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Biomedical subjects

J W Lewis

Publications and source records attributed to J W Lewis.

At least 19 recordsLinked to original sources
PubMed1992

Photointermediates of visual pigments.

Much progress has been made in recent years toward understanding the interactions between various proteins responsible for visual transduction which are initiated by an activated state of visual pigments. However, the changes which take place in the visual pigments themselves to convert them to the activated state are more poorly understood. Many spectroscopic techniques have been applied to this problem in recent years and considerable progress has been made. A major goal of these efforts is to understand at which stages protein change occurs and to characterize its structural features. In the visual system evidence is accumulating, for example, that chromophore independent protein change begins immediately prior to lumirhodopsin formation. Considerable insight has been gained recently into the early intermediates of visual transduction and the stage is set to achieve similar understanding of the later intermediates leading to rhodopsin's activated state.

Photolysis↗
PubMed1992

The utility of a double-lumen tube for one-lung ventilation in a variety of noncardiac thoracic surgical procedures.

To determine the utility of one-lung ventilation (OLV) in a variety of noncardiac thoracic surgical procedures, 200 patients were studied to document the ease of double-lumen tube (DLT) placement, associated complications, intraoperative respiratory changes, and methods for managing hypoxic events. Most tubes could be placed, repositioned when necessary, and secured within 12 minutes. By defining tube position with fiberoptic bronchoscopy, auscultatory assessment of placement was found to be incorrect in 38.0% of patients. The tip occluded the respective upper lobe orifice in 40.5% of this subgroup, the endobronchial cuff was at or above the carina in 38.7%, and in the wrong mainstem bronchus in 20.8%. During OLV, PaO2 initially fell to approximately 200 mmHg in most patients but gradually rose during the balance of the operation. Hypoxia (PaO2 less than 80 mmHg) during OLV developed in 28.5% of patients. Preoperative spirometry and arterial blood gases had no predictive value for this complication. Pulse oximetry values between 95% and 100% reliably reflected systemic arterial oxygen saturation. Hypoxia occurring during OLV was successfully reversed in 40.0% of instances by positive end-expiratory pressure (PEEP) to the ventilated lung. The addition of continuous positive airway pressure (CPAP) to the nonventilated lung reversed persistent hypoxia in virtually all cases. There was no difference in oxygenation, carbon dioxide elimination, airway pressures, or intraoperative complications noted between right and left double-lumen tubes. In conclusion, a DLT for OLV can expeditiously and safely be placed. Because auscultation for tube position is unreliable, bronchoscopic assessment of final position should be performed in every instance. Hypoxia during OLV can be detected reliably by pulse oximetry.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Sites of encystment by the metacercariae of Echinoparyphium recurvatum in Lymnaea peregra.

Experimental infection of Echinoparyphium recurvatum von Linstow (Digenea: Echinostomatidae) cercariae in the snail second intermediate host Lymnaea peregra Müller shows that metacercarial encystment takes place on the lining of the mantle cavity, pericardial cavity and kidney lumen, with the mantle cavity the most preferred site. All three sites are accessible via the body openings. The metacercariae appear to be more susceptible to encapsulation in the visceral mass than in the cavity of the mantle, pericardium and the lumen of the kidney.

Animals↗
PubMed1992

The laboratory maintenance of Sanguinicola inermis Plehn, 1905 (Digenea: Sanguinicolidae).

Methodology is described for the laboratory maintenance of the life-cycle of Sanguinicola inermis, using common carp (Cyprinus carpio) as the definitive host and Lymnaea peregra as the intermediate host. Lymnaea auricularia was also infected but is not considered to be a suitable laboratory host. Tench (Tinca tinca) were susceptible to infection at high cercarial doses but subsequent infection rates were low. Goldfish (Carassius auratus) and Lymnaea stagnalis were refractory to laboratory infection.

Animals↗
PubMed1992

Photolysis of rhodopsin results in deprotonation of its retinal Schiff's base prior to formation of metarhodopsin II.

