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Biomedical subjects

B Davidson

Publications and source records attributed to B Davidson.

At least 37 records · Page 2Linked to original sources
PubMed1988

Leiomyomas of the duodenum.

Leiomyoma is a neoplasm of smooth muscle relatively common in the stomach, but very rare in the duodenal location. Symptoms are gastrointestinal bleeding or abdominal pain resembling peptic disease. Three cases of duodenal leiomyomas are described, and the importance of endoscopy is emphasized as a diagnostic tool. Surgical resection of the tumor is the recommended therapeutic procedure, and the difficulty in deciding at the pathological examination whether the leiomyoma is benign or malignant demands prompt follow-up of patients after surgery.

Aged↗
PubMed1988

Comparison of complications following frontal sinus fractures managed with exploration with or without obliteration over 10 years.

Two hundred twelve patients were treated for facial or skull trauma at the West Virginia University Hospital between the years 1977 and 1987. Sixty-six of these patients had frontal sinus or nasofrontal duct trauma. Follow-up information was obtained on 64 of these patients through clinic visits, chart review, questionnaires to patients and physicians, and telephone calls to the patients. Follow-up greater than 1 year was obtained on 52 patients. Sixty-four patients were managed either with a frontal sinus obliteration or with an open exploratory procedure. The incidence of complications occurring in the past 10 years after each of these procedures is compared. Because the indications for each procedure vary somewhat, data is presented on fracture etiology, associated injuries, specific fracture location, fracture displacement, severity of injury, and associated cerebrospinal fluid leaks.

Adolescent↗
PubMed1987

Porphyria--the UCT experience.

Several forms of porphyria are commonly seen in South Africa. Much of the knowledge accumulated in this field has been due to the meticulous research of Professor Lennox Eales and his colleagues at the University of Cape Town. Professor Eales headed the Porphyria Research Group, founded by the CSIR in 1957 and upgraded to a Unit by the MRC in 1979, until he retired in 1983. Since then porphyria research at UCT has continued within the MRC Liver Research Centre. We present here a description of those forms of porphyria commonly seen in South Africa, based in part on recent work carried out at UCT and in part on the work of Lennox Eales, to whom we dedicate this article.

Acute Disease↗
PubMed1979

Thiourea and cyanamide as inhibitors of thyroid peroxidase: the role of iodide.

Thiourea, methylmercaptoimidazole, propylthiouracil, and thiouracil are all potent inhibitors of thyroid peroxidase (TPO)-catalyzed iodination. Unlike the cyclic thioureylenes, thiourea at 5 mM has no effect on guaiacol oxidation. If iodide is added to guaiacol assays containing thiourea, enzyme activity is lost. The latter observation may be explained as follows. In the presence of iodide, the iodinating species [TPO.Ioxid], oxidizes thiourea to formamidine disulfide. This product decomposes to cyanamide at neutral pH. We have shown cyanamide to be an inhibitor of the peroxidative and iodinating functions of TPO. Studies in rats demonstrate that doses of thiourea which completely inhibit in vivo protein-bound iodine formation have no irreversible effect on TPO, as measured by guaiacol peroxidation after removal of the thyroids. The major in vivo action of cyanamide is similar to that of thiourea. The data suggest that the primary in vivo and in vitro mode of action of thiourea is the reversible Ioxid-trapping mechanism. The anomalous inhibition of guaiacol peroxidation seen in the presence of thiourea plus iodide derives from the formation of formamide disulfide, followed by its nonenzymic decomposition to cyanamide.

Animals↗
PubMed1978

The irreversible inactivation of thyroid peroxidase by methylmercaptoimidazole, thiouracil, and propylthiouracil in vitro and its relationship to in vivo findings.

A reinvestigation of the mechanism of action of methylmercaptoimidazole, propylthiouracil, and thiouracil on thyroid peroxidase (TPO) was undertaken. A preliminary incubation of TPO and H2O2 with methylmercaptoimidazole, propylthiouracil, or thiouracil was carried out in the absence of oxidizable substrates (i.e. I- or guaiacol). This incubation resulted in irreversible inactivation of TPO. The extent of inactivation could be determined after removal of the drug by gel filtration or by dilution into the assay mixture. Preincubation, as above, in the presence of iodide or thiocyanate prevented the irreversible inactivation of TPO. Rats receiving doses of these drugs which completely inhibited protein-bound iodine formation showed normal levels of TPO in their thyroid glands 30 min after drug administration. These findings suggest that the initial in vivo action of these drugs is to block iodination by trapping oxidized iodide, not by acting as "general inhibitors" of the TPO.

Animals↗
PubMed1977

Interaction of thyroid peroxidase with concanavalin A covalently coupled to agarose.

