Milk antimicrobial drug residue assay results in cattle with experimental, endotoxin-induced mastitis

Antimicrobial drug residue testing was performed on milk samples obtained from 8 cows with experimental endotoxin-induced mastitis, using 4 commercially available assay kits. Although none of the cows in the study received antimicrobials, only 1 of the 4 assay procedures, assay C, had consistently negative results (specificity = 1.00). The proportion of positive assay results varied from 0 to 1.00 among combinations of sampling time, sample status (endotoxin-infused quarter vs composite noninfused sample). The proportion of positive results found when assay C was used (0) differed significantly from the proportion found when the 3 other assays were used. The proportion of positive results did not differ significantly between assay A (0.45) and assay B (0.48); however, both assays had a significantly lower proportion of positive assays than did assay D (0.86). Logistic regression models were developed predicting positive milk antimicrobial drug residue assay results as a function of assay kit, sample status, and time interval following experimental challenge exposure. Using assay A as a baseline risk, assay B and assay D were more likely to have positive assay results, and assay C had a decreased risk of positive assay results. Milk samples from endotoxin-infused quarters were at increased risk for positive assay results, compared with noninfused composite samples. Samples collected from endotoxin-infused quarters or control quarters were at increased risk for positive assay results following the intramammary infusion of endotoxin. Our findings suggest that specificity of milk antimicrobial drug residue assays varies greatly among assay kits and that intramammary inflammation may increase the proportion of false-positive assay results.

Critical performance behaviors of radiology residents: evaluation of two category systems

OBJECTIVE

Previous research has suggested that certain behavioral aspects of job performance are critical for successful performance in a diagnostic radiology residency. We report two studies conducted to determine the long-term stability of critical performance behaviors for radiology residents and refine their definitions.

SUBJECTS AND METHODS

A trained psychology graduate student conducted critical incident interviews with 20 senior faculty in diagnostic radiology. From these interviews, the faculty generated 120 descriptions of exemplary or poor resident performance. These descriptors were then independently sorted by two radiologists into the previously defined categories of behaviors to evaluate consistency of the behaviors. As a second study, the 120 descriptors were sorted into an expanded behavioral definition system and the reproducibility, using the expanded system, was compared with the original results.

RESULTS

The interrater reliability for placing the current incidents in the originally described behavioral categories was good (Cohen's kappa 0.70). The overall distribution of incidents showed strong similarity to the original data. Sorting into the expanded categories improved the Cohen's kappa from 0.70 to 0.92, indicating that the expanded behavioral definitions improved reliability for categorizing a behavioral incident.

CONCLUSION

The critical behaviors necessary for successful performance in diagnostic radiology residency are stable over time. The expanded and refined system of definitions of these behaviors is more efficacious than the original system was.

Evaluation of a digital workstation for interpreting neonatal examinations. A receiver operating characteristic study

RATIONALE AND OBJECTIVES

The purpose of this study is to compare the diagnostic accuracy of interpreting clinical neonatal radiographs using a commercially available digital workstation versus conventional radiographic images.

METHODS

The case sample consists of 100 chest or abdominal radiographs from the neonatal intensive care unit in which diagnosis was confirmed. Four radiologists served as observers. During two initial reading sessions, half of the studies were viewed on digital radiography monitors and the other half by plain film. Observers indicated whether each patient had normal or abnormal findings and their degree of confidence in this judgment. Six weeks later, observers viewed cases on the alternate presentation system. Two statistical analyses were performed: the data from each observer were treated as a separate experiment in the first analysis; the data from all observers were combined using a new method in the second analysis.

RESULTS

No differences between areas under receiver operating characteristic (ROC) curves for viewing on the picture archiving and communication system (PACS) console and plain film were found for any observer (0.86 versus 0.86, 0.89 versus 0.86, 0.88 versus 0.85, 0.83 versus 0.82).

CONCLUSIONS

The study suggests that for pediatric plain film images, video images offer diagnostic information comparable with that of conventional radiographs for neonatal examinations.

