Cocaine: mechanism of inhibition of a muscle acetylcholine receptor studied by a laser-pulse photolysis technique

Effects of cocaine on the muscle nicotinic acetylcholine receptor were investigated by using a chemical kinetic technique with a microsecond time resolution. This membrane-bound receptor regulates signal transmission between nerve and muscle cells, initiates muscle contraction, and is inhibited by cocaine, an abused drug. The inhibition mechanism is not well understood because of the lack of chemical kinetic techniques with the appropriate (microsecond) time resolution. Such a technique, utilizing laser-pulse photolysis, was recently developed; by using it the following results were obtained. (i) The apparent cocaine dissociation constant of the closed-channel receptor form is approximately 50 microM. High carbamoylcholine concentration and, therefore, increased concentrations of the open-channel receptor form, decrease receptor affinity for cocaine approximately 6-fold. (ii) The rate of the receptor reaction with cocaine is at least approximately 30-fold slower than the channel-opening rate, resulting in a cocaine-induced decrease in the concentration of open receptor channels without a concomitant decrease in the channel-opening or -closing rates. (iii) The channel-closing rate increases approximately 1.5-fold as the cocaine concentration is increased from 20 to 60 microM but then remains constant as the concentration is increased further. The results are consistent with a mechanism in which cocaine first binds rapidly to a regulatory site of the receptor, which can still form transmembrane channels. Subsequently, a slow step (t1/2 approximately 70 ms) leads to a receptor form that cannot form transmembrane channels, and acetylcholine receptor-mediated signal transmission is, therefore, blocked. Implications for the search for therapeutic agents that alleviate cocaine poisoning are mentioned.     

Comparison of extraction methods and detection systems in the gas chromatographic analysis of volatile carbonyl compounds

High-resolution gas chromatography (HRGC) with electron-capture detection (ECD), nitrogen-phosphorus detection (NPD), flame ionization detection (FID) or with mass spectrometry-selected ion monitoring (MS-SIM) was used in the analysis of volatile carbonyl compounds. Eighteen carbonyl compounds that are typically produced during lipid peroxidation were derivatized quantitatively with pentafluorophenylhydrazine (PFPH) at room temperature, to afford their corresponding water-insoluble hydrazones. These derivatives were extracted into non-polar phases by means of either liquid-liquid extraction (LLE) (hexane) or solid-phase extraction (SPE) on 3 ml C18 octadecyl-bonded phase cartridges. Detection limits of 10(-14) and 10(-12) mol/ml per aldehyde were achieved with the ECD and MS-SIM systems, respectively. The effects of extraction conditions on sensitivity and recovery were determined by performing parallel HRGC-ECD and HRGC-MS-SIM analyses of pentafluorophenylhydrazones of the eighteen compounds under study. Recoveries of 51.4-78.9 +/- 1.2-4.5 and 80.9-98.3 +/- 1.0-3.5% were obtained with LLE and SPE, respectively. The method was applied to the analysis of the volatile carbonyl compounds in various heated vegetable oils (corn, palm or sunflower) and to the analysis of volatile aldehydes in human urine.     

Mutations in purine nucleoside phosphorylase deficiency

PURPOSE: The aim of this study was to investigate the incidence of unexpected malignant uveal melanoma in the age of ultrasound diagnostics and to highlight the reasons for misdiagnosis. PATIENTS AND METHODS: All eyes were surgically removed and histologic examination was performed between 1981 and 1995. The eyes were investigated for the incidence of uveal melanoma, and the history of the unexpected malignant melanoma of the uvea or ciliary body highlighted. RESULTS: 225 (18.7%) eyes with malignant melanoma out of 2583 enucleated eyes were found. Eight (3.6%) of 225 were clinically unexpected. The clinical misdiagnoses were secondary angle closure or open angle glaucoma (6), retinal detachment (5), iritis (1), scleritis (1), cataract (4) and an intraocular mass that was believed to be a metastasis of a colon carcinoma. Seven of eight eyes were blind, and one eye had light perception only. The longest follow up before enucleation was 13 years. On three eyes diagnostic ultrasound was reportedly performed without specific diagnosis of uveal melanoma. Surgery was performed on four eyes for reasons of uncontrollable intraocular pressure or retinal detachment up to five years before enucleation. Histologic diagnoses were 3 epitheloid-type, 2 spindel-type and 3 necrotic melanoma of the uvea. Four eyes showed scleral invasion by tumor cells and one eye an invasion into the episcleral space. CONCLUSIONS: Even today the rate of unexpected uveal melanoma, according to our study is 3.6%. Therefore, all blind eyes without visualisation of the posterior pole should be examined with ultrasound in order to diagnose an uveal melanoma prior to enucleation.     

