Biomedical subjects

S M Downs

Publications and source records attributed to S M Downs.

At least 19 recordsLinked to original sources

PubMed1999

Cost-effectiveness of transesophageal echocardiography to determine the duration of therapy for intravascular catheter-associated Staphylococcus aureus bacteremia.

BACKGROUND: The appropriate duration of therapy for catheter-associated Staphylococcus aureus bacteremia is controversial. Conventional practice dictates that all patients receive prolonged courses of intravenous antibiotics. Some clinicians recommend abbreviated therapeutic courses, but an alternate approach involves prospectively identifying patients for whom abbreviated therapy is appropriate. OBJECTIVE: To determine the cost-effectiveness of transesophageal echocardiography (TEE) in establishing duration of therapy for catheter-associated S. aureus bacteremia. DESIGN: Cost-effectiveness analysis. DATA SOURCES: MEDLINE search of literature; clinical data from patients with S. aureus bacteremia (n = 196) and patients with endocarditis (n = 60); and costs obtained from the study institution, regional home health agency, and national estimates of professional and technical fees. TARGET POPULATION: Patients with catheter-associated S. aureus bacteremia on native heart valves without intravenous drug use or clinically apparent metastatic infection, immunosuppression, or indwelling prosthetic devices. TIME HORIZON: Patient lifetime. PERSPECTIVE: Societal. INTERVENTIONS: Antibiotic treatment based on TEE results compared with 2- or 4-week empirical therapy. OUTCOME MEASURES: Quality-adjusted life expectancy, costs, and incremental cost-effectiveness ratios. RESULTS OF BASE-CASE ANALYSIS: Compared with empirical short-course therapy, the TEE strategy cost $4938 per quality-adjusted life-year (QALY) gained. The effectiveness of the TEE strategy and the effectiveness of the long-course strategy were sufficiently similar that the additional cost of empirical long-course therapy ($1,667,971 per QALY) was higher than that which society usually considers cost-effective. RESULTS OF SENSITIVITY ANALYSES: In a four-way sensitivity analysis (endocarditis prevalence, TEE cost, short-course relapse rate, and TEE specificity), compared with empirical short-course therapy, the TEE strategy results ranged from cost savings to $155,624 per QALY. CONCLUSION: Within the limitations of existing empirical data, this study suggests that for patients with clinically uncomplicated catheter-associated S. aureus bacteremia, the use of TEE to determine therapy duration is a cost-effective alternative to 2- or 4-week empirical therapy.

Anti-Bacterial Agents↗

PubMed1999

Uptake and metabolism of adenosine mediate a meiosis-arresting action on mouse oocytes.

This study was carried out to evaluate the possible role of adenosine uptake and metabolism in mediating the inhibitory actions of this nucleoside on spontaneous mouse oocyte maturation. Uridine blocked 3H-adenosine uptake by oocyte-cumulus cell complexes (OCCs) and cumulus cell-enclosed oocytes (CEOs) by 82-85%, whereas uptake by denuded oocytes (DOs) was suppressed by 97%. Uridine had no effect on germinal vesicle breakdown (GVB) in CEOs when meiotic arrest was maintained with hypoxanthine or hypoxanthine plus adenosine but reversed the combined inhibitory action of these purines in DOs. Five of six adenosine analogs that bind to purinoceptors demonstrated meiosis-arresting activity but not in relation to their relative affinities for inhibitory or stimulatory adenosine receptors and only at high concentrations. Moreover, in DOs, uridine reversed the inhibitory effect of 2-chloroadenosine and 5'-N-ethylcarboxamidoadenosine, two receptor agonists that are poor substrates for adenosine-metabolizing enzymes. Results of experiments with adenosine kinase inhibitors showed that methylmercaptopurine riboside (MMPR) and tubercidin, but not 5'-amino-5'-deoxyadenosine, reversed meiotic arrest maintained by hypoxanthine +/- adenosine, but this required an additional inhibitory action on de novo purine synthesis. Inhibition of de novo purine synthesis alone was not sufficient because azaserine failed to reverse meiotic arrest. MMPR was a very potent meiosis-inducing agent, completely reversing meiotic arrest in CEOs and DOs in the presence of a variety of meiotic inhibitors. The adenosine deaminase inhibitor deoxycoformycin had opposite effects on oocyte maturation depending on the presence or absence of adenosine: the inhibitory action of hypoxanthine alone was bolstered, but the meiosis-arresting action of adenosine was reversed. These data therefore indicate that at low adenosine concentrations phosphorylation predominates, but at higher adenosine concentrations deaminated products contribute to the meiotic inhibition. This idea was borne out by the ability of inosine to mimic the synergistic interaction of adenosine with hypoxanthine. The action of adenosine is not due to deamination to inosine and conversion to nucleotides through the hypoxanthine salvage pathway because adenosine-mediated inhibition was not compromised in oocytes from mutant mice unable to salvage hypoxanthine.