Absorption changes following photolysis of bovine rhodopsin in mildly sonicated membrane suspensions are monitored at 25 degrees C. Difference spectra collected at 17 times between 1 microsecond and 75 ms following excitation are analyzed globally using singular value decomposition and non-linear least-squares fitting techniques. The results are not consistent with the simple scheme: Lumirhodopsin-->Metarhodopsin I<-->Metarhodopsin II, but indicate that an intermediate with a deprotonated Schiff's base is formed nearly simultaneously with metarhodopsin I upon the decay of Lumirhodopsin.

Animals↗
PubMed1992

Clocinnamox: a novel, systemically-active, irreversible opioid antagonist.

The warm water (55 degrees C) tail-withdrawal procedure was used to assess the analgesic effects of the prototypic mu opioid agonists, morphine and fentanyl, in mice. Both drugs produced full analgesic effects under these conditions, which were dose-dependently antagonized by naltrexone. The pA2 values for naltrexone with morphine and with fentanyl were not significantly different. Low doses (e.g., 0.32 mg/kg) of clocinnamox [C-CAM.14 beta-(p- chlorocinnamoylamino)-7,8-dihydro-N-cyclopropylmethylnormorphin one mesylate] produced rightward shifts in the dose-effect curves for each drug, whereas high doses (e.g., 32 mg/kg) depressed the maximal analgesic response. In addition, it was observed that higher doses of C-CAM were required to produce a shift down in the fentanyl dose-effect curve than were required to produce a shift down in the morphine dose-effect curve, which suggests that fentanyl is more efficacious than morphine. The highest dose of C-CAM (32 mg/kg) antagonized the analgesic effect of morphine for up to 8 days. In contrast, the antagonist activity of naltrexone (100 mg/kg) against morphine lasted for only 2 days. Finally, when naloxone was administered simultaneously with 32 mg/kg C-CAM 2 days before determination of the morphine dose-effect function, the antagonist effect of C-CAM was prevented in a dose-dependent manner. Taken together, these results suggest that C-CAM may be producing its antagonist action at opioid receptors through a nonequilibrium mechanism.

Analgesia↗
PubMed1992

Scanning electron microscope and histological studies of rare triradiate forms of Taenia pisiformis from dogs in Cairo.

Of 5,404 domestic dogs examined for normal and abnormal Taenia pisiformis in Cairo, Egypt, one dog contained 3 triradiate specimens while 3,569 harboured one or more normal cestodes. The study revealed a ratio of one triradiate to 5,620 normal adult worms in the parasite population and a prevalence of 0.02% for the triradiate forms. Polyradiate forms are far less common in this large survey than has been indicated in previous reports.

Animals↗
PubMed1991

Photolysis intermediates of human rhodopsin.

Photochemical studies were conducted on human rhodopsin at 20 degrees C to characterize the intermediates which precede the formation of metarhodopsin II, the trigger for the enzyme cascade mechanism of visual transduction. Human rhodopsin was prepared from eyes which had previously been used for corneal donations. Time resolved absorption spectra collected from 10(-8) to 10(-6) s after photolysis of human rhodopsin in detergent suspensions displayed biexponential decay kinetics. The apparent lifetimes obtained from the data are 65 +/- 20 and 292 +/- 25 ns, almost a factor of 2 slower than the corresponding rates in bovine rhodopsin. The spectra can be fit well using a model in which human bathorhodopsin decays toward equilibrium with a blue-shifted intermediate (BSI) which then decays to lumirhodopsin. Spectra and kinetic rate constants were determined for all these intermediates using a global analysis which showed that the spectra of the human intermediates are remarkably similar to bovine intermediates. Microscopic rate constants derived from this model are 7.4 x 10(6) s-1 for bathorhodopsin decay and 7.5 x 10(6) s-1 and 4.6 x 10(6) s-1 for the forward and reverse reactions of BSI, respectively. Decay of lumirhodopsin to later intermediates was studied from 10(-6) to 10(-1) s after photolysis of rhodopsin in human disk membrane suspensions. The human metarhodopsin I in equilibrium metarhodopsin II equilibrium appears to be more forward shifted than in comparable bovine studies.