The nervous system function of patients with periodontitis

Analysis of the function of the nervous system, based on clinical, neurological, and psychological studies in 78 patients with generalized periodontitis, revealed central regulation disorders without signs of organic lesions of the brain in 76% patients. The authors claim that stress and a high level of personal anxiety may be responsible for the development of these disorders, which was confirmed by the results of psychological testing.     

Arterial oxygen saturation in Tibetan and Han infants born in Lhasa, Tibet

BACKGROUND: Reduced oxygen availability at high altitude is associated with increased neonatal and infant mortality. We hypothesized that native Tibetan infants, whose ancestors have inhabited the Himalayan Plateau for approximately 25,000 years, are better able to maintain adequate oxygenation at high altitude than Han infants, whose ancestors moved to Tibet from lowland areas of China after the Chinese military entered Tibet in 1951. METHODS: We compared arterial oxygen saturation, signs of hypoxemia, and other indexes of neonatal wellbeing at birth and during the first four months of life in 15 Tibetan infants and 15 Han infants at 3658 m above sea level in Lhasa, Tibet. The Han mothers had migrated from lowland China about two years previously. A pulse oximeter was placed on each infant's foot to provide measurements of arterial oxygen saturation distal to the ductus arteriosus. RESULTS: The two groups had similar gestational ages (about 38.9 weeks) and Apgar scores. The Han infants had lower birth weights (2773 +/- 92 g) than the Tibetan infants (3067 +/- 107 g), higher concentrations of cord-blood hemoglobin (18.6 +/- 0.8 g per deciliter, vs. 16.7 +/- 0.4 in the Tibetans), and higher hematocrit values (58.5 +/- 2.4 percent, vs. 51.4 +/- 1.2 percent in the Tibetans). In both groups, arterial oxygen saturation was highest in the first two days after birth and was lower when the infants were asleep than when they were awake. Oxygen saturation values were lower in the Han than in the Tibetan infants at all times and under all conditions during all activities. The values declined in the Han infants from 92 +/- 3 percent while they were awake and 90 +/- 5 percent during quiet sleep at birth to 85 +/- 4 percent while awake and 76 +/- 5 percent during quiet sleep at four months of age. In the Tibetan infants, oxygen saturation values averaged 94 +/- 2 percent while they were awake and 94 +/- 3 percent during quiet sleep at birth and 88 +/- 2 percent while awake and 86 +/- 5 percent during quiet sleep at four months. Han infants had clinical signs of hypoxemia--such as cyanosis during sleep and while feeding--more frequently than Tibetans. CONCLUSIONS: In Lhasa, Tibet, we found that Tibetan newborns had higher arterial oxygen saturation at birth and during the first four months of life than Han newborns. Genetic adaptations may permit adequate oxygenation and confer resistance to the syndrome of pulmonary hypertension and right-heart failure (subacute infantile mountain sickness).     

