Search PubMed⌕ Search

Biomedical subjects

M G Woldring

Publications and source records attributed to M G Woldring.

At least 37 records · Page 2Linked to original sources
PubMed1982

An electromagnetic valve for rebreathing exercise studies.

An electromagnetic valve for use in exercise rebreathing studies is described. This valve enables the investigator to connect a rebreathing system immediately after the onset of inspiration even at high breathing frequencies. The rapid switching causes minimal leakage; the rebreathing bag can be washed out and refilled without disconnection during exercise testing. For one year this valve has been used in measurements of functional residual capacity and diffusing capacity during exercise in volunteers as well as in patients.

Electromagnetic Phenomena↗
PubMed1982

Radiotracers binding to estrogen receptors: I: Tissue distribution of 17 alpha-ethynylestradiol and moxestrol in normal and tumor-bearing rats.

Ethynylestradiol and moxestrol can be labeled with carbon-11 by introducing this positron emitter in the 17 alpha-ethynyl group. To investigate their potential as radiotracers binding to estrogen receptors, we studied the tissue distribution of tritiated ethynylestradiol and moxestrol, with specific activities of 57 Ci/mmol and 77-90 Ci/mmol, respectively, in the adult female rat. At 30 min after injection, both compounds showed specific uptake in the uterus (% dose/g): 2.52 for ethynylestradiol and of 2.43 for moxestrol. A decrease of the specific activity to 6-9 Ci/mmol resulted in uterine uptakes of 1.60 and 2.10 respectively, for ethynylestradiol and moxestrol, at 30 min. In the female rat bearing DMBA-induced mammary tumors, specific uptake was also measured in the tumors, although the values were only 25-30% of the uterine uptake. Moxestrol showed a greater uptake selectivity in the tumors compared with ethynylestradiol. From this study we conclude that ethynylestradiol and moxestrol have good potential as tracers binding to mammary tumors that contain estrogen receptors.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1981

Extraction of water labeled with oxygen 15 during single-capillary transit. Influence of blood pressure, osmolarity, and blood-brain barrier damage.

By external detection, the influence of arterial blood pressure (BP), osmolarity, and cold-induced blood-brain barrier damage was assessed on the extraction of water labeled with oxygen 15 during single-capillary transit in the rat. There was an inverse relation between arterial BP and extraction that was attributable to the influence of arterial BP on cerebral blood flow (CBF) and the relation between CBF and extraction. Neither arterial BP nor osmolarity of the injected bolus had any direct effect on extraction of water 15O, signifying that the diffusional exchange component (determined by blood flow) of extraction greatly surpasses the convection flow contribution by hydrostatic or osmotic forces. Damage to the blood-brain barrier did not change its permeability to water.

Animals↗
PubMed1980

An improved method for the analysis of xenon-133 washin and washout curves.

A method is described for analysis of xenon-133 washin and washout curves, in the presence of a slowly varying background. The method uses least-squares fitting of a single exponential together with a quadratic function to correct for the background. The method has been applied both to simulated data and to data from 25 patients. The accuracy in the relevant lung parameters was 5% over a wide range of the specific ventilation. A comparison is made with other methods in use to measure regional lung-function parameters. Our method produces reliable results even when specific ventilation is low, which can occur in patients with chronic airflow obstruction, where other methods may incur errors of more than 45%.

Airway Obstruction↗
PubMed1979

Specificity of immunoassays. II. Heterogeneity of specificity of antibodies in antisera used for steroid immunoassay and the selective blocking of less specific antibodies, including a new method for the measurement of immunoassay specificity.

Practical aspects of the measurement of the specificity of immunoassay are reviewed. Antibody heterogeneity in an antiserum makes a pragmatic rather than a theoretical approach necessary. A new method for the measurement of immunoassay specificity is described. This method is based on the errors caused by the cross-reacting antigens and is directly relevant to the validity of results obtained by immunoassay methods. The effect of selectively blocking the least specific antibodies in antisera raised against steroid haptens is tested. The practical consequences of these considerations are tested using steroid radioimmunoassay and enzyme-immunoassay.