Humans↗
PubMed1991

Comparison of isolates and species of Toxocara and Toxascaris by biosynthetic labelling of somatic and ES proteins from infective larvae.

Infective-stage larvae of three different isolates of Toxocara canis were intrinsically ([35S]methionine) labelled in culture, to determine the presence of similarities or differences in the somatic and ES antigens expressed between larvae derived from different hosts and different geographical regions. Two other closely related ascaridids, Toxascaris leonina which infects cats and dogs, and Toxocara vitulorum (Neoascaris vitulorum) which infects cattle, were also compared to T. canis larvae by this method. Overall comparisons were made by 1- and 2-dimensional electrophoresis, while immunological cross-reactivities between the different species were analysed by radio-immunoprecipitation. Our results show that extensive physicochemical characteristics are shared between T. canis isolates, both from different hosts and different geographical locations. A substantial overlap was revealed when T. canis and T. vitulorum antigens were compared, whereas Toxascaris was found to produce a distinct antigen profile: this result was independent of whether methionine- or Iodogen-labelled products were being considered. Antigen recognition by polyclonal antibodies raised to all three species and to the cat ascaridid Toxocara cati, revealed considerable cross-reactivities. The cross-reactions were especially prominent between the Toxocara species, a fact further substantiated when reactivity of T. canis ES-specific monoclonal antibodies were tested against T. leonina and T. vitulorum antigens. The ES antigens of T. leonina were not recognized by the T. canis monoclonals, whereas the majority of these antibodies precipitated antigens of T. vitulorum. One which did not react with T. vitulorum was monoclonal antibody Tcn 2, indicating its species-specific reactivity and therefore its potential for the specific diagnosis of human toxocariasis.

Animals↗
PubMed1991

Rotational diffusion effects on absorbance measurements: limitations to the magic-angle approach.

Optical absorbance changes are commonly used to characterize intermediates which appear in the bleaching sequence of rhodopsin and in the photocycle of bacteriorhodopsin. Absorbance changes can be caused by an intermediate's rotational diffusion, and when this occurs it can distort absorbance changes due to the structural evolution of intermediates. Linear polarization of an optical probe source at 54.7 degrees (the magic angle) relative to the polarization direction of a linearly polarized actinic source has often been used to eliminate signals due to rotational diffusion. We used Jones calculus to investigate the validity of the magic-angle strategy. Taylor expansion of the result in powers of the absorbances of the bleached ground state and of the intermediates leads to a relatively simple expression which can be used to determine whether rotational contributions are likely under various experimental conditions. This expression shows that in first order no dichroism-dependent term appears in the absorbance measured at magic angle. In second order, however, linear dichroism contributes to signals. For the sequence of rhodopsin intermediates: rhodopsin hv----bathorhodopsin in equilibrium BSI----lumirhodopsin, where BSI is a recently discovered blue-shifted intermediate, we determined the magnitude of the dichroism signals to be, on average, less than 2% of the true absorbance change due to the intermediates themselves (and hence undetectable). Freedom from dichroism artifacts in this case results from the fact that the transition dipoles of these intermediates are similar to that of rhodopsin. Larger and certainly detectable dichroism signals are predicted to occur, even at the magic angle, for later intermediates which have transition dipole moments which differ significantly from that of rhodopsin.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriorhodopsins↗
PubMed1991

Transthoracic and transesophageal echocardiography in the diagnosis and surgical management of right atrial myxoma.

An asymptomatic patient was discovered to have a large right atrial myxoma by transthoracic echocardiography. Preoperative considerations included the possibility of satellite lesions, left atrial origin, and a question of tricuspid valve involvement. Subsequent operative transesophageal echocardiography demonstrated single-stalk attachment in the right atrial septal wall and no satellite lesions. Doppler and color flow examination immediately following tumor removal aided in the decision not to perform tricuspid annuloplasty as there was no significant tricuspid regurgitation. The combined use of transthoracic and transesophageal echocardiography with Doppler and color flow imaging aids in the preoperative and intraoperative diagnosis and surgical management of right atrial tumors.

