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Biomedical subjects

J Schenck

Publications and source records attributed to J Schenck.

16 recordsLinked to original sources
PubMed2000

Differential effects of protein kinase C on the levels of epithelial Na+ channel subunit proteins.

Regulation of epithelial Na(+) channel (ENaC) subunit levels by protein kinase C (PKC) was investigated in A6 cells. PKC activation altered ENaC subunit levels, differentially decreasing the levels of both beta and gamma, but not alphaENaC. Temporal regulation of beta and gammaENaC by PKC differed; gammaENaC decreased with a time constant of 3.7 +/- 1.0 h, whereas betaENaC decreased in 13.9 +/- 3. 0 h. Activation of PKC also resulted in a decrease in trans-epithelial Na(+) reabsorption for up to 48 h. PMA activation of PKC resulted in negative feedback inhibition of PKC protein levels beginning within 4 h. Both beta and gammaENaC levels, as well as transport tended toward pretreatment values after 48 h of PMA treatment. PKC inhibitors attenuated the effects of PMA on ENaC subunit levels and Na(+) transport. These results directly show for the first time that PKC differentially regulates ENaC subunit levels by decreasing the levels of beta and gamma but not alphaENaC protein. These results imply a PKC-dependent, long term decrease in Na(+) reabsorption.

Aldosterone↗
PubMed2000

Does gastroscopy induce myocardial ischemia in patients with coronary heart disease?

BACKGROUND AND STUDY AIMS: Gastroscopy has been reported to be dangerous for unstable patients with coronary heart disease (CHD). The aims of this study were to find out whether endoscopy is equally liable to cause myocardial ischemia in stable CHD patients, and whether this can be predicted prior to endoscopy, and to find out the frequency of abnormal findings in patients for whom a secondary prophylaxis with acetylsalicylic acid (ASA) is indicated. PATIENTS AND METHODS: Electrocardiograph recording using a Holter monitor was performed during gastroscopy in 71 patients with stable CHD, to check for silent ischemia. To predict potential ischemia during gastroscopy, the Holter monitoring ECG was applied prior to a treadmill test, and withdrawn after gastroscopy 16-22 hours later. RESULTS: During gastroscopy, 30 patients (42%) had silent ischemia, but only 1 patient (1%) became symptomatic. Ischemia was dependent on heart-rate (median heart rate with ischemia 124 beats/min, without 104 beats/min). Abnormal findings on gastroscopy were found in 53 patients (75%). They implied a potential bleeding risk in 30 patients (42%) and prevented the indication for ASA in 6 of them (8%). CONCLUSIONS: Gastroscopy is potentially a harmful procedure for CHD patients, but the incidence of ischemic periods may be reduced by conscious sedation and, if the patient is receiving beta-blocking agent therapy, by applying this medication prior to gastroscopy.

Adult↗
PubMed2000

In vivo pedicle screw placement: image-guided virtual vision.

Near-real-time frameless stereotaxy registering intraoperative anatomy to a preoperative three-dimensional computer model has been developed for use with in vivo pedicle screw placement. Eight patients underwent thoracolumbar and lumbar spine stabilization surgery using this new technology, and 32 pedicle screws were placed. Three additional patients had 12 pedicle screws removed during revision surgery, and they allowed the authors to estimate the accuracy of this navigational system. Accuracy was determined by comparing pedicle screw position on postoperative computed tomographs for the first eight patients and on preoperative computed tomographs for the latter three patients, with the intraoperative computer trajectory data gathered during operation. In the group of eight patients, all screws were intrapedicular. In evaluating all 11 patients, the overall accuracy was +/- 2 mm, but the greatest error of 5.4 mm was noted in the sagittal plane measurement. During the development phase of this technology, time constraints prolong surgery, but this may be addressed once the tool's accuracy has been confirmed and intraoperative radiographic confirmation becomes unnecessary. In vivo real-time frameless stereotaxy for pedicle screw placement offers promise for the future. Refinements are needed to improve accuracy and address time constraints.

Bone Screws↗
PubMed1997

In vitro simulation. Early results of stereotaxy for pedicle screw placement.

STUDY DESIGN: Frameless stereotaxy with doppler ultrasound and three dimensional computer model registration is assessed in vitro for pedicle screw placement. OBJECTIVE: To identify feasibility of pedicle screw navigation and placement using this technology. SUMMARY OF BACKGROUND DATA: Inaccurate pedicle screw placement can lead to neurovascular injury or suboptimal fixation. Present techniques in pedicle screw placement involve only confirmation of hole orientation. METHOD: Forty-four pedicle screws were placed in lumbosacral models and cadaver specimens. Accuracy was assessed with a computed tomography scan and vertebral cross sectioning. RESULTS: All screws were intrapedicular. Accuracy of anterior cortical fixation was 1.5 mm, with a range of 2.5 mm. CONCLUSION: In vitro frameless stereotaxy is accurate for pedicle screw placement. This technology adds a component of navigation to pedicle screw placement.

Bone Screws↗
PubMed1991

In vivo non-invasive studies on the human lens.

Progress in biophysical technology now permits us to monitor aging and precataractous changes in the human ocular lens in vivo as well as in vitro. We are employing two noninvasive techniques to measure changes in lens fluorescence and in one lens water compartment (T2) utilizing Scheimpflug lens fluorescence densitography and magnetic resonance imaging. These studies demonstrate age-related changes in the normal lens as reflected by enhanced fluorescence and longer T2 values. Precataractous changes can also be detected with this approach.