Distribution and characterization of cyclooxygenase immunoreactivity in the ovine brain

Evidence from tissue culture studies suggests that glial cells are the principal source of prostaglandins in the brain. We have used immunohistochemistry, Western blot analysis, and enzyme activity assays to localize cyclooxygenase (COX), the enzyme responsible for the conversion of arachidonic acid to prostaglandins, in situ in the normal ovine brain. We observed very few immunoreactive glial cells. In contrast, an extensive distribution of COX-like immunoreactive (ir) neuronal cell bodies and dendrites and a corresponding pattern of COX enzyme activity were observed. COXir neurons were most abundant in forebrain sites involved in complex, integrative functions and autonomic regulation such as the cerebral cortex, hippocampus, amygdala, bed nucleus of the stria terminalis, substantia innominata, dorsomedial nucleus of the hypothalamus, and tuberomammillary nucleus. Moderate populations were observed in other regions of the central nervous system implicated in sensory afferent processing, including the dorsal column nuclei, spinal trigeminal nucleus, and superior colliculus, and in structures involved in autonomic regulation, such as the nucleus of the solitary tract, parabrachial nucleus, and the periaqueductal gray matter. We did not observe COXir axons or terminal fields, however. Our results suggest that neurons may use prostaglandins as intracellular or perhaps paracrine, but probably not synaptic, mediators in the normal brain.

Prostanoid biosynthesis and mechanisms of action

Prostanoids are local hormones formed from arachidonic acid that coordinate responses to circulating hormones which elicit prostanoid synthesis. For example, in the kidney, prostaglandin (PG) E2 synthesized by collecting tubule epithelia in response to arginine vasopressin (AVP) acts on the parent collecting tubule as well as the neighboring thick limb to modulate NaCl and water reabsorption occurring in response to AVP. Studies performed over the last 15 years have defined the major cellular and subcellular sites of PG synthesis in the kidney. In addition, it is now recognized that the multiple cellular actions of prostanoids in the kidney are mediated through receptors coupled to guanine nucleotide regulatory proteins. The goal of this review is to summarize recent biochemical and molecular biological studies on prostanoid biosynthetic enzymes and on prostanoid receptors. The major topics to be addressed are 1) phospholipid precursors of arachidonate, 2) membrane-associated and cytosolic phospholipase A2s, 3) PG endoperoxide (PGH) synthase isozymes, 4) thromboxane A (TxA) synthase, and 5) TxA/PGH and PGE receptors.

Prostaglandin endoperoxide synthase. The aspirin acetylation region

Aspirin selectively acetylates Ser-530 of prostaglandin endoperoxide (PGH) synthase-1. This causes inactivation of the cyclooxygenase activity of the enzyme, but does not appreciably affect its peroxidase activity. Although the aspirin-acetylated enzyme is inactive, we found that PGH synthase-1 in which Ser-530 had been replaced with an alanine was catalytically active; accordingly, we proposed that aspirin inhibits cyclooxygenase activity by placing a larger than normal side chain at position 530 thereby interfering with arachidonate binding (DeWitt, D.L., El-Harith, E. A., Kraemer, S. A., Andrews, M. J., Yao, E. F., Armstrong, R. L., and Smith, W. L. (1990) J. Biol. Chem. 265, 5192-5198). As a further test of this hypothesis we have used site-directed mutagenesis and transient expression in cos-1 cells to prepare and characterize five additional substitutions of Ser-530. Consistent with our proposal, the presence of amino acids with bulky side chains at position 530 inhibited cyclooxygenase activity and decreased the apparent affinity of the enzyme for arachidonate. In related work, we characterized a series of mutant PGH synthases-1 having substitutions at residues adjoining Ser-530, including Phe-529, Leu-531, Lys-532, and Gly-533, in order to evaluate the contributions of each residue to cyclooxygenase catalysis. The most significant conclusion of this part of the study is that residues 529-533 all are important for the peroxidase activity as well as the cyclooxygenase activity of PGH synthase-1. Phe-529, in particular, was found to be critical for PGH synthase-1 structure and catalysis; some substitutions at this position led to the production of proteins lacking about 100 amino acids from their COOH termini.

The predictive utility of behavior-based interviewing compared with traditional interviewing in the selection of radiology residents

RATIONALE AND OBJECTIVES

This study compares the predictive use of measures based on traditional faculty and resident interviews of residency applicants with measures obtained through behavior-based interviewing. A special emphasis was placed on predicting residents' noncognitive abilities.

METHODS

One hundred fifty-one resident applicants, over a 3-year period, were interviewed using standard interviews by faculty and residents. These residents also were interviewed with an experimental behavior-based accomplishment interview. Four years later, during their diagnostic radiology residency, evaluations of performance were gathered on these applicants from their residency director.

RESULTS

Results indicated that scores based on responses given during the accomplishment interviews added considerable predictive utility to the low prediction demonstrated by traditional interviews.

