Transfection with human thioredoxin increases cell proliferation and a dominant-negative mutant thioredoxin reverses the transformed phenotype of human breast cancer cells

Thioredoxin, a redox protein with growth factor activity that modulates the activity of several proteins important for cell growth, has been reported to be overexpressed in a number of human primary cancers. In the present study, the effects of stably transfecting mouse NIH 3T3 cells and MCF-7 human breast cancer cells with cDNA for wild-type human thioredoxin or a redox-inactive mutant thioredoxin, Cys32-->Ser32/Cys35-->Ser35 (C32S/C35S), on cell proliferation and transformed phenotype have been investigated. NIH 3T3 cells transfected with thioredoxin achieved increased saturation densities compared with vector alone-transfected cells, but were not transformed as assessed by tumor formation in immunodeficient mice. Thioredoxin-transfected MCF-7 cells showed unaltered monolayer growth on plastic surfaces compared with vector alone-transfected cells, but exhibited severalfold increased colony formation in soft agarose. Stable transfection of NIH 3T3 and MCF-7 cells with C32S/C35S resulted in inhibition of monolayer growth on plastic surfaces, and up to 73% inhibition of colony formation by MCF-7 cells in soft agarose. When inoculated into immunodeficient mice, thioredoxin-transfected MCF-7 cells formed tumors, although with a 38-57% growth rate compared with vector alone-transfected cells, whereas tumor formation by C32S/C35S-transfected MCF-7 cells was almost completely inhibited. The results of the study suggest that thioredoxin plays an important role in the growth and transformed phenotype of some human cancers. The inhibition of tumor cell growth by the dominant-negative redox-inactive mutant thioredoxin suggests that thioredoxin could be a novel target for the development of drugs to treat human cancer.

The deep branch of the ulnar nerve in Guyon's canal: branching and innervation of the hypothenar muscles

Thirty-seven embalmed, unpaired cadaver hands were dissected to delineate and classify the innervation of the hypothenar musculature. The deep branch of the ulnar nerve passed between the abductor digiti minimi and flexor digiti minimi and then pierced the opponens in all specimens. All branching occurred on the ulnar aspect of the deep branch of the ulnar nerve. A classification based on proximity of the different branches is prepared. Five different patterns have been noted.

The influence of target perturbation on manual aiming asymmetries in right-handers

Ten right-handed subjects performed 100 target-aiming movements with each hand. These movements were directed toward a small target on the midline. On 60% of the trials, the target remained stationary. On other randomly placed trials, the target "jumped" to a location 3 cm to the right (20%) or left (20%) of its original position when the cursor had travelled 6.5 cm. Although no hand differences were evident in the control condition, the right hand acquired the new target location more quickly than the left hand when the target was perturbed in either direction. Kinematic data revealed that this advantage was not due to initiating an adjustment to the initial movement more rapidly, but rather less time decelerating the corrective movement. Movement adjustments on perturbed trials were implemented more rapidly in left space than right space independent of the hand doing the aiming. These asymmetries may reflect the differential role of the two cerebral hemispheres in the control of goal-directed movements.

Dietary fatty acid modulates actions of nucleotides on humoral immune responses

Polynucleotides enhance T cell-dependent antibody production in culture. Impaired antibody production in mice fed a nucleotide-free diet can be easily restored by in vivo supplementation of both a mononucleotide-nucleoside mixture (OG-VI) and polynucleotides. Polynucleotides appear to act partly by modulating antigen presentation processes mediated by cell surface molecules. We examined whether dietary fatty acid manipulation alters nucleotides' actions on humoral immunity. Antibody production was studied in C57B1/6 mice fed I) a nucleotide-free diet high in saturated fatty acid (SFA diet), 2) a nucleotide-free diet high in polyunsaturated fatty acid (PUFA diet), and 3) a regular nucleotide-free diet (control). In vivo and in vitro T cell-dependent antibody production decreased in all groups, but mice fed the SFA diet produced more antibody in vivo than did mice in the other diet groups. Spleen cells from mice fed the SFA diet also produced more interferon-alpha when stimulated with mitogens than did those from mice fed the control diet. In contrast, polynucleotides enhanced in vitro antibody production much less efficiently in mice fed the SFA diet than in the other mice and in vivo supplementation of OG-VI was also less effective in restoring impaired antibody production in these mice. A diet with a high content of SFA may alter nucleotides' action on humoral immune responses, in addition to its direct effects on immune functions.

