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Biomedical subjects

L Leonardi

Publications and source records attributed to L Leonardi.

At least 55 records · Page 3Linked to original sources
PubMed1987

Cardiovascular effects of verapamil in essential hypertension.

Calcium antagonists may affect the regulation of body sodium and adrenergic-dependent mechanisms. Exchangeable sodium, blood volume, plasma norepinephrine, renin, aldosterone, pressor responsiveness to norepinephrine, heart rate responses to isoproterenol, and lipid metabolism were studied in 15 patients with essential hypertension after 8 weeks of treatment with verapamil (348 +/- 68 (SD) mg/day). Supine blood pressure decreased from 153/103 +/- 19/12 mm Hg to 140/95 +/- 14/12 mm Hg (P less than 0.01). Exchangeable sodium, blood volume, plasma norepinephrine, renin and aldosterone, serum total cholesterol, the lipoprotein fractions, and apoprotein levels were unchanged. The norepinephrine pressor and the isoproterenol chronotropic doses tended to increase, whereas the dose-response curve of blood pressure related to plasma norepinephrine was significantly displaced to the right (F = 5.34; P less than 0.05). The antihypertensive effect of verapamil is associated with a decreased cardiovascular pressor responsiveness to norepinephrine without changes in endogenous noradrenergic activity. Moreover, verapamil does not modify the sodium/fluid volume state, the activity of the renin-angiotensin aldosterone axis, or lipid metabolism.

Adult↗
PubMed1986

"In vitro" fibril formation of type I collagen from different sources: biochemical and morphological aspects.

Acid soluble type I collagen was prepared from foetal and adult bovine tendon and skin and from adult bovine cornea. The degree of hydroxylysine glycosylation and the hydroxylysine di-to monoglycoside ratio as well as the "in vivo" fibril diameters, were shown to be tissue and age-dependent. Fibrils of type I collagens were reconstituted "in vitro" monitoring at 313 nm. The fibrils obtained were examined by electron microscopy. It was shown that the "in vitro" lateral growth of collagen fibrils leads to the formation of fibrils with maximum diameters which may be correlated to those of the corresponding native fibrils. Moreover it is suggested that one of the factors controlling the lateral growth of collagen may be at the level of hydroxylysine glycosylation.

Animals↗
PubMed1985

Ultrastructural aspects of rat tail tendon sheaths.

An investigation was carried out on the sheaths which envelop rat tail tendons. The samples were processed for observation by light and electron microscopy. In the case of electron microscopy, thin sections of specimens embedded in epoxy resin and replicas of freeze etched samples were used. On the basis of histological and ultrastructural observations, four distinct connective tissue sheaths have been detected. The paratendineum is a thick fibrous sheath that covers externally the four groups of tendons arranged around the vertebrae of the tail; the epitendineum is a distinct fibrous sheath surrounding each tendon group; the peritendineum is composed of concentric cellular laminae enveloping each tendon; lastly, the endotendineum is made up of one cellular lamella which adheres to the fibres of the tendon, projecting trabeculae between the individual tendon fascicles. In the para- and epitendineum, thick bundles of collagen fibrils, running parallel to the fibres of the tendon, were visible. The collagen fibrils had a wide variability of diameters (from 35 to 220 nm) and, when examined in replica, their microfibrillar arrangement appeared to be straight. In the peri- and endotendineum, thin bundles of collagen fibrils were visible between the cellular laminae, parallel to the main axis of the tendon. Among these collagen bundles, elastic fibres and numerous glycoproteins containing microfibril-like filaments were visible. The collagen fibrils were small and of uniform diameter (50 nm) and, when observed on replica, showed a helicoidal microfibrillar arrangement. The cell layers of the peri- and endotendineum were made up of flattened fibroblasts which were connected by specialised junctions and which contained numerous micropinocytotic vesicles. A thin layer of granular electron-dense material, with ultrastructural characteristics similar to those of a basement membrane, was visible on the surface of the most external cellular layer of the peritendineum and on the outer surface of the cellular lamella of the endotendineum. Due to their morphological characteristics it is supposed that the four tendon sheaths are involved in different and special functions. Moreover, collagen Type I and collagen Type III, demonstrated by means of immunofluorescence techniques in previous investigations, show respectively a close similarity in distribution to the thick collagen fibrils, with a straight microfibrillar arrangement, of the two external sheaths, and to the thin collagen fibrils, with a helicoidal microfibrillar arrangement, of the two internal sheaths.

Animals↗
PubMed1984

Phospholipid-enriched bacterial chromatophores. A system suited to investigate the ubiquinone-mediated interactions of protein complexes in photosynthetic oxidoreduction processes.