Intensive care unit prognostic scoring systems to predict death: a cost-effectiveness analysis

OBJECTIVE: To evaluate the cost-effectiveness, using the technique of decision analysis, of withdrawing care from patients in the intensive care unit (ICU) who are predicted to have a high probability of death (>90%) after 48 hrs using a mortality risk estimate based on daily Acute Physiology and Chronic Health Evaluation (APACHE) III scores. MATERIALS AND METHODS: A decision tree model was constructed to compare the cost-effectiveness of two clinical strategies. In the first strategy, patients receive ICU care until they were discharged, died, or had care withdrawn based on subjective clinical criteria. In the second strategy, patients remained in the ICU until they were either discharged, died, or had life-sustaining care withdrawn based on subjective criteria or if they were predicted to have a >90% risk of mortality after 48 hrs by a prognostic scoring system. Transition probabilities were based on a retrospective data analysis of 4,106 noncardiac ICU patients admitted to a tertiary surgical ICU over a 9-yr period. Cost estimates were based on daily Therapeutic Intervention Scoring System (TISS) scores from our database and using published data on the estimated production cost for a TISS point. The sensitivity (16.6%) and specificity (99.6%) of the mortality risk estimate at 48 hrs (using the >90% decision point) based on daily APACHE III scores were derived from published data. RESULTS: In the base case analysis, we assumed that the sensitivity and specificity of the prognostic risk estimate are unchanged when exported to a new environment. Not using a prognostic scoring system as the basis for withdrawing care resulted in a slightly higher survival rate (87.2% vs. 86.85%) at a cost-per-death prevented (CPDP) of $263,700. Since prognostic scoring systems have not been shown to retain the same predictive power when exported to new databases, we chose to explore the effect of varying the specificity of the scoring system on CPDP. Decreasing the specificity from .996 (baseline) to .98 causes the CPDP to drop to $53,300. Changing the specificity to .95 results in a CPDP prevented of $21,700. Using one-way sensitivity analysis, the CPDP is shown to be relatively insensitive to delaying the decision point from ICU day 3 to day 7. Sensitivity analysis also indicates that CPDP increases rapidly with hospital death rate. For a death rate of 30%, the CPDP increases to $768,600 (in the base case, the death rate is 12.8%); when the specificity is decreased to .95, the CPDP drops to $62,100. CONCLUSION: Unless daily mortality risk estimates based on APACHE III can be shown to retain the same level of predictive power in ICUs outside the development database, it is unlikely that the incremental cost-effectiveness gained by using them as the basis to withdraw care is sufficient to justify their use in this manner.     

Low density lipoprotein of synovial fluid in inflammatory joint disease is mildly oxidized

The histologic diagnosis of adult renal epithelial neoplasms with prominent eosinophilic cytoplasm (renal oncocytoma, chromophobe renal-cell carcinoma (RCC), eosinophilic variant of clear-cell RCC, eosinophilic variant of papillary RCC, and collecting duct carcinoma), could be problematic in some cases because of overlapping morphologic features. Precise diagnosis is essential, however, because it often connotes a distinct biologic behavior. Proliferative activity has not been specifically investigated in this spectrum of renal tumors, so we studied the MIB-1 proliferation index in 20 renal oncocytomas, 12 chromophobe RCCs, 9 eosinophilic variants of papillary RCCs, and 13 eosinophilic variants of clear-cell RCCs. Our purpose was to identify the biologic potential of these renal tumors on the basis of MIB-1 tumor proliferation index and to ascertain whether that index had diagnostic value. Overall, nuclear grade correlated with MIB-1 tumor proliferation index (P=.03). The mean proliferation index progressively increased from renal oncocytomas (0.3) to chromophobe RCCs (0.8) to eosinophilic variants of papillary RCCs (2.2) to eosinophilic variants of clear-cell RCCs (4.1) (P=.002). None of the renal oncocytomas or chromophobe RCCs had an index greater than 2, whereas 8 of 13 eosinophilic variants of clear-cell RCCs had an index greater than 2; in 5 of these, it was more than 3. Thus, in the differential diagnosis between renal oncocytoma/chromophobe RCC and eosinophilic variant of RCC, an MIB-1 index of greater than 3 with appropriate morphologic correlation would strongly support the diagnosis of the latter. We also concluded that the progressive increase in MIB-1 tumor proliferation index across the spectrum of granular renal-cell neoplasms parallels the emerging data in the current literature concerning the biologic potential of adult renal epithelial tumors and justifies histologic categorization of adult renal epithelial neoplasms.