Phase Transitions and Critical Fluctuations in Rhythmic Coordination of Ipsilateral Hand and Foot

Four subjects performed rhythmic movements of the ankle and the wrist in time with an auditory metronome, in two modes of coordination, antiphase and in-phase. The forearm was placed in either a prone or a supine position. When movements were prepared in the antiphase mode, spontaneous transitions to the in-phase mode, or to phase wandering were observed as metronome frequency was increased. When prepared in the in-phase mode, transitions between in-phase modes or to phase wandering were occasionally observed. Predicted signature features of nonequilbrium phase transitions were noted, including loss of stability and critical fluctuations. The stability of the movement patterns was determined by spatial (dependent upon the direction of movement) rather than anatomical (dependent on the coupling of specific muscle groups) constraints. The position of the forearm had no consistent bearing upon the variability of the phase relations between the limbs, the frequency of phase transitions, or the time of onset of transitions. These results are discussed with reference to the coordination dynamics (e.g., multistability, loss of stability) of multijoint movements.

The preparation of aiming movements

Three experiments are reported in which subjects made rapid aiming movements to visual targets with their left and right hands. In Experiments 1 and 3, a precue protocol was employed. In the "simple" reaction time condition, subjects were precued with complete information concerning the target position. In the four-choice condition, subjects were precued with partial information, indicating a subset of four possible target positions. In the eight-choice condition, advance information regarding the target position was entirely ambiguous. Results indicated that when subjects were provided with unspecific advance information concerning the position of the target, and thus were unable to partially prepare movements prior to the imperative stimulus, a left hand advantage for speed of initiation was obtained. When complete advance information was available, reaction times for the left and right hands were equivalent. The left hand advantage in choice conditions was eliminated when the accuracy of response execution was emphasized and subjects were afforded the opportunity for "on-line" preparation (Experiment 3). These data are discussed in relation to the role of the right hemisphere in the preparation of movement.

Over-expression of DT-diaphorase in transfected NIH 3T3 cells does not lead to increased anticancer quinone drug sensitivity: a questionable role for the enzyme as a target for bioreductively activated anticancer drugs

Murine NIH 3T3 cells were stably transfected with human NQO1 (DT-diaphorase) cDNA and clonal cell lines with up to 15-fold elevated DT-diaphorase activity were obtained. These cell lines showed no significant increase in cell growth inhibition by the quinone anticancer drugs mitomycin C, diaziquone and menadione, when compared to vector alone transfected control cells. There was a small increase in sensitivity to doxorubicin. The relative increase in DT-diaphorase activity in the transfected cells compared to the control cell lines is similar to the increase of DT-diaphorase activity found in some human tumors compared to their paired normal tissue. The results of this study, and other evidence, suggests that DT-diaphorase may not, as suggested by others, be a clinically useful target for the bioreductive activation of anticancer drugs.

Asymmetries in Coupling Dynamics of Perception and Action

The influence of information-based dynamics on coordination dynamics of rhythmic movement was examined with special reference to the expression of asymmetries. In Experiment 1, right-handed subjects performed unimanual, rhythmical movements in coordination with either a discrete or continuous visual display. The right hand-visual display system defined a more stable perception-action collective than the left, particularly when continuous visual information was available. In Experiment 2, the same subjects performed rhythmic bimanual movements in coordination with a continuous visual display. The action collective was inherently more stable than the perception-action collective, although similar patterns were observed at both levels. Importantly, the dynamics of the perception-action collective impinged upon the dynamics of the action collective in terms of stability. Asymmetries remained evident between limbs in the bimanual preparations, with the left hand exhibiting greater limit-cycle variability and also a tendency to more often effect transitions at the action couple. Features of dynamical models that capture characteristics of manual asymmetries are discussed.

Childhood lead poisoning in Massachusetts communities: its association with sociodemographic and housing characteristics

OBJECTIVES

The purpose of the study was to examine the relationship between communities' sociodemographic and housing characteristics and incidence of lead poisoning.

METHODS

This was a population-based correlational study of 238,275 Massachusetts children from birth through 4 years of age who were screened for lead poisoning in 1991-1992. A logistic regression model was developed with the community as the unit of analysis, the case identification rate for lead poisoning (newly identified children with venous blood lead > or = 25 micrograms/dL per 1000 children) as the dependent variable, and US census variables as independent variables.