We have investigated the interaction between concanavalin A-agarose (Con A-agarose) and thyroid peroxidase, an integral membrane protein found in the 105,000 X g, 1-h particulate fraction of thyroid tissue. An intact form of porcine thyroid peroxidase was obtained by solubilization with the nonionic detergent Triton X-100 and two fragmented, hydrophilic forms of the enzyme were prepared by trypsin treatment of the membrane. The three types of thyroid peroxidase bind to Con A-agarose and can be eluted with alpha-methyl-D-mannoside. The alpha-methyl-D-mannoside eluate of the most purified thyroid peroxidase preparation has been analyzed by polyacrylamide gel electrophoresis. Peroxidase activity corresponds with a glycoprotein band. The binding of thyroid peroxidase to Con A-agarose can be inhibited by sugars in the following order: alpha-methyl-D-mannoside greater than D-mannose greater than alpha-methyl-D-glucoside greater than D-glucose greater than D-galactose. This order of specificity is typical of Con A-sugar interactions. Furthermore, inactivation of the carbohydrate binding site of Con A by demetallization greatly reduces the extent of thyroid peroxidase binding. Reactivation of the carbohydrate binding site by the addition of Ca2+ and Mn2+ to demetallized Con A-agarose restores thyroid peroxidase binding. These and other experiments suggest that htyroid peroxidase is, like several other peroxidases, a glycoprotein. In addition, the interaction between thyroid peroxidase and Con A-agarose may provide a new purification tool for thyroid peroxidase.

Animals↗
PubMed1976

Solubilization of thyroid peroxidase by nonionic detergents.

We have examined the ability of nonionic detergents to solubilize thyroid peroxidase from a porcine thyroid particulate fraction, as measured by the release of peroxidase activity into the supernatant fraction after centrifugation at 105,000 X g for 1 hour and the retardation of the supernatant peroxidase of Sepharose 6B. The parameters of peroxidase solubilization by Triton X-100 have been investigated in detail. Under optimum conditions, 60 to 95% of the thryoid peroxidase and about 50% of the total protein is released into the 105,000 X g, 1-hour supernatant. Under the optimum conditions established with Triton X-100, a series of Brij detergents of different chemical structure were equally effective in releasing peroxidase and protein. The protein patterns of the supernatants obtained with these detergents were similar on sodium dodecyl sulfate-polyacrylamide electrophoresis gels, suggesting that the detergents studied release similar membrane proteins. The Triton X-100 and Brij 58 supernatants were chromatographed separately on Sepharose 6B equilibrated with 0.1% Triton X-100 or Brij 58, respectively. In both cases, 75 to 80% of the peroxidase activity was retarded, thereby indicating that the nonionic detergents effect solubilization of the peroxidase rather than dispersal of nonsedimentable membrane fragments. These studies report the first successful solubilization of thyroid peroxidase by nonionic detergents. Together with previous evidence from our laboratory, these experiments indicate that thyroid peroxidase is an integral membrane protein.

Animals↗
PubMed1976

The development of the Generation II as an aid for patients with retinitis pigmentosa and night blindness.

The Generation II is a modification of the Army's night photography/observation instrumentaton. Low levels of light are intensified approximately 700 times to stimulate cone function. The individual with no rod function is able to see at night under these intensified amounts of illumination. The device can be used for night "spotting and mobility" purposes, much like a telescope is used during the day by the partially-sighted with intact rod function and poor cone function. This paper is presented to inform the optometrist of the availability and usefullness of this device for his patients.

Evaluation Studies as Topic↗
PubMed1975

Thyroid microsomal membrane proteins. Effects of solubilization on molecular size.

The molecular size of microsomal membrane proteins from frozen porcine thyroids before and after solubilization by proteolytic and non-proteolytic techniques has been investigated by means of polyacrylamide-gel electrophoresis in the presence of 1% sodium dodecylsulfate. When thyroid microsomal membrane proteins are solubilized by non-proteolytic methods such as high pH, n-butanol, or deoxycholate, no major change in the electrophoretic pattern compared to untreated microsomes has been observed, thereby suggesting that these non-proteolytic methods are capable of extracting membrane proteins from thyroid microsomes without altering their molecular size. However, treatment of microsomes with protein-solubilizing levels of trypsin (1-5 mug trypsin per mg thyroid protein) results in degradation of all major proteins with a molecular weight greater than 30 000. The high-molecular-weight proteins are particularly susceptible to attack by trypsin. Thus, these experiments indicate that the use of trypsin to solubilize thyroid microsomal membrane proteins, particularly thyroid peroxidase, will result in fragmented proteins and should be avoided if intact membrane proteins are desired.

Animals↗