Adenosine↗

PubMed1999

Metabolism of radiolabeled glucose by mouse oocytes and oocyte-cumulus cell complexes.

This study was carried out to examine the metabolism of [1-14C]-, [6-14C]-, and [5-3H]glucose by oocyte-cumulus cell complexes (OCC) and denuded oocytes (DO) and to test the hypothesis that metabolism of glucose through the pentose phosphate pathway is associated with meiotic induction. OCC or DO were cultured in hanging drops suspended from the cap of a microfuge tube, with NaOH serving as a trap to collect released 3H2O or 14CO2. Preliminary experiments established that this culture system supports both spontaneous and ligand-induced meiotic maturation. An initial time course experiment (1.5-6 h) showed that hypoxanthine-treated OCC from eCG-primed animals metabolized glucose principally via glycolysis, with an increase to 2.7-fold in response to FSH. Though more [1-14C]glucose was oxidized than [6-14C]glucose, its metabolism was about two orders of magnitude less than that of [5-3H]glucose. Also, FSH significantly increased oxidation of [1-14C]glucose but not [6-14C]glucose, indicating a preferential activation of the pentose phosphate pathway. Pyrroline carboxylate, an activator of the pentose phosphate pathway, increased the activity of this pathway to over 2-fold but failed to affect glucose oxidation through the tricarboxylic acid cycle. Glycolytic metabolism was increased by 25%. The addition of pyruvate to pyruvate-free medium resulted in significant reduction in the metabolism of all three glucose analogues. In OCC retrieved from hCG-injected, primed mice and cultured under hormone-free conditions, metabolic responses were similar to those in FSH-treated complexes cultured in hypoxanthine. DO metabolized glucose, but at a much reduced rate when compared to OCC. Pyruvate reduced the consumption of all three glucose analogues by DO. Pyrroline carboxylate reduced [5-3H]glucose metabolism by DO but had little effect on [1-14C]- and [6-14C]glucose oxidation. These data demonstrate metabolism of glucose by both DO and OCC, but reveal that cumulus cells are more active than the oocyte in this regard. In addition, induction of maturation by FSH, hCG, or pyrroline carboxylate was accompanied by a significant increase in the oxidation of [1-14C]glucose but not [6-14C]glucose by OCC, supporting a proposed role for the pentose phosphate pathway in meiotic induction.

Animals↗

PubMed1999

Technical report: urinary tract infections in febrile infants and young children. The Urinary Tract Subcommittee of the American Academy of Pediatrics Committee on Quality Improvement.

OVERVIEW: The Urinary Tract Subcommittee of the American Academy of Pediatrics Committee on Quality Improvement has analyzed alternative strategies for the diagnosis and management of urinary tract infection (UTI) in children. The target population is limited to children between 2 months and 2 years of age who are examined because of fever without an obvious cause. Diagnosis and management of UTI in this group are especially challenging for these three reasons: 1) the manifestation of UTI tends to be nonspecific, and cases may be missed easily; 2) clean voided midstream urine specimens rarely can be obtained, leaving only urine collection methods that are invasive (transurethral catheterization or bladder tap) or result in nonspecific test results (bag urine); and 3) a substantial number of infants with UTI also may have structural or functional abnormalities of the urinary tract that put them at risk for ongoing renal damage, hypertension, and end-stage renal disease (ESRD). METHODS: To examine alternative management strategies for UTI in infants, a conceptual model of the steps in diagnosis and management of UTI was developed. The model was expanded into a decision tree. Probabilities for branch points in the decision tree were obtained by review of the literature on childhood UTI. Data were extracted on standardized forms. Cost data were obtained by literature review and from hospital billing data. The data were collated into evidence tables. Analysis of the decision tree was used to produce risk tables and incremental cost-effectiveness ratios for alternative strategies. RESULTS: Based on the results of this analysis and, when necessary, consensus opinion, the Committee developed recommendations for the management of UTI in this population. This document provides the evidence the Subcommittee used in the development of its recommendations. CONCLUSIONS: The Subcommittee agreed that the objective of the practice parameter would be to minimize the risk of chronic renal damage within reasonable economic constraints. Steps involved in achieving these objectives are: 1) identifying UTI; 2) short-term treatment of UTI; and 3) evaluation for urinary tract abnormalities.