RESULTS

A significant independent relationship with the community case identification rate of lead poisoning was found for seven variables: median per capita income, percentage of housing built before 1950, percentage of the population who were Black, percentage of children screened, and a "poverty index." Rates of iron deficiency and percentage of Hispanics were not associated with the case identification rate of lead poisoning.

CONCLUSIONS

Massachusetts communities' incidence of lead poisoning is correlated with sociodemographic and housing characteristics. In states similar to Massachusetts and without screening data, this model may help target screening programs.

Systemic toxicology and laser safety of laser targeted angiography with heat sensitive liposomes

Angiography is currently limited by its lack of local and tissue specificity. The dye rapidly fills both the retinal and choroidal vessels and leaks out of the vessels thus hampering visualization of small vascular beds such as occult choroidal neovascularization. We have developed a method of laser targeted delivery based on encapsulating the dye in heat sensitive liposomes, administering the liposomes intravenously and causing them to release their content by noninvasively warming the target tissue with a laser pulse delivered through the pupil. The local release yields a bright fluorescent bolus which selectively highlights retinal or choroidal vessels. A preliminary investigation of the potential side effects of the method is presented. In rats the systemic toxicity of carboxyfluorescein-entrapped liposomes was compared with that of the free dye. No significant difference was found between the two. Non-human primates exposed to repeated laser targeted angiography were monitored over time and no significant side effects were observed. The safety of the laser exposures was assessed by conventional fluorescein angiography and histopathology. Choroidal laser targeted angiography was achieved without damage. Retinal laser targeted angiography was accompanied by mild and local damage in an area remote from the fovea. The study indicates that laser targeted choroidal angiography can be performed safely and holds promise for diseases such as age related macular degeneration with occult choroidal neovascularization. Further improvements are needed to ensure that no side effects accompany retinal laser targeted angiography.

An Elliptical Crystal Spectrometer Suitable for EXAFS Studies of Laser Compressed Materials and for High Resolution X-Ray Spectroscopy

Using an x-ray spectrometer with an elliptically curved crystal it is possible to study absorption spectra from a target placed at one focus of the ellipse using a backlighting source placed at the other focus. This principle has been used to develop a spectrometer for EXAFS studies of laser compressed materials. The backlighting source is placed at one focus of the ellipse and the laser compressed EXAFS sample at the other. Using this technique a small area of the EXAFS target can be probed, thereby minimizing any spatial variations in the compressed plasma due to nonuniformities in the laser beams. Also, the dispersive nature of the crystal ensures that it acts as a bandpass filter, so that the EXAFS sample is not probed by other x-ray wavelengths which may cause unwanted heating. Another advantage is that compressed and uncompressed EXAFS spectra can be compared on a single shot. The optical properties of the spectrometer are discussed analytically and using a computer ray-tracing program. The development and alignment of the elliptical spectrometer are discussed, and its performance using both x-ray film and a CCD detector is evaluated. The use of the elliptical spectrometer as a high-resolution x-ray instrument is presented.

Identification and mapping of Mendelian subtypes of disease

We took as our working hypothesis the premise that there could be a single locus of major effect underlying a subset of cases in the simulated Problem 2 data set, and took as our primary goal the task of mapping that locus. Treating the disease as dichotomous and using discriminant function analysis, we were able to separate affected individuals into two disease categories: Disease Type I (DT-I) cases, whose disease was by hypothesis caused by the major locus; and Disease Type II (DT-II) cases, whose disease was by hypothesis produced by other causes. Segregation analysis showed evidence of simple recessive inheritance among the DT-I individuals. Linkage analysis under the best-fitting recessive model gave clear evidence of linkage to D1G2. In the generating model, this marker is linked to a major gene for disease with recombination fraction theta = 0, and the mode of inheritance at that locus is recessive (when the trait is considered as a dichotomy). We conclude that when the true model is complex, focussing on subtypes of disease that show evidence of simple Mendelian inheritance may be a useful first step in determining the underlying model and mapping major genes.

Prompt diagnosis of ectopic pregnancy in an emergency department setting

OBJECTIVE

To evaluate quantitative hCG measurements and transvaginal ultrasound in the diagnosis of ectopic pregnancy in patients presenting to the emergency department.

METHODS

A discriminatory zone for detecting the presence or absence of an intrauterine pregnancy by transvaginal ultrasound was established prospectively. Women presenting to the emergency department were evaluated prospectively using a diagnostic algorithm consisting of clinical examination, quantitative serum hCG, and transvaginal ultrasound. Finally, ectopic pregnancies diagnosed over a 22-month period were evaluated prospectively.

