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Biomedical subjects

A Bigi

Publications and source records attributed to A Bigi.

67 records · Page 4Linked to original sources
PubMed1977

X-ray diffraction and scanning electron microscopy of bovine media aortic wall.

Scanning electron microscopy and high angle X-ray diffraction were used to define the relationship between collagen and elastin of bovine aortic wall. The diffraction pattern shows on one hand that the broad rings at 4.5 A and 9 A, due to elastin, do not orient on stretching and on the other hand, that the collagen rings at 11 A and 2.9 A start to orient at low elongations. These data together with scanning electron microscopy suggest a tight structural relationship between collagen and elastin that should influence the mechanics of deformation at all degrees of elongation.

Animals↗
PubMedDate not supplied

Hydroxyapatite-gelatin films: a structural and mechanical characterization.

Composite films of gelatin and hydroxyapatite were prepared and characterized by mechanical tests, scanning electron microscopy and X-ray diffraction investigation. The mechanical properties of the films are greatly affected by the presence of hydroxyapatite and change as a function of inorganic phase content. On stretching, the long axis of the collagen molecular portions align parallel to the direction of deformation and the gelatin coarse layered structure becomes more evident and ordered. Furthermore, under deformation the inorganic crystals, which are embedded in the gelatin layers, seem to squeeze out in the interlayer spaces and assume a preferential orientation parallel to the force trajectories. Thus, as the inorganic phase stiffens the gelatin films, the macromolecular matrix distributes the stress promoting the preferential orientation of the apatitic crystals. The results indicate that this experimental approach can be used to prepare composites with anisotropic properties, which can be modulated through variation in composition and mechanical deformation in order to get biomaterials suitable to fulfill specific mechanical functions.

Animals↗
PubMedDate not supplied

Are double-blind food challenges necessary before starting an elimination diet?

Food allergy is normally treated by eliminating the offending food. Such a measure, however, may cause nutritional and sociopsychological problems, so an allergy must be diagnosed with the utmost certainty. To date the most reliable diagnostic test is the double-blind food challenge (DBFC). The rationale for using this test is the marked difference in positive results with open and double-blind food challenges. Only about 30% of open challenges that appear positive are confirmed on blind challenge. There is ample evidence, too, that a negative DBFC may in fact indicate tolerance to that food. From the literature it appears that almost all patients who reintroduced a certain food into their diet after a DBFC had given negative findings did not present any adverse reaction to it. In our caselist of 21 patients with probable reactions to foods but negative DBFC, 19 (90.5%) tolerated the "incriminated" food well when it was reintroduced into their diet even in unlimited amounts. Only two (9.5%) again presented symptoms when they started taking large amounts of the problem food. Therefore, one precaution recommended before reintroducing a food item into a patient's diet after a negative DBFC is to check how it is tolerated at high doses. A review of the literature confirms the unquestioned utility of the DBFC. Nevertheless, in some situations this test is not indicated. The main one, of course, is in patients with life-threatening symptoms such as anaphylactic shock or glottis edema, in whom any provocation test is contraindicated.(ABSTRACT TRUNCATED AT 250 WORDS)

Diet↗
PubMedDate not supplied

A conformational model for the action of general anesthetics at the membrane level. I. Theoretical considerations.

The first paper of this series describes a working hypothesis for the action of general anesthetics. According to such hypothesis, anesthetics, by inducing a labilisation of lipid-protein interactions in biomembranes, affect the conformation, and hence the activity of membrane-bound catalytic proteins. It is conceivable that such changes in ionic channels in neuronal membranes will abolish the transmission of nervous impulses and give rise to anesthesia. The hypothesis is discussed on the basis of previously known experimental data and of theoretical considerations. Thermodynamic considerations are in favour of the idea that a rupture of lipid-protein interactions will expose protein groups to water destabilising helical structures. A large decrease of alpha-helical content after lipid removal had been previously found. Furthermore lipids affect the kinetics of membrane-bound enzymes, suggesting that conformational changes occur in the catalytic site after lipid removal or perturbation.

Anesthesia, General↗
PubMedDate not supplied

A conformational model for the action of general anesthetics at the membrane level. II. Experimental observations on the effects of anesthetics on lipid fluidity and lipid protein interactions.

We have investigated the effect of general anesthetics (the normal alcohol series up to pentanol, halothane, pentrane, ether, chloroform, and ketamine) on lipid fluidity of phospholipid vesicles and mitochondrial and erythrocyte membranes by using spin labels and fluorescent probes. The spin labels used (5- and 16-doxyl stearic acids) show that all anesthetics tested have a slight fluidizing effect on lipid vesicles but induce a very strong increase in mobility of spin labels in mitochondria and lower in erythrocyte ghosts. These results are interpreted as a labilization of lipid protein interactions at all depths in the bilayer. The fluorescent molecules ANS and NPN, which probe the glycerol region and the core of the bilayer respectively, show a decrease of fluorescence induced by alcohols, halothane, ether, chloroform in both lipid vesicles and membranes. The decrease of fluorescence is due to decreased quantum yield as shown by double reciprocal plots of probe fluorescence against membrane concentration. The fluorescence decrease is interpreted mainly as an increase in fluidity of the lipid bilayer and not as an increase of polarity of the probe environment. The effect of ketamine is that of fluidization in the bilayer core (NPN) but of increased rigidity in the glycerol region (ANS) perhaps due to the amphipathic character of this anesthetic, that is supposed to bind in the polar region of the bilayer. Pentrane also induces fluidization in the bilayer core (NPN) but has a peculiar effect near the surface (ANS): in lipid vesicles it induces a fluorescence decrease, whereas an increase is seen in mitochondrial membranes. These complex effects are considered as the result of some specific change in the lipid protein interactions in the region probed by ANS. The effects of anesthetics on maximal NPN fluorescence (Fo) have been usually found to be stronger in mitochondrial membranes than in lipid vesicles, thus confirming the results of the spin label studies, showing a labilization of lipid protein interactions induced by anesthetics. The effects on Fo of ANS, however, appear to be stronger in lipid vesicles than in membranes. These findings indicate that the presence of the proteins counteracts the perturbation induced by anesthetics at the level of the membrane surface, in contrast with the disruption of lipid protein interactions observed in the membrane hydrophobic areas.

Anesthesia, General↗