Child, Preschool↗

PubMed1998

Precursors of the purine backbone augment the inhibitory action of hypoxanthine and dibutyryl cAMP on mouse oocyte maturation.

In this study we have tested the hypothesis that precursors of the purine base backbone--glutamine, glycine, aspartic acid, and formate--promote meiotic arrest when included in medium containing established meiotic inhibitors and that this occurs in glucose-dependent fashion. An initial experiment established that in medium supplemented with 4 mM hypoxanthine and containing no purine precursors, very little meiotic arrest was maintained in cumulus cell-enclosed oocytes after 17-18 hr (90% germinal vesicle breakdown; GVB). Increasing concentrations of glucose reduced the maturation percentage such that only 57% had matured at 0.55 mM. The addition of 2 mM glutamine (Gln) alone reduced the maturation percentage in the absence of glucose (70% GVB), and the further addition of glucose revealed an additive inhibitory effect between these two supplements. Dose response experiments with Gln, glycine (Gly), aspartic acid and formate showed that in medium supplemented with hypoxanthine, very little inhibitory action was observed in the absence of glucose but that upon addition of this hexose, a dramatic decrease in maturation percentage was observed in the Gln and Gly groups. Results of experiments using combinations of precursors showed that when Gln and Gly were added together, greater augmentation of meiotic arrest maintained by either hypoxanthine or dibutyryl cAMP was achieved in the presence of glucose than with either amino acid alone. The addition of purine precursors significantly increased the extent of purine nucleotide production by oocyte-cumulus cell complexes, and this was accentuated by glucose. It is concluded that the presence of purine precursors can augment the meiosis-arresting action of established meiotic inhibitors in glucose-dependent fashion, and that this is due, at least in part, to their incorporation into purine nucleotides via the de novo synthetic pathway.

Animals↗

PubMed1998

Cost-effectiveness analysis of lead poisoning screening strategies following the 1997 guidelines of the Centers for Disease Control and Prevention.

OBJECTIVE: To compare blood lead (BPb) poisoning screening strategies in light of the 1997 recommendations by the Centers for Disease Control and Prevention, Atlanta, Ga. DESIGN: Cost-effectiveness analysis from the perspective of the health care system to compare the following 4 screening strategies: (1) universal screening of venous BPb levels; (2) universal screening of capillary BPb levels; (3) targeted screening of venous BPb levels for those at risk; and (4) targeted screening of capillary BPb levels for those at risk. Costs of follow-up testing and treatment were included in the model. RESULTS: Only universal venous screening detected all BPb levels of at least 0.48 micromol/L (10 microg/dL). Universal capillary screening detected between 93.2% and 95.5% of cases, depending on the prevalence of elevated BPb levels. Targeted screening was the least sensitive strategy for detecting cases. Venous testing identified between 77.3% and 77.9% of cases, and capillary testing detected between 72.7% and 72.8% of cases. In high-prevalence populations, universal venous screening minimized the cost per case ($490). In low- and medium-prevalence populations, targeted screening using venous testing minimized the cost per case ($729 and $556, respectively). In all populations, regardless of screening strategy, venous testing resulted in a lower cost per case than capillary testing. Sensitivity analyses of all parameters in this model demonstrated that this conclusion is robust. CONCLUSIONS: Universal screening detects all cases of lead poisoning and is the most cost-effective strategy in high-prevalence populations. In populations with lower prevalence, the cost per case detected using targeted screening is less than that of universal screening. The benefit of detecting a greater number of cases using universal screening must be weighed against the extra cost of screening. Regardless of whether a strategy of universal or targeted screening is used, the cost per case using venous testing is less than that of capillary testing.

Capillaries↗

PubMed1998

Effect of telemedicine on health outcomes in 87 infants requiring neonatal intensive care.

OBJECTIVE: This is an evaluation of a telemedicine system for the rapid interpretation of neonatal echocardiograms from a regional, level III neonatal intensive care unit (NICU). The use of telemedicine to support the cardiology needs of NICUs is increasing. However, there is very little published objective information regarding health outcomes or costs resulting from such telemedicine systems. The primary hypothesis tested was that the utilization of a telemedicine system for the interpretation of neonatal echocardiograms reduces the intensive care length of stay of low birthweight (LBW) infants. STUDY DESIGN: All infants who were admitted to neonatal intensive care at New Hanover Regional Medical Center during the first six months of the system were studied by the use of echocardiograms. They were compared with infants who were born in the same period of the previous year. The outcome measures were the intensive care length of stay, rate of transfer to academic medical centers, and mortality rate. RESULTS: A statistically non-significant reduction of 5.4 days in the intensive care length of stay (LOS) of low birthweight infants was observed (p = 0.37). The cost per echocardiogram transmitted was calculated at $33 compared to previous method of sending videotapes via overnight courier. CONCLUSIONS: While the sample size was inadequate to demonstrate improvements in health outcomes, the magnitude of the change and the low costs of the system suggest that this intervention is practical for obtaining rapid diagnostic and treatment support. Larger studies are warranted to confirm these findings and determine whether faster diagnosis and earlier initiation of treatment improve health outcomes of newborn infants.