CONCLUSIONS

These findings imply that improving unstructured faculty and resident interviews to obtain, in a more rigorous manner, desired information about noncognitive abilities may be a key to successful resident selection.

AHR-9294: a novel inhibitor of H,K-ATPase antagonizes gastric HCl secretion in vivo

8-Methoxy-4-[(2-isopropylphenyl)amino]-3-quinolinecarboxylate ethyl ester (AHR-9294) inhibited acid secretion stimulated by histamine, pentagastrin or carbachol in rats, and by histamine or feeding in dogs. AHR-9294 was about half as potent as omeprazole and exhibited a shorter duration of action. Based on its inhibition of acid secretion induced by different secretagogues and its lack of effect on histamine-stimulated adenylate cyclase activity, AHR-9294 does not appear to operate at the histamine receptor or adenylate cyclase. Rather, studies on enriched oxyntic microsomal preparations showed AHR-9294 to be an effective inhibitor of the H+ pump enzyme, H,K-ATPase, suggesting this might be the site of antisecretory activity. Kinetic studies revealed that inhibition of both K(+)-activated ATPase and p-nitrophenylphosphatase by AHR-9294 was purely competitive with K+ and its congeners, indicating that AHR-9294 and its analogs belong to the class of compounds known as "K+)-site" inhibitors. On the other hand, inhibition by AHR-9294 was noncompetitive with both ATP and p-nitrophenylphosphatase on their respective rates of hydrolysis (i.e., both Vmax and the apparent Km were reduced, but Vmax/Km was unchanged). Studies on partial reactions of the H,K-ATPase showed that the rate of ATP/ADP exchange was unaffected by AHR-9294 and the steady-state level of phosphoenzyme was only partially reduced (thus ATP/enzyme interaction was not affected); however, the rate of K(+)-catalyzed dephosphorylation of phosphoenzyme was markedly decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

A lipoxygenase pathway of arachidonic acid metabolism mediates FMRFamide activation of a potassium current in an identified neuron of Helisoma

The neuropeptide FMRFamide causes a presynaptic inhibition of neurotransmitter release from neuron B5 of Helisoma. In this study we demonstrate that one of FMRFamide's actions is to activate an outwardly rectifying potassium current. Arachidonic acid also activates an outward current in B5. The phospholipase A2 inhibitor, 4-bromophenacylbromide (BPB), and nordihydroguaiaretic acid (NDGA), an inhibitor of arachidonic acid metabolism, but not indomethacin, block FMRFamide's activation of the potassium current. Taken together these data demonstrate that one of FMRFamide's presynaptic actions is to activate a potassium current through a lipoxygenase pathway of arachidonic acid metabolism.

Expression of prostaglandin endoperoxide synthase-1 in a baculovirus system

A cDNA coding for ovine prostaglandin endoperoxide (PGH) synthase-1 was used to construct a recombinant baculovirus which was expressed in Spodoptera frugiperda (Sf9) insect cells. Two proteins reactive with anti-PGH synthase antibody were produced. A larger protein (Mr = 72,000) coelectrophoresed with native enzyme; a smaller, more abundant protein (Mr = 66,000) was unglycosylated enzyme. About 90% of both the immunoreactivity and the cyclooxygenase activity were present in a low speed (10(5) g x min) pellet; variable but low peroxidase activities were observed in this fraction. The specific cyclooxygenase activity of solubilized PGH synthase-1 from Sf9 cells was 56 units/mg versus 112 units/mg for the same cDNA expressed in cos-1 cells. The baculovirus-insect cell system is not ideal for generating large amounts of active PGH synthase-1 apparently because of inefficient N-glycosylation.

Effectiveness of teaching radiologic image interpretation in gross anatomy. A long-term follow-up

This prospective study was designed to gauge the effectiveness of teaching radiologic interpretation during a gross anatomy course for first-year medical students by measuring short- and long-term ability to identify normal anatomic structures on radiologic diagnostic images. The evaluation required students to identify normal anatomic structures on radiographs, computed tomographs, ultrasonograms, and magnetic resonance images (MRIs). The assessments were made before (pre-test) and during (post-test) the experimental radiology portion of the gross anatomy course. The students were then retested 14 to 17 months later (long term). The pre-test correct response rate of 17% improved to 88% on the post-tests. After 14 to 17 months, the students had a 74% correct response rate on the same images and anatomic structures. This high level of long-term retention documents the effectiveness of integrating diagnostic radiologic imaging into normal gross anatomy instruction.