RESULTS

All viable intrauterine pregnancies were identified in those subjects with hCG levels of 1500 mIU/mL (First International Reference) or greater. One thousand two hundred sixty-three subjects were evaluated prospectively; 59.8% were diagnosed with intrauterine pregnancy, 26.8% with spontaneous abortion, and 7.8% with ectopic pregnancy. At presentation, 13.2% of intrauterine pregnancies were diagnosed by clinical examination, whereas 82.9% were diagnosed by transvaginal ultrasound. Only 4% of normal intrauterine pregnancies were not confirmed on initial visit. Of 205 ectopic pregnancies diagnosed, 81.5% were hemodynamically stable; of these, 49.1% were diagnosed on initial presentation. Of all ectopics, 59% never reached an hCG level of 1500 mIU/mL and 35.8% had an hCG lower than the level at presentation. This protocol diagnosed ectopic pregnancies with a sensitivity of 100% and a specificity of 99.9%.

CONCLUSION

A protocol of quantitative hCG levels (available within hours of presentation to an emergency department) combined with transvaginal ultrasound is effective in diagnosing ectopic pregnancy.

The interaction of fentanyl on the Cp50 of propofol for loss of consciousness and skin incision

BACKGROUND

We have previously demonstrated that the minimum alveolar concentration of isoflurane at 1 atm that is required to prevent movement in 50% of patients or animals exposed to a maximal noxious stimulus is markedly reduced by increasing fentanyl concentrations. Total intravenous anesthesia with propofol is increasing in popularity, yet the propofol concentrations required for total intravenous anesthesia or the interaction between propofol and fentanyl have not yet been defined.

METHODS

Propofol and fentanyl were administered via computer-assisted continuous infusion to provide pseudo-steady-state concentrations and allow equilibration between plasma-blood concentration and their biophase concentration. For the induction of anesthesia patients were randomly allocated to receive propofol only or propofol plus fentanyl 0.2, 0.8, 1.5, 3.0, and 4.5 ng/ml. In each group patients were randomized to target propofol concentrations of 1.5-10 micrograms/ml. At 7 and 10 min arterial blood samples were taken for subsequent measurement of propofol and fentanyl concentrations. At 10 min loss of consciousness was assessed by the patients' ability to respond to a simple verbal command. Thereafter a new target concentration of propofol was entered to ensure loss of consciousness, and succinylcholine was administered to facilitate tracheal intubation. Patients were rerandomized to a new target concentration of propofol (1-19 micrograms/ml) until skin incision. Before skin incision and 1 min after skin incision, arterial blood samples were again obtained for subsequent measurement of fentanyl and propofol concentrations. At skin incision and for 1 min the patient was observed for purposeful movement. Only samples in which the pre- and poststimulus drug concentrations were within 35% of each other were included. The propofol blood concentration at which 50% or 95% of patients did not respond to verbal command (Cp50s and Cp95s, respectively) and to skin incision (Cp50i and Cp95i, respectively), were calculated by logistic regression.

RESULTS

There were 56 evaluable patients for calculating the propofol Cp50s and 53 patients for calculating the propofol Cp50i. For propofol alone the Cp50s was 3.3 micrograms/ml and the Cp95s 5.4 microgram/ml. Increasing fentanyl concentrations reduced the Cp50s (P = 0.03), and increasing age decreased the Cp50s (P = 0.04). For propofol alone the Cp50i was 15.2 (95% confidence interval 7.6-22.8) micrograms/ml and the Cp95i 27.4 micrograms/ml. Increasing fentanyl concentrations markedly reduced the Cp50i (P < 0.01), with a 50% reduction in Cp50i produced by 0.63 ng/ml fentanyl. The propofol Cp50i was decreased by 63% with 1 ng/ml fentanyl and 89% by 3 ng/ml fentanyl. At higher fentanyl concentrations the decrease in Cp50i was proportionally less, demonstrating a ceiling effect.

CONCLUSIONS

We defined the propofol concentration required for loss of consciousness and showed that it is reduced by increasing fentanyl concentration and by increasing age. The propofol concentration (alone) adequate for skin incision is high but is markedly reduced by fentanyl. A ceiling effect in the Cp50i for propofol is seen with fentanyl concentrations greater than 3 ng/ml.