Academic Medical Centers↗

PubMed1998

Meiotic induction in cumulus cell-enclosed mouse oocytes: involvement of the pentose phosphate pathway.

In this study we tested the hypothesis that the pentose phosphate pathway (PPP) participates in the meiotic induction of mouse oocytes. The electron acceptors methylene blue, phenazine ethosulfate (PES), and pyrroline-5-carboxylate (P5C) oxidize NADPH to NADP and activate the NADP-dependent enzymes of the PPP. Each of these compounds triggered a dose-dependent increase in meiotic maturation in hypoxanthine-arrested cumulus cell-enclosed oocytes during 17- to 18-h cultures. More than 96% of the oocytes underwent germinal vesicle breakdown (GVB) at the highest concentrations of P5C and PES tested (250 and 1 microM, respectively) as compared to only 45-52% of control oocytes. P5C was also stimulatory to denuded oocytes. Analysis of energy substrates in microdrop cultures revealed a 3.6-fold increase in glucose consumption by PES-treated oocyte-cumulus cell complexes that was associated with stimulation of GVB. On the other hand, 2-deoxyglucose, which interferes with glucose utilization, prevented the induction of maturation brought about by P5C. Apocynin and diphenyleneiodonium, inhibitors of NADPH oxidase, prevented meiotic maturation in the presence or absence of FSH. Gonadotropin-induced maturation was also prevented by 6-aminonicotinamide (6-AN) and dehydroepiandrosterone (DHEA), inhibitors of the two NADP-dependent enzymes of the PPP, and this was accompanied by suppression of glucose consumption. Phosphoribosyl-pyrophosphate (PRPP) is an important compound required in purine metabolism and can be formed from the end product of the oxidative arm of the PPP, ribose-5-phosphate. Ribose, which can be metabolized to PRPP, increased PRPP synthesis in complexes and induced meiotic maturation when added to hypoxanthine-arrested cumulus cell-enclosed oocytes in glucose-free medium in both the presence and absence of FSH. PRPP levels within complexes were also increased by glucose and FSH, but were reduced by hypoxanthine, 6-AN, and DHEA. In addition, exogenous PRPP stimulated maturation in hypoxanthine-arrested oocytes. These results support the proposition that glucose metabolism through the PPP is important in the meiotic induction mechanism and may involve the generation of PRPP that acts, at least in part, through the purine metabolizing pathways.

Animals↗

PubMed1997

Involvement of purine nucleotide synthetic pathways in gonadotropin-induced meiotic maturation in mouse cumulus cell-enclosed oocytes.

This study was carried out to test the hypothesis that purine nucleotide-generating pathways are required for ligand-stimulated oocyte maturation in meiotically arrested cumulus cell-enclosed oocytes. Oocytes from hormonally primed, immature mice were cultured overnight in Eagle's minimum essential medium containing dibutyryl cyclic AMP (dbcAMP) (to maintain meiotic arrest), plus either mycophenolic acid or alanosine (inhibitors of guanyl and adenyl nucleotide production, respectively). Follicle-stimulating hormone (FSH) was added either at the outset of culture or after a 3-hr preincubation period. Under either of these conditions, the inhibitors suppressed FSH induction of germinal vesicle breakdown (GVB). In addition, the potency of FSH as an inducer of GVB was reduced following the 3-hr preincubation period, but this could be prevented if nucleotide precursors such as hypoxanthine, guanosine, or adenosine were included during the first 3 hr. Furthermore, preincubation had little effect on FSH induction of GVB when hypoxanthine was used to maintain meiotic arrest for the entire culture period. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, could not mimic this protective effect of hypoxanthine. Azaserine and aminopterin, inhibitors of purine de novo synthesis, blocked hormone-triggered maturation in dbcAMP-arrested oocytes, but had little effect on hypoxanthine-arrested oocytes. The effect of azaserine on dbcAMP-treated oocytes could be reversed by the inclusion of AICA riboside, a compound that can be taken up by cells and phosphorylated to form AICAR, which can enter the purine de novo pathway at a point distal to the sites of azaserine inhibition. FSH was stimulatory to purine de novo synthesis, while azaserine, aminopterin, hypoxanthine, and AICA riboside all suppressed de novo synthesis in the presence or absence of FSH, with dbcAMP having no effect. HPLC analysis of 14C-hypoxanthine metabolism in oocyte-cumulus cell complexes revealed that changes in the pattern of purine metabolism did not mediate the meiosis-inducing effect of FSH. These data support the conclusion that purine nucleotide-generating pathways are vital participants in the mechanism(s) regulating hormone-induced meiotic maturation, and that either the de novo or salvage pathway can fulfill this nucleotide requirement.