Fusion of phospholipid vesicles with photosynthetic chromatophores from Rhodopseudomonas sphaeroides was induced by freezing and thawing. After sucrose density gradient sedimentation, bands containing closed vesicles characterized by different phospholipid to reaction center molar ratios could be isolated and analyzed morphologically and functionally by means of electron microscopy and fast spectroscopy, respectively. Analogously to data reported for phospholipid-enriched mitochondrial inner membranes (Schneider, H., Lemasters, J. J., and Hackenbrock, C. R. (1982) J. Biol. Chem. 257, 10793), the rate of photosynthetic electron transfer in phospholipid-enriched chromatophores decreased with increasing distance between integral membrane complexes. A fast cyclic electron transfer could be restored when the concentration of the ubiquinone pool within the lipid bilayer was reconstituted by additions of exogenous ubiquinone. These results suggest that cyclic electron transfer between reaction center and ubiquinol-cytochrome c2 oxidoreductase complexes in phospholipid-enriched chromatophores is limited by the lateral diffusion of the quinone molecules in the membrane plane. The observation that dilution of the quinone pool in the lipid bilayer affects the rate of photosynthetic electron transport contrasts with previously reported data which indicated that up to 80% of the quinone pool can be removed without altering the kinetic parameters of the overall process. These conflicting results can be reconciled by a model which assumes that the relative orientation of the protein complexes, possibly controlled by protein-protein interactions within the lipid bilayer, plays a key role in the effectiveness of the molecular collisions. According to a diffusion-limited mechanism, this would lead to a fast electron transfer during the photosynthetic reactions.

Bacterial Chromatophores↗
PubMed1983

[Relation between the distribution and orientation of collagen fibers and the inorganic phase of calcification processes in the anterior leaflet of the human mitral valve].

The collagen fibers observed in calcified valves appear randomly distributed without any preferential arrangement. In these areas also the hydroxylapatite crystals do not show any orientation. It is suggested that the disorder of the organic phase is a factor favouring the deposition of the calcium crystals.

Calcification, Physiologic↗
PubMed1983

Light microscopy, electron microscopy, and X-ray diffraction analysis of glycerinated collagen fibers.

Light microscopy, transmission electron microscopy (freeze-fracture replicas and thin sections), and X-ray diffraction techniques were used to investigate the structure of rat tail tendon collagen fibers subjected to one of the following treatments: water, phosphate buffer, glutaraldehyde, glutaraldehyde followed by glycerol, glycerol, and glycerol followed by phosphate buffer. As seen by light microscopy, only treatment with glycerol induces a remarkable swelling of the native (untreated) collagen specimens. Replicas and thin sections show that this swelling is due to an expansion of the interfibrillar space, and to a dissociation of the collagen fibrils into microfibrils. X-Ray diffraction analysis reveals great disorder in the glycerol-swollen collagen fibers. However, this does not appreciably involve the microfibrillar and molecular structure. Light and electron microscopy as well as X-ray diffraction techniques show that the collagen fiber swelling induced by glycerol is an almost completely reversible process.

Animals↗
PubMed1983

The banding pattern of rat tail tendon freeze-etched collagen fibrils.

Banding patterns of freeze-etched and replicated rat tail tendon collagen fibrils were studied. Better banding definition was obtained by freezing the samples without using a cryoprotectant and by prolonging etching. Under these conditions, the banding pattern was characterized by a sequence of elevated and depressed segments with a D-period of 65 nm, by two ridges at the margins of the elevations and by a third ridge at an intermediate point in the depressions. A comparison between replicas and isolated negatively stained collagen fibril micrographs as well as densitometric determinations have allowed interpretation of the elevations and depressions as overlap and gap zones and of the three ridges as the main bands with higher molecular density. Estimates, carried out on densitometric diagrams obtained from replicas, gave values which may represent a new parameter in the study of collagen banding and led to the calculation of a 0.55 D long gap zone and of a 0.45 D long overlap zone.

Animals↗
PubMed1982

[Ultrastructural findings on collagen fibers of tendon sheaths from the rat tail].

Rat tail tendon sheaths have been studied by electron microscopy and freeze-etching techniques. Pictures from thin sections have shown the presence of three different sheaths: a) a sheath commun to all tendons, (paratenon) formed by collagen fibrils differently orientated with a variable diameter (20nm 200nm) b) a specific sheath for every tendon, (peritenoneum) which is composed by different layers: the external ones present collagen fibrils of wide and variable diameter (20nm-200nm). The internal ones present collagen fibrils of uniform and small diameter (50nm-60nm). Between these fibres layers, there is evidence for the presence of fibrocits forming continuous cellular layers. c) a sheath surrounding tendon fascicles, (endotenoneum) formed by small and uniform collagen fibrils and a continuous cellular layers. Replicas of freeze-fractured collagen fibrils having a variable diameter show a straight arrangement of their microfibrils.