Activation of a peptidergic synapse locally modulates postsynaptic calcium influx

We examined the synaptic connection between Phe-Met-Arg-Phe-NH2 (FMRFamide)-immunoreactive neurone VD4 and its target neurone P1, both found in the central nervous system of the pond snail Helisoma trivolvis. The major FMRFamide-like peak in neurone VD4 appears to be FMRFamide itself, based on its high performance liquid chromatography (HPLC) elution time and immunoreactivity before and after oxidation, but small peaks are also present at the elution times of Phe-Leu-Arg-Phe-NH2 (FLRFamide) and Gly-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (GDPFLRFamide). The modulatory actions of the neuropeptides found in neurone VD4 were tested on the postsynaptic target cell P1. Bath application of both the tetrapeptides FMRFamide and FLRFamide at a concentration of 10(−5) mol l-1 reduced the macroscopic voltage-sensitive calcium current of neurone P1 in culture; FMRFamide by 45% and FLRFamide by 51%. Bath application of the heptapeptide GDPFLRFamide (10(−5) mol l-1) reduced the calcium current by only 8%. We reconstructed the synaptic connection between VD4 and P1 in culture. Action-potential-evoked calcium transients in neurites growing from P1 cells in culture were monitored using Fura-2. Addition of FMRFamide, FLRFamide or GDPFLRFamide reduced the magnitude of the calcium transient in P1. Stimulation of VD4 mimicked the effects of peptide application and caused localized reductions in the action-potential-evoked calcium transients in P1 at the points of contact between the neurites of neurones VD4 and P1. These results suggest that neurone VD4 modulates the calcium influx of neurone P1 through the release of endogenous FMRFamide-related peptides and that this modulatory action is restricted to sites of synaptic interaction.

Intramuscular desferrioxamine in patients with Alzheimer's disease

Although epidemiological and biochemical evidence suggests that aluminium may be associated with Alzheimer's disease (AD), there is no convincing proof of a causal link for aluminium in disease progression. We have completed a two year, single-blind study to investigate whether the progression of dementia could be slowed by the trivalent ion chelator, desferrioxamine. 48 patients with probable AD were randomly assigned to receive desferrioxamine (125 mg intramuscularly twice daily, 5 days per week, for 24 months), oral placebo (lecithin), or no treatment. No significant differences in baseline measures of intelligence, memory, or speech ability existed between groups. Activities of daily living were assessed and videorecorded at 6, 12, 18, and 24 month intervals. There were no differences in the rate of deterioration of patients receiving either placebo or no treatment. Desferrioxamine treatment led to significant reduction in the rate of decline of daily living skills as assessed by both group means (p = 0.03) and variances (p less than 0.04). The mean rate of decline was twice as rapid for the no-treatment group. Appetite (n = 4) and weight (n = 1) loss were the only reported side-effects. We conclude that sustained administration of desferrioxamine may slow the clinical progression of the dementia associated with AD.

Essential histidines of prostaglandin endoperoxide synthase. His-309 is involved in heme binding

Prostaglandin endoperoxide (PGH) synthase has a single iron protoporphyrin IX which is required for both the cyclooxygenase and peroxidase activities of the enzyme. At room temperature, the heme iron is coordinated at the axial position by an imidazole, and about 20% of the heme iron is coordinated at the distal position by an imidazole. We have used site-directed mutagenesis to investigate which histidine residues are involved in PGH synthase catalysis and heme binding. Individual mutant cDNAs for ovine PGH synthases were prepared with amino acid substitutions at each of 13 conserved histidines. cos-1 cells were transfected with each of these cDNAs, and the cyclooxygenase and peroxidase activities of the resulting microsomal PGH synthases were measured. Mutant PGH synthases in which His-207, His-309, or His-388 was replaced with either glutamine or alanine lacked both activities. Gln-386 and Ala-386 PGH synthase mutants exhibited cyclooxygenase but not peroxidase activities. Other mutants exhibited both activities at varying levels. Because binding of heme renders native PGh synthase resistant to cleavage by trypsin, we examined the effects of heme on the relative sensitivities of native, Ala-204, Ala-207, Ala-309, Ala-386, and Ala-388 mutant PGH synthases to trypsin as a measure of the heme-protein interaction. The Ala-309 PGh synthase mutant was notably hypersensitive to tryptic cleavage, even in the presence of exogenous heme; in contrast, the native enzyme and the other alanine mutants exhibited similar, lower sensitivities toward trypsin and, except for the Ala-386 mutant, were partially protected from trypsin cleavage by heme. Preincubation of the native and each of the alanine mutant PGH synthases, including the Ala-309 mutant, with indomethacin protected the proteins from trypsin cleavage. Thus, all the mutant proteins retain sufficient three-dimensional structure to bind cyclooxygenase inhibitors. Our results suggest that His-309 is one of the heme ligands, probably the axial ligand, of PGH synthase. Two other histidines, His-207 and His-388, are essential for both PGH synthase activities suggesting that either His-207 or His-388 can serve as the distal heme ligand; however, the trypsin cleavage measurements imply that neither His-207 nor His-388 is required for heme binding. This is consistent with the fact that only 20% of the distal coordination position of the heme iron of PGH synthase is occupied by an imidazole side chain.