Aminoimidazole Carboxamide↗

PubMed1997

Culture conditions affect meiotic regulation in cumulus cell-enclosed mouse oocytes.

To test the hypothesis that culture conditions influence meiotic regulation in mouse oocytes, we have examined the effects of six culture media, four organic buffers, and pH on spontaneous maturation, the maintenance of meiotic arrest and ligand-induced maturation in cumulus cell-enclosed oocytes from hormonally primed immature mice. The media tested were Eagle's minimum essential medium (MEM), Ham's F-10 (F-10), M199, M16, Waymouth's MB 752/1 (MB 752/1), and Leibovitz's L-15 (L-15). All six media supported > or = 94% spontaneous germinal vesicle breakdown (GVB) during a 17-18 hr incubation period, but polar body formation was lower in M199 and MB 752/1 than in the other media. The incidence of polar bodies could be increased in these two media by the addition of pyruvate. With the exception of M16 and MB 752/1, 4 mM hypoxanthine maintained a significant number of cumulus cell-enclosed oocytes in meiotic arrest. Inhibition could be restored by the addition of glutamine to M16 and pyruvate to MB 752/1. Follicle-stimulating hormone (FSH) and epidermal growth factor (EGF) stimulated GVB in those media in which hypoxanthine was inhibitory. dbcAMP was able to maintain meiotic arrest in all of the media, but was least effective in M16. FSH stimulated GVB in all dbcAMP-arrested groups except L-15, and FSH became stimulatory in L-15 when the pyruvate level was reduced to 0.23 mM and galactose was replaced with 5.5 mM glucose. When MEM was buffered principally with the organic buffers MOPS, HEPES, DIPSO, or PIPES (at 20 mM), high frequencies of GVB and polar body formation were observed in inhibitor-free medium. dbcAMP suppressed GVB in all groups; hypoxanthine also maintained meiotic arrest in all buffering conditions, although this effect was nominal in PIPES-buffered medium. FSH and EGF stimulated GVB in all dbcAMP- and hypoxanthine-treated groups. When the concentration of HEPES was increased from 20 mM to 25 mM, a more pronounced suppressive effect on maturation in both dbcAMP- and hypoxanthine-supplemented groups was observed in the absence of FSH. But whereas HEPES reduced the induction of maturation by FSH in dbcAMP-arrested oocytes, this buffer had no effect on FSH action in hypoxanthine-treated oocytes. When MEM was buffered with HEPES and the pH was adjusted to 6.8, 7.0, 7.2, or 7.4, a dramatic effect of pH on meiotic maturation was observed. pH had no significant effect on hypoxanthine salvage by oocyte-cumulus cell complexes, but FSH-induced de novo purine synthesis was significantly augmented by increased pH, in parallel with increased induction of GVB. The results of this study demonstrate that the use of different culture media, or minor changes in culture conditions, can lead to significant variation in (1) the spontaneous maturation of oocytes, (2) the ability of meiotic inhibitors to suppress GVB, or (3) the efficacy of meiosis-inducing ligands. Furthermore, such observations provide a unique opportunity to examine specific molecules and metabolic pathways that can account for this variation and thereby gain valuable insights into the mechanisms involved in meiotic regulation.

Animals↗

PubMed1997

Uptake and salvage of hypoxanthine mediates developmental arrest in preimplantation mouse embryos.

Preimplantation mouse embryos become arrested after first or second cleavage when cultured in hypoxanthine-supplemented Whitten's medium. We present evidence that the hypoxanthine-induced arrest is dependent on uptake and salvage of hypoxanthine and depletion of phosphoribosylpyrophosphate (PRPP) levels. Hypoxanthine uptake increased during the 2-cell stage and was augmented by glucose. HPLC analysis of [14C]hypoxanthine metabolism revealed that hypoxanthine was salvaged and converted to ATP and guanosine triphosphate (GTP), with a shift to more guanyl nucleotide production at the 3- to 4-cell stage. In embryos from mice with a null mutation for the salvage enzyme hypoxanthine-guanine phosphoribosyltransferase, hypoxanthine did not block development nor was it taken up by the embryos. Glucose, which is required for the hypoxanthine-induced arrest, produced a 5.3-fold increase in PRPP levels at the 2-cell stage, which was eliminated by hypoxanthine. We conclude that metabolism of hypoxanthine to nucleotides mediates its inhibitory action on preimplantation mouse embryos via negative feedback on PRPP synthetase, ultimately resulting in decreased PRPP availability and arrest of other PRPP-dependent pathways. Finally, reversal of the block by EDTA and cAMP-elevating agents may be mediated by alterations in hypoxanthine or glucose uptake, or by changes in the relative metabolism of hypoxanthine.

