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Biomedical subjects

D J Davis

Publications and source records attributed to D J Davis.

At least 19 recordsLinked to original sources
PubMed1992

Hill-Sachs lesion: comparison of detection with MR imaging, radiography, and arthroscopy.

Magnetic resonance (MR) imaging has proved to be a valuable method for documenting Hill-Sachs lesions. The authors retrospectively analyzed the diagnostic interpretations at plain film radiography, arthroscopy, and MR imaging in 76 patients. The analysis revealed that neither radiography nor arthroscopy displayed the lesion with sufficient accuracy to represent a true standard of reference for the evaluation of MR imaging in the diagnosis of the Hill-Sachs lesion. The data from the diagnostic interpretations were analyzed in three ways, each of which revealed that findings at MR imaging were more helpful than findings at radiography and/or arthroscopy in the diagnosis of the Hill-Sachs lesion. When the agreement of findings in two or three methods was used to assign a final diagnosis, MR imaging resulted in sensitivity of 97%, specificity of 91%, and accuracy of 94% in the detection of Hill-Sachs lesions.

Adolescent↗
PubMed1992

Insulin inhibits beta-adrenergic responses in fetal rabbit lung in explant culture.

Infants of diabetic mothers are at increased risk of a number of problems at birth. Among these problems are increased risks of respiratory distress syndrome and transient tachypnea of the newborn. Because surfactant synthesis, surfactant secretion, and lung fluid resorption are all mediated in part by beta-adrenergic responses, we asked if excess insulin interferes with the beta-adrenergic response cascade in fetal lung. Lungs from fetal rabbits (26 day) were grown in explant culture in hormone-supplemented culture medium. The explants were harvested after 48 h exposure to hormones and processed for determination of beta-adrenergic receptor concentration, guanine nucleotide regulatory proteins (Gs, Gi), beta-agonist stimulated adenosine 3',5'-cyclic monophosphate (cAMP) generation, cAMP-dependent phosphodiesterase activity, and choline incorporation into phosphatidylcholine. Although insulin did not change the concentration of beta-adrenergic receptors, it decreased the ability of isoproterenol to stimulate cAMP generation. Increase in stimulation over basal was similar in explants treated with dexamethasone and dexamethasone plus insulin, but absolute levels of isoproterenol-stimulated cAMP were less in the explants treated with dexamethasone plus insulin. We speculate that insulin inhibition of cAMP generation may be important in the pathogenesis of the respiratory problems of infants of diabetic mothers.

Animals↗
PubMed1992

Glomerular alterations in idiopathic haematuria--ultrastructural and morphometric analysis.

Re-evaluation of kidney biopsies has been done along with morphometric analysis of glomerular basement membrane thickness (G.B.M.) in 41 cases of idiopathic haematuria, in whom the initial routine light, immunofluorescent and electron microscopic examination had not shown any significant alterations. Extreme attenuation of G.B.M. (mean thickness of 2581 +/- 488 A) had been found in thirty one patients in contrast to mean GBM thickness of 4295 +/- 470 A found in control group. Absence of any history of familial haematuria in these patients distinguished them from hereditary nephropathies and hence categorized under the term thin basement membrane nephropathy. Follow up of these patients for upto 8 years had shown persistence of symptoms without further deterioration of renal function as well as morphology.

Adult↗
PubMed1990

Tryptophan fluorescence studies of ferredoxin:NADP reductase indicate the presence of tryptophan in or near the ferredoxin binding site.

The tryptophan fluorescence properties of the flavoprotein ferredoxin:NADP reductase have been examined. Although not sensitive to changes in pH or salt concentration, the tryptophan fluorescence is affected by the presence of substrates for the flavoprotein. While NADP addition results in a slight quenching of the fluorescence, ferredoxin decreases the fluorescence by nearly 50%, suggesting the presence of tryptophan in or near the ferredoxin binding site. Titration of this effect gives a dissociation constant for the ferredoxin: flavoprotein complex which is similar to that obtained by spectral perturbations. This approach has also been used to demonstrate that a chemically modified ferredoxin which does not produce spectral perturbations when added to flavoprotein is capable of interacting with the flavoprotein although with a higher dissociation constant than for native ferredoxin.

Binding Sites↗
PubMed1990

Beta-adrenergic receptors and cAMP response increase during explant culture of human fetal lung: partial inhibition by dexamethasone.

We studied beta-adrenergic receptors and responses in human fetal lung (15-25 wk gestation) maintained in explant culture with and without added dexamethasone. To determine beta-adrenergic receptor concentration, we performed radioligand binding assays with [125I]-iodocyanopindolol. We also examined the ability of isoproterenol to stimulate cAMP generation as a measure of response to beta-adrenergic receptor occupancy. In control cultures, beta-receptor concentration increased significantly from d 0 to 3 of culture and thereafter remained stable. The kd (approximately 24 pM) of [125I]-iodocyanopindolol did not change with time in culture. The ability of isoproterenol to stimulate cAMP generation over basal levels increased in controls throughout the 5 d in explant culture. Addition of dexamethasone (10 nM) to the culture medium partially blocked the increase in beta-receptor concentration and decreased both cAMP content and generation (basal and stimulated) in a dose-dependent manner (median effective concentration approximately 1 nM). In these same explants, dexamethasone increased the activity of fatty acid synthetase, an enzyme important in surfactant synthesis, more than 2-fold. Our results indicate that beta-adrenergic receptors and isoproterenol stimulation of cAMP generation increase spontaneously in human fetal lung grown in explant culture. Dexamethasone, which accelerates other aspects of human lung development in vitro, decreases beta-adrenergic receptor concentration and inhibits beta-adrenergic responses.