Echocardiography↗
PubMed1991

The epidemiology of Taenia pisiformis infections in domestic dogs in Cairo.

The epidemiology of Taenia pisiformis infections in domestic dogs in Cairo, Egypt. Over 5000 street dogs humanely killed in a culling programme organized by the Egyptian Ministry of the Interior in the winter of 1986 and the spring of 1987 have been utilized to examine the final host epidemiology of the cestode Taenia pisiformis in Cairo. In the winter months the prevalence of infection was 63.4% and the mean intensity 2.82 per dog: by the spring of 1987 these values had risen to 70.8% and 3.78 respectively. These parasite burdens probably represent the highest infection levels with T. pisiformis yet described from urban dog populations anywhere in the world. The dispersion of T. pisiformis within the street dog population was assessed and found to be significantly aggregated and well described by a negative binomial model of overdispersion (variance/mean ratio: 5.16, coefficient k = 0.795). A separate analysis was carried out of infection in each of 18 circumscribed regional areas of Cairo which revealed considerable area-to-area differences with mean intensities varying between 1.62 and 6.54 and prevalences between 43.3% and 91.2%. The size structure of the winter and spring worm samples were very similar with about 45% of worms less than 35 cm in length, about 35% between 35 and 59 cm, about 20% between 60 and 100 cm and less than 5% greater than 100 cm in length. The epidemiological factors which lead to high T. pisiformis infection levels in Cairo dogs have been considered and the consumption of discarded rabbit offal containing Cysticercus pisiformis by street dogs is regarded as a crucial mode of transmission.

Animals↗
PubMed1991

Spectrophotometric quantitation of rhodopsin in the human retina.

The rhodopsin content of the human retina was determined spectrophotometrically. Retinas were removed completely by using an in vitro technique based on a simulation of retinal detachment. This method provides a total recovery of rod outer segments which contain the rhodopsin visual pigment or its apoprotein, opsin. Using this improved dissection method followed by a crude preparation of the retina, an opsin-rhodopsin content of 6.20 +/- 0.64 nmol/retina (n = 9) was found. This is larger than values previously reported. Regeneration with a threefold excess of 11-cis-retinal improved the recovery of rhodopsin dramatically because the corneas of these human donor eyes were removed for corneal transplant surgery under relatively bright light that bleaches the retina nearly completely. The amount of rhodopsin that can be isolated will be sufficient for studies on early events in visual transduction using laser photolysis.

Adult↗
PubMed1990

Nanosecond photolysis of rhodopsin: evidence for a new, blue-shifted intermediate.

Early photolysis intermediates of native bovine rhodopsin (RHO) are investigated by nanosecond laser photolysis near physiological temperature. Absorption difference spectra are collected after excitation with 477-, 532-, and 560-nm laser pulses of various energies and with 477-nm laser excitation at 5, 12, 17, 21, and 32 degrees C. The data are analyzed by using singular-value decomposition (SVD) and a global exponential fitting routine. Two rate constants associated with distinct spectral changes are observed during the time normally associated with the decay of bathorhodopsin to lumirhodopsin. Various models consistent with this observation are considered. A sequential model in which there is a reversible step between a bathorhodopsin intermediate and a new intermediate (BSI), which is blue-shifted relative to lumirhodopsin, is shown to best fit the data. The temperature dependence of the observed and calculated rate constants leads to linear Arrhenius plots. Extrapolation of the temperature dependence suggests that BSI should not be observable after rhodopsin photolysis at temperatures below -100 degrees C. The results are discussed with regard to the artificial visual pigments cis-5,6-dihydroisorhodopsin and 13-demethylrhodopsin. It is proposed that the rate of the BATHO to BSI transition is limited by the relaxation of the strained all-trans-retinal chromophore within a tight protein environment. The transition to LUMI involves chromophore relaxation concurrent with protein relaxation. While the first process is strongly affected by changes in the chromophore, the second transition seems to be determined more by protein relaxation.

Chemical Phenomena↗