Delay in the diagnosis and prognosis of carcinoma of the right colon

Of 152 consecutive patients with carcinoma of the right colon, 61 (40 per cent) suffered delays in treatment of more than 12 weeks from the onset of symptoms, with a mean delay of 48 weeks. The most common error was failure to initiate or complete the investigation of iron-deficiency anaemia (33 patients). False-negative barium enema investigations occurred in 16 cases. Patients with delays in diagnosis had survival rates not significantly different from those who presented early. Thirty-one patients with anaemia and no abdominal symptoms had a significantly higher survival rate than 30 presenting with abdominal symptoms, despite delays in treatment (P < 0.02). Greater vigilance is required in the investigation of patients presenting with iron-deficiency anaemia.

Plasma concentration of fentanyl, with 70% nitrous oxide, to prevent movement at skin incision

BACKGROUND

The Cp50 (minimal steady state plasma concentration of an intravenous analgesic/anesthetic required to prevent a somatic response in 50% of patients following skin incision) and the Cp50-BAR (minimal plasma concentration of an analgesic/anesthetic required to prevent either a somatic, hemodynamic, or autonomic response in 50% of patients following skin incision) have been recently proposed as a measure, like minimum alveolar concentration (MAC; and MAC-BAR), to establish the relative potency of intravenous analgesics. This study was conducted to establish the Cp50 for fentanyl.

METHODS

Unpremedicated patients were administered fentanyl (in the presence of 70% N2O) via computer-assisted continuous infusion, a pharmacokinetic model-driven infusion device. After induction of anesthesia with fentanyl, the randomized target fentanyl concentration was entered into computer-assisted continuous infusion. This target fentanyl concentration was maintained until skin incision. Before induction, prior to skin incision, and immediately after skin incision, arterial blood samples were obtained for measurement of fentanyl and norepinephrine concentrations. At skin incision, patients were observed for a somatic, hemodynamic, or autonomic response. Only patients in whom the pre- and postincision fentanyl concentrations were within +/- 30% were included in the calculation of the Cp50. The Cp50 was calculated using logistic regression.

RESULTS

The Cp50 for fentanyl was 3.26 ng/ml, and the Cp50-BAR was 4.17 ng/ml.

CONCLUSIONS

Comparing these results with the previously published Cp50 of alfentanil, the potency of fentanyl relative to alfentanil is 1:58. Establishing the Cp50, once effect site equilibration has occurred, will allow pharmacodynamic comparisons between the opioids at equipotent concentrations.

Isoflurane minimum alveolar concentration reduction by fentanyl

BACKGROUND

Isoflurane is commonly combined with fentanyl during anesthesia. Because of hysteresis between plasma and effect site, bolus administration of fentanyl does not accurately describe the interaction between these drugs. The purpose of this study was to determine the MAC reduction of isoflurane by fentanyl when both drugs had reached steady biophase concentrations.

METHODS

Seventy-seven patients were randomly allocated to receive either no fentanyl or fentanyl at several predetermined plasma concentrations. Fentanyl was administered using a computer-assisted continuous infusion device. Patients were also randomly allocated to receive a predetermined steady state end-tidal concentration of isoflurane. Blood samples for fentanyl concentration were taken at 10 min after initiation of the infusion and before and immediately after skin incision. A minimum of 20 min was allowed between the start of the fentanyl infusion and skin incision. The reduction in the MAC of isoflurane by the measured fentanyl concentration was calculated using a maximum likelihood solution to a logistic regression model.

RESULTS

There was an initial steep reduction in the MAC of isoflurane by fentanyl, with 3 ng/ml resulting in a 63% MAC reduction. A ceiling effect was observed with 10 ng/ml providing only a further 19% reduction in MAC. A 50% decrease in MAC was produced by a fentanyl concentration of 1.67 ng/ml.

CONCLUSIONS

Defining the MAC reduction of isoflurane by all the opioids allows their more rational administration with inhalational anesthetics and provides a comparison of their relative anesthetic potencies.