Animals↗
PubMed1982

[Electron microscope observations on the microfibrillar arrangement of collagen fibers in the tail tendon of the rat].

We have examined the rat tail tendon microfibrillar arrangement by electron microscopy and freeze-etching technique. Collagen fibers have been examined in unstretched and stretched conditions. Our data indicate the freeze-etching technique as a particularly useful to interpretate the microfibrillar arrangement. We are able to observe that the microfibrils are arranged in straight lines along the axis of the fibrils. The most suitable condition for the interpretation of this datum is obtainable when: 1) the fibers are stretched and therefore the crimping are reduced; 2) the fracture movement follows a direction parallel to the bulk fiber axis.

Animals↗
PubMed1982

[Ultrastructural studies of tissue surrounding endosseous dental implants].

We have observed peri-implant tissue specimens of endosseus dental implants subjected or not to occlusal load. All the specimens showed a large network of collagen microfibrils and proteoglycans filaments, strictly adherent to the endoprothesis. In some cases a layer of connective tissue surrounds the proteoglycan network only in some peri-implant areas. Cellular and extracellular components of this connective tissue were orientated parallel to the metal surface and all this appears to be correlated to a definite biological function.

Collagen↗
PubMed1980

[Distribution of proteoglycans in the sclera].

The Authors have studied, with histochemical methods, the manner of proteoglycans distribution in superficial and deep layers of the sclera, which are characterized by structural differences regarding collagen. The pictures, on one hand, are in agreement with biochemical data which indicate the presence of dermatan-sulfate, chondroitin-sulfate and hyaluronic acid, on the other hand, show a marked glycosaminoglycans distribution in the deep layers and a lessening of their distribution relative to the superficiality of the layers. Furthermore alcianophilic particles are visualized at the electron microscope. In the superficial layers such particles are in direct relation, often periodically, with the collagen fibrils, while in the deep layers particles without this direct relationship are also observable. The Authors point out a topographic coincidence between variations regarding the proteoglycans distribution and variations regarding collagen. Moreover, the obtained pictures suggest the existence of a particular proteoglycans-collagen interaction corresponding to the deep layers where fibrillogenesis occurs.

Animals↗
PubMed1980

[Ultrastructure of collagen fibers in the sclera].

The Authors have studied the microfibrillar packing of the scleral collagen fibrils on thin sections of samples treated with a dissociant agent and on replicas of freeze-fractured fibrils. The only difference in observing the fibrils between the external and internal layers is relative to the diameter, evidencing in general, lower dimensions in the latter. The microfibrillar packing is characterized by a lightly spiralized or wavy running of filamentous subunits and the same is evident in fibrils of different diameter. The ultrastructural pictures are similar to those obtained in the other tissues, such as tendons, fibrous cartilages, fibrous capsules of parenchymatous organs and ligaments, in which the collagen is predominantly type I, like in the sclera.

Animals↗
PubMed1980

[X-ray diffraction analysis of collagen fibers processed with glutaraldehyde and glycerol].

Rat tail tendon collagen fixed with glutaraldehyde and treated with glycerol has been studied by X-ray diffraction technique. The evaluation of the distribution of the areas at higher and less density of molecular packing in the collagen fibrils has been carried out through the analysis of the intensity distribution of the low angle X-ray diffraction maxima. The results show that this treatment usually employed in the freeze-etching technique induces a modification of the degree of order in specific regions inside the axial period D.

Aldehydes↗
PubMed1980

[Role of the orientation of the collagen fibers on the mechanical properties of the carotid wall].

Mechanical test was applied to several carotid walls air-dried under different degree of deformation along the circumferential direction. The stress-strain curves show an increase of the elastic modulus as a function of the deformation. X-ray diffraction studies were applied to determine the degree of collagen orientation in the deformed samples. The carotid wall, in agreement with the "composite materials theory", shows that the collagen is the most responsible factor of the mechanical properties of the tissue.

Animals↗
PubMed1975

Influence of sulpiride on gastrointestinal motility: experimental radiological study in the dog.

A radiological study has been carried out in the dog to control the influence of N-ethyl-2(2-methoxy-5-sulfamido-benzamidomethyl)-pyrrolidine (sulpiride) on the motility of the gastrointestinal tract. The drug was administered orally and parenterally at different doses for each pharmaceutical form and for such route of doses for each pharmaceutical form and for each route of administration. In doses which were considered optimal, the results have demonstrated that sulpiride exerts hypertonic and hyperphasic effects on the smooth musculature of the gastrointestinal tract. Consequently, there is a reduction of the transit time and of the emptying of the opaque meal in the various sectors of the gastrointestinal tract, which is in the order of about 50% with respect to normal. Using doses which are inferior to those considered optimal, no significant results were obtained, while following higher doses the action of sulpiride is manifested by an inhibitory effect on gastrointestinal motility.

Administration, Oral↗