1-Methyl-3-isobutylxanthine↗

PubMed1997

Hypoxanthine regulation of oocyte maturation in the mouse: insights using hypoxanthine phosphoribosyltransferase-deficient animals.

In this study the effects of hypoxanthine (HX) on meiotic maturation were compared using oocytes from mice possessing a hypoxanthine phosphoribosyltransferase null mutation (HPRT-) and from the corresponding HPRT-competent background strain (HPRT+). Oocyte-cumulus cell complexes and cumulus cell-enclosed oocytes (oocytes cultured while enclosed by cumulus cells) from HPRT+, but not HPRT-, mice took up HX and contained significant levels of HPRT activity. In addition, FSH increased, and HX suppressed, the de novo synthesis of purines in HPRT+ complexes, whereas de novo synthesis was elevated in HPRT complexes and was unaffected by FSH or HX. After 3 h of HX treatment, lower frequencies of germinal vesicle breakdown (GVB) were observed in cumulus cell-enclosed than in denuded HPRT+ oocytes; however, identical frequencies of maturation were observed in denuded and cumulus cell-enclosed HPRT oocytes. This demonstrates a direct inhibitory action of HX on the oocyte that does not depend on salvage, plus an additional action of the cumulus cells that requires HPRT activity. Nevertheless, cumulus cells from HPRT- mice are capable of exerting an additional inhibitory action of dibutyryl cAMP (dbcAMP) on the oocyte. A kinetics analysis of FSH action on HX-arrested cumulus cell-enclosed HPRT+ and HPRT- oocytes revealed, first, that the inhibitory effect of the cumulus cells is transient and, second, that HPRT activity is not required for FSH induction of GVB in HX-arrested oocytes. When dbcAMP- or HX-arrested oocytes were treated with FSH, GVB was blocked to the same extent in HPRT- oocytes with the purine de novo synthesis inhibitor, azaserine, but this drug was less effective in HX-treated HPRT+ oocytes. These results confirm the importance of the de novo pathway in hormone-induced maturation and also support a role for purine salvage as an alternative source of nucleotide in this process.

Animals↗

PubMed1997

Substrate utilization and maturation of cumulus cell-enclosed mouse oocytes: evidence that pyruvate oxidation does not mediate meiotic induction.

This study was performed to address the possible role of pyruvate in meiotic induction in mouse oocytes. Cumulus cell-enclosed oocytes from primed, immature mice were cultured in 7.5 microliters microdrops under oil for 9 or 18 h in medium containing 4 mmol hypoxanthine l-1 plus 0.23 mmol pyruvate l-1, 1 mmol pyruvate l-1, or 1 mmol pyruvate l-1 plus 5.5 mmol glucose l-1. When compared with cultures containing 0.23 mmol pyruvate l-1, 1 mmol pyruvate l-1 induced germinal vesicle breakdown, and this was preceded by an increase in pyruvate utilization. Addition of glucose prevented both the increase in pyruvate consumption and the meiotic induction. When different combinations of pyruvate and glucose were tested on oocyte maturation in microdrop cultures, a high concentration of pyruvate or glucose alone was stimulatory to maturation. Addition of the complementary energy substrate prevented the induction of germinal vesicle breakdown and reduced the amount of substrate consumption. During spontaneous maturation in vitro, oocyte-cumulus cell complexes consumed glucose for the first 3 h; however, during the second 3 h period, which followed germinal vesicle breakdown, glucose consumption decreased and net pyruvate utilization was initiated. Treatment of hypoxanthine-arrested oocytes with dichloroacetate, an activator of pyruvate dehydrogenase, stimulated pyruvate consumption but had no effect on germinal vesicle breakdown. Although FSH stimulates meiotic resumption, no changes in pyruvate consumption were observed in response to this gonadotrophin. Measurement of oxygen consumption by hypoxanthine-treated complexes revealed no effect of high concentrations of pyruvate on respiration, and FSH treatment resulted in a suppression of oxygen utilization. These data indicate that, in mouse oocyte-cumulus cell complexes, pyruvate and glucose can each modulate metabolism of the other substrate, and the can significantly influence meiotic maturation of the oocyte. In addition, augmentation of pyruvate oxidation does not appear to play a mediating role in meiotic induction triggered by energy substrate manipulation or gonadotrophin treatment.