Asymmetries in the regulation of visually guided aiming

An experiment was conducted to examine the contribution of sensory information to asymmetries in manual aiming. Movements were performed in four vision conditions. In the full-vision condition (FV), subjects were afforded vision of both the hand and the target throughout the course of the movement. In the ambient-illumination-off condition (AO), the room lights were extinguished at movement initiation, preventing vision of the moving limb. In the target-off (TO) condition, the target was extinguished upon initiation of the movement. In a no-vision (NV) condition, ambient illumination was removed and the target was extinguished upon initiation of the response movement. Results indicated that accuracy was superior in the full-vision and target-off conditions and when movements were made by the right hand. Movements made by the right hand were also of shorter mean duration. The magnitudes of performance asymmetries were uninfluenced by vision condition. Analyses of movement kinematics revealed that movements made in conditions in which there was vision of the limb exhibited a greater number of discrete modifications of the movement trajectory. On an individual-trial basis, no relationship existed between accuracy and the occurrence of discrete modifications. These data suggest that although vision greatly enhances accuracy, discrete modifications subserved by vision reflect the imposition of nonfunctional zero-order control processes upon continuous higher-order control regimes.

Treatment of antineutrophil cytoplasmic autoantibody-positive systemic vasculitis and glomerulonephritis with pooled intravenous gammaglobulin

Antineutrophil cytoplasmic autoantibody (ANCA) is considered a serological marker for disease activity in patients with ANCA(+) systemic vasculitis. Recently, ANCA has been implicated as a pathogenic antibody that may be associated with neutrophil degranulation and release of lytic enzymes. Since intravenous gammaglobulin (IVIG) is known to contain antiidiotypic antibodies to ANCA, which could decrease the activity of the later, we chose to treat two patients with symptomatic ANCA(+) systemic vasculitis and glomerulonephritis with high-dose IVIG. The first patient, a 66-year-old man, developed rapidly progressive renal failure despite treatment with intravenous (IV) cyclophosphamide. The second patient, a 14-year-old boy, had relapsed 3 months after cessation of treatment with prednisone and cyclophosphamide. Both patients improved dramatically after treatment with IVIG, with the former recovering renal function within 11 days of therapy. In both patients, a concomitant reduction in serum ANCA titers was also observed. The second patient is currently in a sustained remission 14 months after his last IVIG dose on no other medication. These cases provide clinical evidence that IVIG has therapeutic benefit in modifying the immune-mediated injury associated with ANCA(+) systemic vasculitis and glomerulonephritis. In addition, IVIG may provide an additional safe therapeutic option to clinicians treating patient's with ANCA(+) vasculitis and glomerulonephritis who are not responsive to or are experiencing toxicity from conventional therapy.

Asymmetries in the spatial localization of transformed targets

This study was designed to examine the contribution of the right cerebral hemisphere in the spatial localization of visual targets for manual aiming. Visual targets were briefly presented to the right and left fields and subjects were required to point either to the target location, or a "mirror" image of the target location with their right or left index finger. Whereas reaction times were faster for left-hand pointing than for right-hand pointing, there was no differential effect of the mirror image transformation. This suggests that left-hand reaction time advantages are more related to right hemisphere involvement in the spatial parameterization of the movement than spatial localization of the target.

Fentanyl does not alter the "sleep" plasma concentration of thiopental

Thiopental and fentanyl are commonly combined for induction of anesthesia. The effect of an analgesic concentration of fentanyl on the plasma concentration of thiopental to induce sleep was studied in 46 unpremedicated patients. As a measure of drug effect, sleep (the lack of response to open eyes to a verbal command) was used. Forty-six patients were randomized to receive thiopental infused to one of several predetermined plasma concentrations. Twenty-two of these patients also received a fentanyl infusion to a desired analgesic concentration of 1 ng/mL. Thiopental and fentanyl were infused by means of a pharmacokinetic model-driven infusion device (computer-assisted continuous infusion, CACI). Venous blood samples were taken from the contralateral antecubital fossa at 5 and 10 min after the start of the infusion. At 10 min, the patients' names were firmly spoken, and they were instructed to open their eyes. If they did not respond to this command, they were considered to be asleep. Only patients in whom the 5- and 10-min measured plasma concentrations of thiopental and fentanyl, respectively, were within +/- 30% of each other were used for the determination of the Cp50(asleep), the plasma concentration at which 50% of the patients were asleep. The Cp50(asleep) with and without fentanyl was calculated by logistic regression. The Cp50(asleep) for patients in whom concentrations were maintained within +/- 30% for thiopental alone (n = 17) was 7.32 micrograms/mL (95% confidence interval, 5.53-10.95); for thiopental in the presence of fentanyl (n = 18 with a measured fentanyl concentration of 1.27 +/- 0.5 ng/mL), this was 7.22 micrograms/mL (95% confidence interval, 4.83-10.15).(ABSTRACT TRUNCATED AT 250 WORDS)