Androgens↗
PubMed1979

Specificity of immunoassays. III. Use of two antisera of differing specificities to improve the specificity of steroid immunoassay.

The specificity of immunoassays can be improved by using a second antiserum to bind substances that cross-react. Both theory and practice show that the effectiveness of the procedure is dependent of the complex interplay of the concentrations of the two antibodies, the concentrations of the three antigens involved (the labelled tracer, the antigen whose concentration is to be measured and the substance that cross reacts) and the affinities of the antibodies for these antigens. Measured cross-reactions can frequently be reduced to zero in the most important concentration ranges thereby enabling one to perform assays upon unpurified materials which other wise would not be possible. Limitations of the method are discussed.

Androstenedione↗
PubMed1978

Rapid decarboxylation of carbon-11 labelled DL-DOPA in the brain: a potential approach for external detection of nervous structures.

The cerebral distribution of the positron-emitting agent [1-11C]beta-(3,4-dihydroxyphenyl)-D,L-alpha-alanine ([11C]DOPA) was studied after intravenous injection in rats pretreated with the peripheral decarboxylase inhibitor, carbidopa. Within 15 min of injection the accumulation of carbon-11 was almost twice as high in cortical areas and cerebellum as in the striatum and the brain stem. After destruction of catecholamine-containing nerve endings with 6-hydroxydopamine, the level of carbon-11 in the striatum was higher than in rats not treated with this neurotoxin. Pretreatment of rats with haloperidol or L-DOPA did not change the distribution pattern of carbon-11. Without pretreatment with carbidopa a uniform distribution of the label in the brain was observed. We suggest that [11C]DOPA is a potentially useful agent for external detection with positron imaging systems in patients and large animals of brain regions rich in the enzyme dopa-decarboxylase. (EC 4.1.1.26).

Animals↗
PubMed1978

Chemiluminescence-linked immunoassay.

Covalent complexes of a chemiluminescent compound (a luminol derivative), protein and a steroidal hapten have been used as a labelled antigen in a way analogous to the radioactive label in radioimmunoassay. The antibody-bound complex emits light when treated with hydrogen peroxide and copper acetate at high pH. The chemiluminescent complex bound to antibody can be displaced by free steroid to produce a standard curve in a way analogous to radioimmunoassay.

Animals↗
PubMed1978

Analysis of extramedullary erythropoiesis in the spleen by a semiquantitative method using indium-111.

A semiquantitative method for evaluating the splenic uptake of 111In is described. With this method the uptake of indium in the spleen was significantly higher in seven patients with extramedullary erythropoiesis (EME) than in a control group of seven patients with comparable degrees of splenomegaly but without clinical and/or histological signs of EME. The discrimination between these groups could be further improved by also taking the degree of splenomegaly into account. It is concluded that the described technique is a valuable non-invasive aid for establishing the presence of EME in the spleen.

Adult↗
PubMed1978

Clinical evaluation of radio-labelled bleomycin for tumor detection.

Investigations with bleomycin labelled with radionuclides other than 57Co in patients with cancer and in tumor-bearing animals are described. In patients 57Co-bleo appears to be a better tumor-seeking radiopharmaceutical than 111In-bleo, 99mTc-bleo or 197Hg-bleo. This can be explained by a higher stability in vivo and a better tumor-seeking property of 57Co-bleo and less disturbing activity in the cardiac pool and in bone and other normal tissues when assessing the scintigram. Results with 111In-bleo labelled in acidic solution are not essentially different from those with 111In-bleo labelled in neutral solution. Results of 197Hg-bleo are almost identical with those of 197HgCl2 regarding the tumor-seeking effect as well as the distribution in normal tissues and organs. Probably the complex of 197Hg to bleomycin is not stable in vivo. The superiority of 57Co-bleo over 99mTc-bleo, 197Hg-bleo and also over 67Cu-bleo is confirmed by experiments on tumor bearing animals. We may conclude that the indication for use of bleomycin as a tumor-seeking pharmaceutical labelled with 111In, 99mTc, 197Hg or 67Cu seems to be very limited.

Animals↗