Animals↗

PubMed1997

Pediatric injury prevention counseling priorities.

OBJECTIVE: Child health care providers have a unique opportunity to conduct injury prevention counseling but limited empirical evidence for choosing prevention strategies. Efficient use of time requires that prevention strategies of higher priority be discussed before lower priority strategies. Our aim was to assess consensus among experts about the prioritization of prevention strategies for office based injury prevention counseling for parents of children under age two. DESIGN: We used a modified Delphi technique with 23 childhood injury prevention experts nationwide. Participants were blinded to the identities of each other. MEASURES: The first questionnaire, distributed via facsimile transmission, consisted of open ended questions about prevention strategies participants believe should be included and their prioritization methods. The second questionnaire was closed ended and based on the results of the first. RESULTS: Seventeen injury problems and 21 prevention strategies were suggested for counseling. Participants emphasized environmental strategies over more active, educational ones. Motor vehicle occupant injuries and car seats were given high priority scores by all participants. Smoke detectors, lowering the hot water heater temperature, and pool fencing also received high priority ratings. Participants based their decisions on the severity of the injury, the frequency with which the injury occured, and the availability of environmental strategies. However, they disagreed about the relative importance of these factors. Time constraints and parents' inability to absorb information led them to suggest limiting, to fewer than four, the number of prevention strategies addressed at any one visit. CONCLUSIONS: This study illustrates areas of consensus as well as unresolved dilemmas about pediatric injury prevention counseling. A rational decision making approach to prioritizing elements of clinical counseling is needed. Meanwhile, clinicians can use the findings of this study to derive their own judgments.

Accident Prevention↗

PubMed1997

A decision analytic method for scoring performance on computer-based patient simulations.

As computer based clinical case simulations become increasingly popular for training and evaluating clinicians, approaches are needed to evaluate a trainee's or examinee's solution of the simulated cases. We developed a decision analytic approach to scoring performance on computerized patient case simulations. We developed decision models for computerized patient case simulations in four specific domains in the field of infectious disease. The decision models were represented as influence diagrams. A single decision node represents the possible diagnoses the user may make. One chance node represents a probability distribution over the set of competing diagnoses in the simulations. The value node contains the utilities associated with all possible combinations of diagnosis and disease. All relevant data that the user may request from the simulation are represented as chance nodes with arcs to or from the diagnosis node and/or each other. Probabilities in the decision model were derived from the literature, where available, or expert opinion. Utilities were assessed by standard gamble from clinical experts. The process of solving computer based patient simulations involves repeated cycles of requesting data (history, physical examination or laboratory) and receiving these data from the simulations. Each time the user requests clinical data from the simulation, the influence diagram is evaluated with and without an arc from the corresponding chance node to the decision node. The difference in expected utility between the two solutions of the influence diagram represents the expected value of information (VOI) from the requested clinical datum. The ratio of the expected VOI from the data requested and the expected value of perfect information about the diagnosis is a normative measure of the quality of each of the user's data requests. This approach provides a continuous measure of the quality of the user's data requests in a way that is sensitive to the previous data collected. The score distinguishes serious from minor misdiagnoses. And the same influence diagram can be used to evaluate performance on multiple simulations in the same clinical domain.

Computer Simulation↗

PubMed1996

Glucose utilization during gonadotropin-induced meiotic maturation in cumulus cell-enclosed mouse oocytes.