Linear simultaneous solution for temperature and absorbing constituent profiles from radiance spectra

A linear form of the radiative transfer equation (RTE) is formulated for the direct and simultaneous estimation of temperature and absorbing constituent profiles (e.g., water vapor, ozone, methane) from observations of spectral radiances. This unique linear form of the RTE results from a definition for the deviation of the true gas concentration profiles from an initial specification in terms of the deviation of their effective temperature profiles from the true atmospheric temperature profile. The effective temperature profile for any absorbing constituent is that temperature profile which satisfies the observed radiance spectra under the assumption that the initial absorber concentration profile is correct. Differences between the effective temperature, derived for each absorbing constituent, and the true atmospheric temperature are proportional to the error of the initial specification of the gas concentration profiles. The gas concentration profiles are thus specified after inversion of the linearized RTE from the retrieved effective temperature profiles assuming that one of the assumed concentration profiles is known (e.g., CO(2)). Because the solution is linear and simultaneous, the solution is computationally efficient. This efficiency is important for dealing with radiance spectra containing several thousand radiance observations as obtained from current airborne and planned future spaceborne interferometer spectrometer sounders. Here the solution is applied to spectral radiance observations simulated for current filter radiometers and planned spectrometers to demonstrate the anticipated improvement in future satellite sounding performance as a result of improved instrumentation and associated sounding retrieval methodology.

Radiographic manifestations of anomalies of the brain

Congenital brain anomalies are classified as developmental anomalies, effects of teratogens, errors of histogenesis, or sequelae of infections. The imaging options for delineation of these anomalies are many; a basic understanding of the disorder is central to the effective choice of imaging modality. This review begins with a brief overview of embryogenesis then reviews the common congenital brain anomalies encountered in infants.

Analysis of the cost-effectiveness of PACS

Picture archiving and communications systems (PACS) have emerged as an important part of digital imaging technology. However, the future of PACS is uncertain because its economic viability is in doubt. Cost-effectiveness analysis is an accepted technique for evaluating the economics of new technologies. This paper addresses the cost-effectiveness of PACS and identifies factors that are important in determining the cost of PACS relative to film-based radiology. These include the impact of PACS on physician productivity, maintenance costs, discount rates, and the time period for amortization of capital goods. The effectiveness of PACS is also explored in terms of improvements in diagnostic accuracy and timely diagnosis. Financial and clinical impacts should be integrated to provide information about how PACS expenditures will affect radiology departments, hospitals, and national research and development objectives.

Large postnatally acquired porencephalic cysts: unexpected developmental outcomes

To determine the neurodevelopmental outcome for infants with posthemorrhagic intraparenchymal cysts, we reviewed retrospectively clinical, ultrasonographic, and developmental features in 16 affected children. At a mean follow-up age of 33 months, five subjects had normal cognitive outcomes (developmental quotient [DQ] or IQ greater than 83), nine had borderline to mild deficits (DQ or IQ, 52 to 83), but only three had moderate to severe deficits (DQ or IQ less than 52). Spastic cerebral palsy was present in 13 (81%); only one child (6%) had a chronic seizure disorder requiring medication. Cognitively normal children were less likely to have had neonatal seizures (P less than .05) and tended to have more localized cysts. Otherwise, we found no relationship between outcome and neonatal clinical or laboratory findings. Overall, these results suggest that although motor deficits are common in infants with severe intraventricular hemorrhage and porencephalic cysts, cognitive outcomes may be more favorable than has been suspected previously.