Cyclic AMP↗
PubMed1989

Plastocyanin cytochrome f interaction.

Spinach plastocyanin and turnip cytochrome f have been covalently linked by using a water-soluble carbodiimide to yield an adduct of the two proteins. The redox potential of cytochrome f in the adduct was shifted by -20 mV relative to that of free cytochrome f, while the redox potential of plastocyanin in the adduct was the same as that of free plastocyanin. Solvent perturbation studies showed the degree of heme exposure in the adduct to be less than in free cytochrome f, indicating that plastocyanin was linked in such a way as to bury the exposed heme edge. Small changes were also observed when the resonance Raman spectrum of the adduct was compared to that of free cytochrome f. The adduct was incapable of interacting with or donating electrons to photosystem I. Peptide mapping and sequencing studies revealed two sites of linkage between the two proteins. In one site of linkage, Asp-44 of plastocyanin is covalently linked to Lys-187 of cytochrome f. This represents the first identification of a group on cytochrome f that is involved in the interaction with plastocyanin. The other site of linkage involves Glu-59 and/or Glu-60 of plastocyanin to as yet unidentified amino groups on cytochrome f. Euglena cytochrome c-552 could also be covalently linked to turnip cytochrome f, although with a lower efficiency than spinach plastocyanin. In contrast, a variety of cyanobacterial cytochrome c-553's and a cyanobacterial plastocyanin could not be covalently linked to turnip cytochrome f.

Amino Acid Sequence↗
PubMed1988

Resonance Raman spectroscopy indicates a lysine as the sixth iron ligand in cytochrome f.

The resonance Raman spectrum of turnip cytochrome f is similar to that of other c-type cytochromes with the exception of a single band at 1532 cm-1 which is shifted to lower frequency relative to its position (1542-1545 cm-1) in other c-type cytochromes. Comparison of the frequency of this band with that in alkylated cytochrome c at high pH suggests that the sixth heme iron ligand in cytochrome f is a deprotonated lysine amino group rather than a methionine sulfur. Comparison of the amino-acid sequences of cytochromes f and c1 suggests lysine-145 as a likely candidate for the sixth heme iron ligand in cytochrome f.

Amino Acid Sequence↗
PubMed1987

Beta-adrenergic receptors and cyclic adenosine monophosphate generation in human fetal lung.

We designed experiments to determine whether beta-adrenergic receptors are present and functional in human fetal lung during the 2nd trimester of gestation. To determine the presence of beta receptors, characterize their binding sites, and assess changes in receptor with gestational age, we performed radioligand binding assays with the specific, high-affinity beta antagonist, 125I-iodocyanopindolol, in membrane particulates from the lungs of 2nd trimester abortuses (15-23 wk). Binding of 125I-iodocyanopindolol was saturable and of high affinity (dissociation constant = 40 pM). Binding was stereoselective as determined by competition studies with (-) and (+) stereoisomers of propranolol. Agonist affinities (isoproterenol greater than epinephrine much greater than norepinephrine) were consistent with a predominance of beta-2 receptors; this predominance was confirmed by competition studies with the specific beta-2 receptor antagonist ICI 118-551 (75% beta-2, 25% beta-1). The concentration of beta-adrenergic receptors increased with gestational age. To assess the functional coupling of the beta receptors, we tested the ability of receptor occupancy to activate adenylate cyclase. For this assay, we incubated minced human fetal lung with beta agonists and determined the amount of cAMP generated. beta Agonists stimulated cAMP generation more than 2-fold. We conclude that beta-adrenergic receptors are present and functional in human fetal lung as early as the 2nd trimester.

Alprostadil↗
PubMed1977

Birth order and intellectual development: the confluence model in the light of cross-cultural evidence.

For Israeli eighth-grade students of Asian-African origin, achievement decreases as a function of birth order in small families and increases as a function of birth order in large families. This finding cannot be accounted for by differences in developmental rate or size of birth intervals. It can be accounted for by considering the effect of external influences, such as schooling, on intellectual development.

Achievement↗
PubMed1976

Protein-protein interactions of the light-harvesting chlorophyll a/b protein. II. Evidence for two stages of cation independent association.

In a previous paper, we observed a two-stage cation-independent association of the light-harvesting chlorophyll a/b protein from spinach chloroplasts based on concentration-dependent changes in the sedimentation coefficient. The two stages of association occurred between (2-4) and (4-7) mug/ml chlorophyll. In this paper, we provide further evidence for this association. This includes: (1) A decrease in the number of divalent cation binding sites in the second stage of association. (2) A corresponding decrease in the extent of the cation-dependent association. (3) A positive deviation from Beer's law for chlorophyll b for both stages of the cation-independent association and a positive deviation for chlorophyll a for the second stage of association only. (4) A change in the fluorescence emission of both chlorophyll a and b. The change for chlorophyll b was observed for both steps of association whereas that for chlorophyll a was observed for the second step of association only. Therefore, the first stage of association affects only chlorophyll b whereas the second stage alters the environment of both chlorophyll a and b. (5) In addition, divalent cations quenched chlorophyll fluorescence. However, the quenching which required 200-300 muM divalent cation for half-maximal effects was related neither to divalent cation binding nor to the divalent cation-induced association of the protein.

Aerobiosis↗