Earlier work from this laboratory has determined that glucose plays an important role in the mechanisms regulating meiotic maturation in mammalian oocytes. In the current study, we have further explored the role of glucose in hormone-induced germinal vesicle breakdown (GVB) in an effort to better understand how glucose utilization and metabolism relate to the control of meiotic maturation in mouse cumulus cell-enclosed oocytes (CEO). When CEO were cultured in medium containing 4 mM hypoxanthine (to maintain meiotic arrest), 5.5 mM glucose, and 0.23 mM pyruvate, follicle-stimulating hormone (FSH) stimulated lactate accumulation in a time-dependent manner. Addition of 2-deoxyglucose (2-DG) to the medium at various times after the initiation of culture resulted in rapid termination of lactate production and suppression of FSH-induced GVB scored after 18 hr of culture, the effectiveness diminishing the longer the delay before addition of 2-DG. By 8 hr, addition of 2-DG was without effect on GVB. Similar effects were seen when FSH-treated CEO were washed free of glucose. In a 2-DG dose-response experiment, gonadotropin-induced lactate production was prevented, but this inhibition did not necessarily prevent GVB. The activities of six metabolic enzymes were measured in extracts of freshly isolated complexes, and in order of increasing activity were: hexokinase, 6-phosphogluconate dehydrogenase, glucose-6-phosphate dehydrogenase, phosphofructokinase, lactate dehydrogenase, and pyruvate kinase. Of the six enzymes examined, only hexokinase activity was increased in CEO exposed to FSH. CEO were cultured in microdrops in the presence or absence of FSH, and aliquots from the same microdrop were assayed for glucose, lactate, and pyruvate. In response to FSH, utilization of glucose in microdrop cultures by CEO was markedly increased and was accompanied by comparable lactate production and limited pyruvate production. Cycloheximide and alpha-amanitin both blocked FSH-induced oocyte maturation, but only cycloheximide prevented the increase in hexokinase activity and glucose consumption. These data suggest that hexokinase is an important rate-limiting enzyme for glucose utilization that is under translational control and participates in the mechanisms controlling the reinitiation of meiosis. However, stimulation of glycolytic activity does not appear to be a necessary concomitant for meiotic induction.

Animals↗

PubMed1996

Cyclic AMP reversal of hypoxanthine-arrested preimplantation mouse embryos is EDTA-dependent.

Hypoxanthine can block preimplantation mouse embryo development in vitro at the 2- to 4-cell stages, and this has recently been shown to be reversed by cAMP-elevating agents. However, the extent of this hypoxanthine-induced arrest is determined by the culture conditions and strain of mouse. Whitten's and KSOM/AA are two embryo culture media that support preimplantation development to the blastocyst stage. This study was undertaken to examine the influence of several components in these media on hypoxanthine-arrested preimplantation mouse embryos and to test the hypothesis that reversal of the hypoxanthine block by cAMP-elevating agents requires cooperative interaction with the chelator, EDTA. Initial experiments demonstrated that embryo development was blocked in the presence of hypoxanthine in Whitten's medium but not in KSOM/AA; furthermore, removal of EDTA from KSOM/AA rendered this medium incapable of supporting high levels of development to blastocyst (9%), whereas high numbers of blastocysts (80%) formed in Whitten's medium, which does not contain the chelator. Consequently, Whitten's medium was used to test our hypothesis. It has previously been demonstrated that the phosphodiesterase inhibitor, IBMX, can reverse the developmental arrest imposed by hypoxanthine in EDTA-supplemented Earle's basic salt solution, but in the present study the addition of IBMX to Whitten's medium resulted in a block to development and failed to reverse the hypoxanthine arrest. These disparate effects can be explained by the presence or absence of EDTA. Supplementing Whitten's medium with EDTA reverses the IBMX effect, but not the hypoxanthine-induced block. While IBMX alone is unable to reverse the hypoxanthine block in Whitten's medium, development is greatly enhanced by the simultaneous addition of EDTA and IBMX. Similar results were obtained with the cAMP analogue, 8-AHA-cAMP. The data therefore support our hypothesis that the reversal of the hypoxanthine-induced arrest by cAMP-elevating agents is critically dependent on the presence of EDTA. We contrast this with the situation in mouse oocytes, where the hypoxanthine-induced meiotic arrest is not reversed by the addition of EDTA and/or cAMP-elevating agents.

1-Methyl-3-isobutylxanthine↗

PubMed1996

The cost of treating genital warts.

BACKGROUND: Genital warts is a common sexually transmitted disease treated by a variety of medical specialists. Standard therapies offer symptomatic relief but cannot ensure lasting remission. Using the clinical literature, claims databases, and a panel of experienced practitioners, the relative efficacy, cost, and cost effectiveness of five common treatments for genital warts were assessed in this study. METHODS: We reviewed the clinical literature for the following genital wart therapies: podofilox, podophyllin, trichloroacetic acid, cryotherapy, and laser therapy, focusing on their relative efficacy. Physicians experienced in treating genital warts defined standard treatment protocols for men and women patients with moderate wart burdens. Using national claims data and protocols developed by physicians, we derived three economic models based on provider charges, third-party payments, and a resource-based relative value scale, respectively. RESULTS: The literature review demonstrated highly variable success and recurrence rates among treatment methods and failed to show that one treatment provides consistently superior efficacy. In the economic models, treating women generally proved more costly than treating men per episode of care. This was due to the need for more extensive follow-up visits in the treatment of women. Total costs were highest for cryotherapy and lowest for a patient-applied therapy that reduced the need for follow-up visits. CONCLUSIONS: Clinicians should consider both clinical and cost issues when choosing the appropriate treatment for patients with genital warts.

Clinical Protocols↗