Adult↗
PubMed1991

Phototoxicity involving the ocular lens: in vivo and in vitro studies.

Our laboratory has demonstrated the cataractogenic potential of UV radiation and several photosensitizing drugs in laboratory animals and in humans. We have utilized lens fluorescence measurements (which we have demonstrated to be a reliable marker for pre-cataractous and early cataractous changes), NMR pulse relaxation techniques, and our recently developed magnetic resonance imaging method to measure lens T2 values in the normal and UV exposed Degus lens (in vivo and in vitro) to detect pre-cataractous changes in the lens. These approaches will permit us to employ two parameters (increased non-tryptophan fluorescence and a decrease in T2 values) to monitor for such changes months before the lens opacities become manifest by conventional slit lamp examinations.

Animals↗
PubMed1987

Thyroid imaging with high-field-strength surface-coil MR.

Magnetic resonance (MR) imaging of the thyroid was performed with a 1.5-T system and local receiver coil in 19 "healthy" subjects and 34 patients with various focal and diffuse thyroid disorders. The normal gland was typically homogeneous with increased intensity relative to that of muscle on images obtained with long repetition times (TRs) and long echo times (TEs). Adjacent structures in the neck and upper mediastinum were well displayed. Thyroid nodules as small as 4-5 mm were identified. Follicular adenomas appeared as well-circumscribed nodules of heterogeneous intensity, increasing significantly in signal with long TRs/TEs. Colloid cysts and hemorrhagic cysts had homogeneous high signal with both short and long TRs/TEs. Two of three carcinomas were seen as poorly marginated lesions with associated cervical lymphadenopathy clearly depicted as increased intensity with long TRs/TEs. A follicular adenoma containing microscopic papillary carcinoma appeared similar to other benign adenomatoid nodules. A functioning nodule was isointense with normal gland at all pulse sequences. Characteristic patterns of diffuse abnormality were observed in cases of multinodular goiter, Hashimoto thyroiditis, and Graves disease, although additional cases are required to determine specificity. High-field-strength surface-coil MR imaging appears to be a sensitive method for identifying gross morphology of focal, multinodular, and diffuse disorders of the thyroid and involvement of surrounding structures in the neck.

Adult↗
PubMed1985

Temporomandibular joint: magnetic resonance imaging.

Magnetic resonance (MR) imaging of the temporomandibular joint was performed in two subjects using a 1.5 T experimental imaging system equipped with a 6.5 cm surface coil antenna. Normal and pathologic anatomy were demonstrated with exquisite detail. Anterior displacement of the joint meniscus was clearly visible in the symptomatic subject, consistent with arthrographic confirmation.

Adult↗
PubMed1981

Preparation and specificities of antisera to the amino-terminal sequence of the carcinoembryonic antigen.

A tetracosapeptide (peptide-24) corresponding to the amino-terminal sequence of the carcinoembryonic antigen (CEA) was synthesized and characterized. Antisera were produced to the peptide-24, and a radioimmunoassay was developed utilizing peptide-24 with a tyrosine residue on the amino-terminal end (Tyr-peptide-24). Inhibitions of anti-peptide-24-125I-Tyr-peptide-24 complex formation were done with several preparations of CEA and the normal cross-reacting antigen. The extent of cross-reactivities was low, one CEA preparation requiring a 250-fold molar quantity greater than peptide-24 to obtain the same degree of inhibition. Attempts to degrade the CEAs and normal cross-reacting antigens in order to possibly expose the amino-terminal ends for reactivity with antibody did not result in any great increase in inhibitory capacity. It was concluded that either the conformations of the antigenic determinant(s) of the peptide-24 and of the amino-terminal end of CEA were sufficiently different to result in little cross-reacting antigen are blocked for reactivity with antibody by other portions of the molecule.

Amino Acid Sequence↗
PubMed1979

[Zinc in the tissues: age dependence and local findings in cachexia, live cirrhosis and long-term intensive care].

Zinc concentrations in autopsy material of human heart muscle, skeletal muscle, iliac crest, pancreas and liver were analyzed by atomic absorption spectrophotometry. Age dependent differences of zinc concentrations are seen in the liver. High values shows liver of premature infants, a minimum is measured in childhood which is followed by an increase in adult and senile patients. The other organs show no significant changes. Different diseases like diabetes or liver cirrhosis do not influence the zinc concentration in skeletal muscles and iliac crest. Long-term intensive care patients show a marked decrease in zinc concentration of the heart muscle. In the cirrhotic liver the zinc pool is depleted. In diabetes mellitus zinc concentration of the whole pancreas is normal, in cachexia it is critically decreased.

Adult↗
PubMedDate not supplied

Endoscopic therapy for benign bile duct strictures.

Endoscopic therapy was attempted in 25 patients with benign strictures of the bile duct. In 23 patients, treatment involved endoscopic balloon dilation of the stricture zone or balloon dilation plus endoprosthesis placement. In 22 of 25 patients (88%), there was benefit from the endoscopic treatment. In 20 of 23 patients, there was significant radiographic improvement (p less than 0.001) in the diameter of their stricture following endoscopic therapy. All patients with elevated liver enzymes demonstrated rapid improvement following treatment. There was no significant morbidity or mortality associated with endoscopic treatment of benign biliary tract strictures. Follow-up study (mean, 4 +/- 0.3 years) discloses no recurrence of symptoms or elevated enzymes indicative of recurrent strictures. The treatment of benign bile duct strictures by a combination therapy of balloon dilation and stent placement provides a safe and effective treatment modality and an alternative to operative intervention.

Adolescent↗