that were monoexponential or even convex upward on semilogarithmic axes. With an appropriate region for background, the true shape of a lung curve can be identified, which permits the study of an intervention on the clearance while it is in progress. The intravenous DTPA, required for calibrating the background regions, can be given before inhalation of the tracer.

Morphological conservation of limb natural pendular period in the domestic dog (Canis familiaris): implications for locomotor energetics

For better understanding of the links between limb morphology and the metabolic cost of locomotion, we have characterized the relationships between limb length and shape and other functionally important variables in the straightened forelimbs and hindlimbs of a sample of 12 domestic dogs (Canis familiaris). Intra-animal comparisons show that forelimbs and hindlimbs are very similar (not significantly different) in natural pendular period (NPP), center-of-mass, and radius of gyration, even though they differ distinctly in mass, length, moment-of-inertia, and other limb proportions. The conservation of limb NPP, despite pronounced dissimilarity in other limb characteristics, appears to be the result of systematic differences in shape, forelimbs tending to be cylindrical and hindlimbs conical. Estimating limb NPP for other species from data in the literature on segment inertia and total limb length, we present evidence that the similarity between forelimbs and hindlimbs in NPP is generally true for mammals across a large size range. Limbs swinging with or near their natural pendular periods will maximize within-limb pendular exchange of potential and kinetic energy. As all four limbs of moderate- and large-size animals swing with the same period during walking, maximal advantage can be derived from the pendular exchange of energy only if forelimbs and hindlimbs are very similar in NPP. We hypothesize that an important constraint in the evolution of limb length and shape is the locomotor economy derived from forelimbs and hindlimbs of similar natural pendular period.